draft-ietf-tcpm-converters-00.txt   draft-ietf-tcpm-converters-01.txt 
TCPM Working Group O. Bonaventure TCPM Working Group O. Bonaventure, Ed.
Internet-Draft Tessares Internet-Draft Tessares
Intended status: Experimental M. Boucadair Intended status: Experimental M. Boucadair, Ed.
Expires: August 20, 2018 Orange Expires: September 6, 2018 Orange
B. Peirens B. Peirens
Proximus Proximus
S. Seo S. Seo
Korea Telecom Korea Telecom
A. Nandugudi A. Nandugudi
Tessares Memphis University
February 16, 2018 March 05, 2018
0-RTT TCP Converter 0-RTT TCP Convert Protocol
draft-ietf-tcpm-converters-00 draft-ietf-tcpm-converters-01
Abstract Abstract
This document specifies an application proxy, called Transport This document specifies an application proxy, called Transport
Converter, to assist the deployment of Multipath TCP. This proxy is Converter, to assist the deployment of TCP extensions such as
designed to avoid inducing extra delay when involved in a network- Multipath TCP. This proxy is designed to avoid inducing extra delay
assisted connection (that is, 0-RTT). This specification assumes an when involved in a network-assisted connection (that is, 0-RTT).
explicit model, where the proxy is explicitly configured on hosts. This specification assumes an explicit model, where the proxy is
explicitly configured on hosts.
Status of this Memo -- Editorial Note (To be removed by RFC Editor)
Please update these statements with the RFC number to be assigned to
this document:
[This-RFC]
Please update TBA statements with the port number to be assigned to
the Converter Protocol.
Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 6, 2018.
This Internet-Draft will expire on August 20, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Applicability Scope . . . . . . . . . . . . . . . . . . . . . 5 2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Sample Examples of Converter-Assisted Multipath TCP 3.1. Functional Elements . . . . . . . . . . . . . . . . . . . 5
Connections . . . . . . . . . . . . . . . . . . . . . . . 9 3.2. Theory of Operation . . . . . . . . . . . . . . . . . . . 7
3.2. Sample Example of Incoming Converter-Assisted 3.3. Sample Examples of Outgoing Converter-Assisted Multipath
Multipath TCP Connection . . . . . . . . . . . . . . . . . 11 TCP Connections . . . . . . . . . . . . . . . . . . . . . 10
3.3. Differences with SOCKSv5 . . . . . . . . . . . . . . . . . 12 3.4. Sample Example of Incoming Converter-Assisted Multipath
4. The Converter Protocol . . . . . . . . . . . . . . . . . . . . 15 TCP Connection . . . . . . . . . . . . . . . . . . . . . 11
4.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 15 4. The Converter Protocol (Convert) . . . . . . . . . . . . . . 12
4.2. The Fixed Header . . . . . . . . . . . . . . . . . . . . . 15 4.1. The Convert Fixed Header . . . . . . . . . . . . . . . . 12
4.3. Transport Converter TLVs . . . . . . . . . . . . . . . . . 16 4.2. Convert TLVs . . . . . . . . . . . . . . . . . . . . . . 13
4.3.1. Connect TLV . . . . . . . . . . . . . . . . . . . . . 16 4.2.1. Generic Convert TLV Format . . . . . . . . . . . . . 13
4.3.2. Extended TCP Header TLV . . . . . . . . . . . . . . . 18 4.2.2. Summary of Supported Convert TLVs . . . . . . . . . . 14
4.3.3. Error TLV . . . . . . . . . . . . . . . . . . . . . . 19 4.2.3. The Bootstrap TLV . . . . . . . . . . . . . . . . . . 15
4.3.4. The Bootstrap TLV . . . . . . . . . . . . . . . . . . 21 4.2.4. Supported TCP Extension Services TLV . . . . . . . . 15
4.3.5. Supported TCP Options TLV . . . . . . . . . . . . . . 22 4.2.5. Connect TLV . . . . . . . . . . . . . . . . . . . . . 16
5. Interactions with middleboxes . . . . . . . . . . . . . . . . 23 4.2.6. Extended TCP Header TLV . . . . . . . . . . . . . . . 17
6. Security Considerations . . . . . . . . . . . . . . . . . . . 24 4.2.7. Error TLV . . . . . . . . . . . . . . . . . . . . . . 18
6.1. Privacy & Ingress Filtering . . . . . . . . . . . . . . . 24 5. Compatibility of Specific TCP Options with the Conversion
6.2. Authorization . . . . . . . . . . . . . . . . . . . . . . 24 Service . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
6.3. Denial of Service . . . . . . . . . . . . . . . . . . . . 24 5.1. Base TCP Options . . . . . . . . . . . . . . . . . . . . 21
6.4. Traffic Theft . . . . . . . . . . . . . . . . . . . . . . 25 5.2. Window Scale (WS) . . . . . . . . . . . . . . . . . . . . 21
6.5. Multipath TCP-specific Considerations . . . . . . . . . . 25 5.3. Selective Acknowledgements . . . . . . . . . . . . . . . 22
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 5.4. Timestamp . . . . . . . . . . . . . . . . . . . . . . . . 22
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28 5.5. Multipath TCP . . . . . . . . . . . . . . . . . . . . . . 23
8.1. Contributors . . . . . . . . . . . . . . . . . . . . . . . 28 5.6. TCP Fast Open . . . . . . . . . . . . . . . . . . . . . . 23
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29 5.7. TCP User Timeout . . . . . . . . . . . . . . . . . . . . 23
9.1. Normative References . . . . . . . . . . . . . . . . . . . 29 5.8. TCP-AO . . . . . . . . . . . . . . . . . . . . . . . . . 24
9.2. Informative References . . . . . . . . . . . . . . . . . . 29 5.9. TCP Experimental Options . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 33 6. Interactions with Middleboxes . . . . . . . . . . . . . . . . 24
7. Security Considerations . . . . . . . . . . . . . . . . . . . 25
7.1. Privacy & Ingress Filtering . . . . . . . . . . . . . . . 25
7.2. Authorization . . . . . . . . . . . . . . . . . . . . . . 25
7.3. Denial of Service . . . . . . . . . . . . . . . . . . . . 25
7.4. Traffic Theft . . . . . . . . . . . . . . . . . . . . . . 26
7.5. Multipath TCP-specific Considerations . . . . . . . . . . 26
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
8.1. Convert Service Port Number . . . . . . . . . . . . . . . 27
8.2. The Converter Protocol (Convert) Parameters . . . . . . . 27
8.2.1. Convert Versions . . . . . . . . . . . . . . . . . . 27
8.2.2. Convert TLVs . . . . . . . . . . . . . . . . . . . . 28
8.2.3. Convert Error Messages . . . . . . . . . . . . . . . 28
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 29
9.1. Contributors . . . . . . . . . . . . . . . . . . . . . . 30
10. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 30
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 30
11.1. Normative References . . . . . . . . . . . . . . . . . . 30
11.2. Informative References . . . . . . . . . . . . . . . . . 31
Appendix A. Differences with SOCKSv5 . . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 36
1. Introduction 1. Introduction
Transport protocols like TCP evolve regularly [RFC7414]. TCP has Transport protocols like TCP evolve regularly [RFC7414]. TCP has
been improved in different ways. Some improvements such as changing been improved in different ways. Some improvements such as changing
the initial window size or modifying the congestion control scheme the initial window size [RFC6928] or modifying the congestion control
can be applied independently on clients and servers. Other scheme can be applied independently on clients and servers. Other
improvements such as Selective Acknowledgements [RFC2018] or large improvements such as Selective Acknowledgements [RFC2018] or large
windows [RFC7323] require a new TCP option or to change the semantics windows [RFC7323] require a new TCP option or to change the semantics
of some fields in the TCP header. These modifications must be of some fields in the TCP header. These modifications must be
deployed on both clients and servers to be actually used on the deployed on both clients and servers to be actually used on the
Internet. Experience with the latter TCP extensions reveals that Internet. Experience with the latter TCP extensions reveals that
their deployment can require many years. Fukuda reports in their deployment can require many years. [Fukuda2011] reports
[Fukuda2011] results of a decade of measurements showing the results of a decade of measurements showing the deployment of
deployment of Selective Acknowledgements, Window Scale and TCP Selective Acknowledgements, Window Scale and TCP Timestamps.
Timestamps. Trammel et al. provide in [ANRW17] measurements showing [ANRW17] describes measurements showing that TCP Fast Open [RFC7413]
that TCP Fast Open [RFC7413] (TFO) is still not widely deployed. (TFO) is still not widely deployed.
There are some situations where the transport stack used on clients There are some situations where the transport stack used on clients
(resp. servers) can be upgraded at a faster pace than the transport (resp. servers) can be upgraded at a faster pace than the transport
stack running on servers (resp. clients). In those situations, stack running on servers (resp. clients). In those situations,
clients would typically want to benefit from the features of an clients would typically want to benefit from the features of an
improved transport protocol even if the servers have not yet been improved transport protocol even if the servers have not yet been
upgraded and conversely. In the past, Performance Enhancing Proxies upgraded and conversely. In the past, Performance Enhancing Proxies
have been proposed and deployed [RFC3135] as solutions to improve TCP have been proposed and deployed [RFC3135] as solutions to improve TCP
performance over links with specific characteristics. performance over links with specific characteristics.
Recent examples of TCP extensions include Multipath TCP [RFC6824] or Recent examples of TCP extensions include Multipath TCP
TCPINC [I-D.ietf-tcpinc-tcpcrypt]. Those extensions provide features [RFC6824][I-D.ietf-mptcp-rfc6824bis] or TCPINC
that are interesting for clients such as wireless devices. With [I-D.ietf-tcpinc-tcpcrypt]. Those extensions provide features that
Multipath TCP, those devices could seamlessly use WLAN and cellular are interesting for clients such as wireless devices. With Multipath
networks, for bonding purposes, faster handovers, or better TCP, those devices could seamlessly use WLAN and cellular networks,
resiliency. Unfortunately, deploying those extensions on both a wide for bonding purposes, faster handovers, or better resiliency.
range of clients and servers remains difficult. Unfortunately, deploying those extensions on both a wide range of
clients and servers remains difficult.
More recently, experimentation of 5G bonding, which has very scarce
coverage, has been conducted into global range of the incumbent 4G
(LTE) connectivity in newly devised clients using Multipath TCP
proxy. Even if the 5G and the 4G bonding by using Multipath TCP
increases the bandwidth to data transfer, it is as well crucial to
minimize latency for all the way between endhosts regardless of
whether intermediate nodes are inside or ouside of the mobile core.
In order to handle uRLLC (Ultra-Reliable Low-Latency Communication)
for the next generation mobile network, Multipath TCP and its proxy
mechanism must be optimized to reduce latency.
This document specifies an application proxy, called Transport This document specifies an application proxy, called Transport
Converter (TC). A Transport Converter is a function that is Converter. A Transport Converter is a function that is installed by
installed by a network operator to aid the deployment of TCP a network operator to aid the deployment of TCP extensions and to
extensions and to provide the benefits of such extensions to clients. provide the benefits of such extensions to clients. A Transport
A Transport Converter supports one or more TCP extensions. The Converter may support conversion service for one or more TCP
Converter Protocol (CP) is an application layer protocol that uses a extensions. This service is provided by means of the Converter
TCP port number (see IANA section). The Transport Converter adheres Protocol (Convert), that is an application layer protocol which uses
to the main principles as drawn in [RFC1919]. In particular, the TBA TCP port number (Section 8).
Converter achieves the following:
The Transport Converter adheres to the main principles as drawn in
[RFC1919]. In particular, the Converter achieves the following:
o Listen for client sessions; o Listen for client sessions;
o Receive from a client the address of the final target server; o Receive from a client the address of the final target server;
o Setup a session to the final server; o Setup a session to the final server;
o Relay control messages and data between the client and the server; o Relay control messages and data between the client and the server;
o Perform access controls according to local policies. o Perform access controls according to local policies.
The main advantage of network-assisted converters is that they enable The main advantage of network-assisted Converters is that they enable
new TCP extensions to be used on a subset of the end-to-end path, new TCP extensions to be used on a subset of the end-to-end path,
which encourages the deployment of these extensions. The Transport which encourages the deployment of these extensions. The Transport
Converter allows the client and the server to directly negotiate some Converter allows the client and the server to directly negotiate TCP
options between the endpoints. This document focuses on Multipath options.
TCP [RFC6824] and TCP Fast Open [RFC7413]. The support for other TCP
extensions will be discussed in other documents. The Convert Protocol is a generic mechanism to provide 0-RTT
conversion service. As a sample applicability use case, this
document specifies how the Convert Protocol applies for Multiptah
TCP. It is out of scope of this document to provide a comprehensive
list of potential all conversion services; separate documents may be
edited in the future for other conversion services upon need.
This document does not assume that all the traffic is eligible to the This document does not assume that all the traffic is eligible to the
network-assisted conversion service. Only a subset of the traffic network-assisted conversion service. Only a subset of the traffic
will be forwarded to a converter according to a set of policies. will be forwarded to a Converter according to a set of policies.
Furthermore, it is possible to bypass the converter to connect to the Furthermore, it is possible to bypass the Converter to connect to the
servers that already support the required TCP extension. servers that already support the required TCP extension.
This document assumes that a client is configured with one or a list This document assumes that a client is configured with one or a list
of transport converters. Configuration means are outside the scope of Converters. Configuration means are outside the scope of this
of this document. document.
This document is organized as follows. We first provide a brief This document is organized as follows. We first provide a brief
explanation of the operation of Transport Converters in Section 3. explanation of the operation of Transport Converters in Section 3.
We compare them in Section 3.3 with SOCKS proxies that are already We describe the Converter Protocol in Section 4. We discuss in
used to deploy Multipath TCP in cellular networks [IETFJ16]. We then Section 5 how Transport Converters can be used to support different
describe the Converter Protocol in Section 4. We then discuss the TCP options. We then discuss the interactions with middleboxes
interactions with middleboxes (Section 5) and the security (Section 6) and the security considerations (Section 7).
considerations (Section 6).
2. Applicability Scope Appendix A provides a comparison with SOCKS proxies that are already
used to deploy Multipath TCP in some cellular networks.
This specification is designed with Multipath TCP 2. Requirements
[RFC6824][I-D.ietf-mptcp-rfc6824bis] and TCP Fast Open [RFC7413] in
mind. That is, the specification draws how network-assisted The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
Multipath TCP connections can be established even if the remote "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
server is not Multipath TCP-capable without inducing extra connection "OPTIONAL" in this document are to be interpreted as described in
delays (0-RTT proxy). Further, the specification allows the client [RFC2119] [RFC8174] when, and only when, they appear in all capitals,
for end-to-end Multipath TCP connections with or without proxy as shown here.
involvement. Assessing the applicability of the solution to other
use cases and other TCP extensions such as [I-D.ietf-tcpinc-tcpcrypt]
is outside the scope of this document. Future documents are required
to specify the exact behavior when the converter is deployed in other
contexts than Multipath TCP.
3. Architecture 3. Architecture
3.1. Functional Elements
The architecture considers three types of endhosts: The architecture considers three types of endhosts:
o Client endhosts; o Client endhosts;
o Transport Converters; o Transport Converters;
o Server endhosts. o Server endhosts.
It does not mandate anything on the server side. The architecture
assumes that new software will be installed on the Client hosts and
on Transport Converters. Further, the architecture allows for making
use of TCP new extensions if those are supported by a given server.
A Transport Converter is a network function that relays all data A Transport Converter is a network function that relays all data
exchanged over one upstream connection to one downstream connection exchanged over one upstream connection to one downstream connection
and vice versa. A connection can be initiated from both interfaces and vice versa (Figure 1). The Converter, thus, maintains state that
of the transport converter (Internet-facing interface, client-facing associates one upstream connection to a corresponding downstream
interface). The converter, thus, maintains state that associates one connection.
upstream connection to a corresponding downstream connection. One of
the benefits of this design is that different transport protocol A connection can be initiated from both sides of the Transport
extensions can be used on the upstream and the downstream Converter (Internet-facing interface, client-facing interface).
connections. This encourages the deployment of new TCP extensions
until they are supported by many servers.
+------------+ +------------+
<--- upstream --->| Transport |<--- downstream ---> <--- upstream --->| Transport |<--- downstream --->
| Converter | | Converter |
+------------+ +------------+
Figure 1: A Transport Converter relays data between pairs of TCP Figure 1: A Transport Converter relays data between pairs of TCP
connections connections
Transport converters can be operated by network operators or third Transport Converters can be operated by network operators or third
parties. The Client is configured, through means that are outside parties. Nevertheless, this document focuses on the single
the scope of this document, with the names and/or the addresses of administrative deployment case where the entity offering the
one or more Transport Converters. The packets belonging to the pair connectivity service to a client is also the entity which owns and
of connections between the Client and Server passing through a operates the Transport Converter.
Transport Converter may follow a different path than the packets
directly exchanged between the Client and the Server. Deployments
should minimize the possible additional delay by carefully selecting
the location of the Transport Converter used to reach a given
destination.
A transport converter can be embedded in a standalone device or be A Transport Converter can be embedded in a standalone device or be
activated as a service on a router. How such function is enabled is activated as a service on a router. How such function is enabled is
deployement-specific. deployment-specific (Figure 2).
+-+ +-+ +-+ +-+ +-+ +-+
Client - |R| -- |R| -- |R| - - - Server Client - |R| -- |R| -- |R| - - - Server
+-+ +-+ +-+ +-+ +-+ +-+
| |
Transport Transport
Converter Converter
Figure 2: A Transport Converter can be installed anywhere in the Figure 2: A Transport Converter can be installed anywhere in the
network network
When establishing a connection, the Client can, depending on local The architecture assumes that new software will be installed on the
policies, either contact the Server directly (e.g., by sending a TCP Client hosts and on Transport Converters. Further, the architecture
SYN towards the Server) or create the connection via a Transport allows for making use of TCP new extensions if those are supported by
Converter. In the latter case, which is the case we consider in this a given server.
document, the Client initiates a connection towards the Transport
Converter and indicates the address and port number of the ultimate
Server inside the connection establishment packet. Doing so enables
the Transport Converter to immediately initiate a connection towards
that Server, without experiencing an extra delay. The Transport
Converter waits until the confirmation that the Server agrees to
establish the connection before confirming it to the Client.
The client places the destination address and port number of the The Client is configured, through means that are outside the scope of
target Server in the payload of the SYN sent to the Converter by this document, with the names and/or the addresses of one or more
leveraging TCP Fast Open [RFC7413]. In accordance with [RFC1919], Transport Converters.
the Transport Converter maintains two connections that are combined
together. The upstream connection is the one between the Client and The architecture does not mandate anything on the server side.
the Transport Converter. The downstream connection is between the
Transport Converter and the remote Server. Any user data received by One of the benefits of this design is that different transport
the Transport Converter over the upstream (resp., downstream) protocol extensions can be used on the upstream and the downstream
connection is relayed over the downstream (resp., upstream) connections. This encourages the deployment of new TCP extensions
connection. until they are widely supported by servers.
3.2. Theory of Operation
At a high level, the objective of the Transport Converter is to allow At a high level, the objective of the Transport Converter is to allow
the Client to use a specific extension, e.g. Multipath TCP, on a the Client to use a specific extension, e.g. Multipath TCP, on a
subset of the end-to-end path even if the Server does not support subset of the end-to-end path even if the Server does not support
this extension. This is illustrated in Figure 3 where the Client this extension. This is illustrated in Figure 3 where the Client
initiates a Multipath TCP connection with the Converter (Multipath initiates a Multipath TCP connection with the Converter (Multipath
packets are shown with =) while the Converter uses a regular TCP packets are shown with "===") while the Converter uses a regular TCP
connection with the Server. connection with the Server.
The packets belonging to the pair of connections between the Client
and Server passing through a Transport Converter may follow a
different path than the packets directly exchanged between the Client
and the Server. Deployments should minimize the possible additional
delay by carefully selecting the location of the Transport Converter
used to reach a given destination.
Transport Transport
Client Converter Server Client Converter Server
======================> ======================>
--------------------> -------------------->
<-------------------- <--------------------
<====================== <======================
Multipath TCP packets Regular TCP packets Multipath TCP packets Regular TCP packets
Figure 3: Different TCP variants can be used on the Client-Converter Figure 3: Different TCP variants can be used on the Client-Converter
path and on the Converter-Server path path and on the Converter-Server path
When establishing a connection, the Client can, depending on local
policies, either contact the Server directly (e.g., by sending a TCP
SYN towards the Server) or create the connection via a Transport
Converter. In the latter case, which is the case we consider in this
document, the Client initiates a connection towards the Transport
Converter and indicates the IP address and port number of the
ultimate Server inside the connection establishment packet. Doing so
enables the Transport Converter to immediately initiate a connection
towards that Server, without experiencing an extra delay. The
Transport Converter waits until the confirmation that the Server
agrees to establish the connection before confirming it to the
Client.
The client places the destination address and port number of the
target Server in the payload of the SYN sent to the Converter by
leveraging TCP Fast Open [RFC7413]. In accordance with [RFC1919],
the Transport Converter maintains two connections that are combined
together:
o the upstream connection is the one between the Client and the
Transport Converter.
o the downstream connection is between the Transport Converter and
the remote Server.
Any user data received by the Transport Converter over the upstream
(resp., downstream) connection is relayed over the downstream (resp.,
upstream) connection.
Figure 4 illustrates the establishment of a TCP connection by the Figure 4 illustrates the establishment of a TCP connection by the
Client through a Transport Converter. The information shown between Client through a Transport Converter. The information shown between
brackets is part of the Converter protocol described later in this brackets is part of the Converter Protocol described later in this
document. document.
The Client sends a SYN destined to the Transport Converter. This SYN
contains a TFO Cookie and inside its payload the addresses and ports
of the destination Server. The Transport Converter does not reply
immediately to this SYN. It first tries to create a TCP connection
towards the destination Server. If this second connection succeeds,
the Transport Converter confirms the establishment of the connection
to the Client by returning a SYN+ACK and the first bytes of the
bytestream contain information about the TCP Options that were
negotiated with the final Server. This information is sent at the
beginning of the bytestream, either directly in the SYN+ACK or in a
subsequent packet. For graphical reasons, the figures in this
section show that the Converter returns this information in the SYN+
ACK packet. An implementation could also place this information in a
packet that it sent shortly after the SYN+ACK.
Transport Transport
Client Converter Server Client Converter Server
--------------------> -------------------->
SYN TFO [->Server:port] SYN TFO [->Server:port]
--------------------> -------------------->
SYN SYN
<-------------------- <--------------------
SYN+ACK SYN+ACK
<-------------------- <--------------------
SYN+ACK [ ] SYN+ACK [ ]
Figure 4: Establishment of a TCP connection through a Converter Figure 4: Establishment of a TCP connection through a Converter
The Client sends a SYN destined to the Transport Converter. This SYN
contains a TFO cookie and inside its payload the addresses and ports
of the destination Server. The Transport Converter does not reply
immediately to this SYN. It first tries to create a TCP connection
towards the destination Server. If this second connection succeeds,
the Transport Converter confirms the establishment of
the connection to the Client by returning a SYN+ACK and the first
bytes of the bytestream contain information about the TCP options
that were negotiated with the final Server. This information is sent
at the beginning of the bytestream, either directly in the SYN+ACK or
in a subsequent packet. For graphical reasons, the figures in this
section show that the Converter returns this information in the
SYN+ACK packet. An implementation could also place this information
in a packet that it sent shortly after the SYN+ACK.
The connection can also be established from the Internet towards a The connection can also be established from the Internet towards a
client via a transport converter. This is typically the case when Client via a Transport Converter. This is typically the case when
the client embeds a server (video server, for example). the Client embeds a server (video server, for example).
The procedure described in Figure 4 assumes that the Client has The procedure described in Figure 4 assumes that the Client has
obtained a TFO Cookie from the Transport Converter. This is part of obtained a TFO cookie from the Transport Converter. This is part of
the Bootstrap procedure which is illustrated in Figure 5. The Client the Bootstrap procedure which is illustrated in Figure 5. The Client
sends a SYN with a TFO Request option to obtain a valid cookie from sends a SYN with a TFO request option to obtain a valid cookie from
the Converter. The Converter replies with a TFO cookie in the SYN+ the Converter. The Converter replies with a TFO cookie in the
ACK. Once this connection has been established, the Client sends a SYN+ACK. Once this connection has been established, the Client sends
Bootstrap message to request the list of TCP options supported by the a Bootstrap message to request the list of TCP options for which the
Transport Converter. Thanks to this procedure, the Client knows Transport Converter provides a conversion service.
which TCP options are supported by a given Transport Converter.
Transport Transport
Client Converter Server Client Converter Server
--------------------> -------------------->
SYN TFO(empty) SYN TFO(empty)
<-------------------- <--------------------
SYN+ACK TFO(cookie) SYN+ACK TFO(cookie)
--------------------> -------------------->
[Bootstrap] [Bootstrap]
<-------------------- <--------------------
[Supported TCP Options] [Supported TCP Extension Services]
Figure 5: Bootstrapping a Client connection to a Transport Converter Figure 5: Bootstrapping a Client connection to a Transport Converter
Note that the Converter may rely on local policies to decide whether Note that the Converter may rely on local policies to decide whether
it can service a given requesting client. That is, the Converter may it can service a given requesting Client. That is, the Converter
not return a cookie for that client. will not return a cookie for that Client. How such policies are
supplied to the Converter are out of scope.
Also, the Converter may behave in a Cookie-less mode when appropriate Also, the Converter may behave in a cookie-less mode when appropriate
means are enforced at the converter and the network in-between to means are enforced at the Converter and the network in-between to
protect against attacks such as spoofing and SYN flood. Under such protect against attacks such as spoofing and SYN flood. Under such
deployments, the use of TFO is not required. deployments, the use of TFO is not required.
3.1. Sample Examples of Converter-Assisted Multipath TCP Connections 3.3. Sample Examples of Outgoing Converter-Assisted Multipath TCP
Connections
As an example, let us consider how such a protocol can help the As an example (Figure 6), let us consider how the Convert protocol
deployment of Multipath TCP [RFC6824]. We assume that both the can help the deployment of Multipath TCP [RFC6824]. We assume that
Client and the Transport Converter support Multipath TCP, but both the Client and the Transport Converter support Multipath TCP,
consider two different cases depending but consider two different cases depending whether the Server
whether the Server supports Multipath TCP or not. A Multipath TCP supports Multipath TCP or not. A Multipath TCP connection is created
connection is created by placing the MP_CAPABLE (MPC) option in the by placing the MP_CAPABLE (MPC) option in the SYN sent by the Client.
SYN sent by the Client.
Figure 6 describes the operation of the Transport Converter if the Figure 6 describes the operation of the Transport Converter if the
Server does not support Multipath TCP. Server does not support Multipath TCP.
Transport Transport
Client Converter Server Client Converter Server
--------------------> -------------------->
SYN, MPC [->Server:port] SYN, MPC [->Server:port]
--------------------> -------------------->
skipping to change at page 10, line 40 skipping to change at page 10, line 48
Figure 6: Establishment of a Multipath TCP connection through a Figure 6: Establishment of a Multipath TCP connection through a
Converter Converter
The Client tries to initiate a Multipath TCP connection by sending a The Client tries to initiate a Multipath TCP connection by sending a
SYN with the MP_CAPABLE option (MPC in Figure 6). The SYN includes SYN with the MP_CAPABLE option (MPC in Figure 6). The SYN includes
the address and port number of the final Server and the Transport the address and port number of the final Server and the Transport
Converter attempts to initiate a Multipath TCP connection towards Converter attempts to initiate a Multipath TCP connection towards
this Server. Since the Server does not support Multipath TCP, it this Server. Since the Server does not support Multipath TCP, it
replies with a SYN+ACK that does not contain the MP_CAPABLE option. replies with a SYN+ACK that does not contain the MP_CAPABLE option.
The Transport Converter notes that the connection with the Server The Transport Converter notes that the connection with the Server
does not support Multipath TCP and returns the TCP Options received does not support Multipath TCP and returns the TCP options received
from the Server to the Client. from the Server to the Client.
Figure 7 considers a Server that supports Multipath TCP. In this Figure 7 considers a Server that supports Multipath TCP. In this
case, it replies to the SYN sent by the Transport Converter with the case, it replies to the SYN sent by the Transport Converter with the
MP_CAPABLE option. Upon reception of this SYN+ACK, the Transport MP_CAPABLE option. Upon reception of this SYN+ACK, the Transport
Converter confirms the establishment of the connection to the Client Converter confirms the establishment of the connection to the Client
and indicates to the Client that the Server supports Multipath TCP. and indicates to the Client that the Server supports Multipath TCP.
With this information, the Client has discovered that the Server With this information, the Client has discovered that the Server
supports Multipath TCP natively. This will enable it to bypass the supports Multipath TCP natively. This will enable it to bypass the
Transport Converter for the next Multipath TCP connection that it Transport Converter for the next Multipath TCP connection that it
skipping to change at page 11, line 27 skipping to change at page 11, line 36
SYN+ACK, MPC [ MPC supported ] SYN+ACK, MPC [ MPC supported ]
--------------------> -------------------->
ACK, MPC ACK, MPC
--------------------> -------------------->
ACK, MPC ACK, MPC
Figure 7: Establishment of a Multipath TCP connection through a Figure 7: Establishment of a Multipath TCP connection through a
converter converter
3.2. Sample Example of Incoming Converter-Assisted Multipath TCP 3.4. Sample Example of Incoming Converter-Assisted Multipath TCP
Connection Connection
An example of an incoming converter-assisted Multipath TCP connection An example of an incoming Converter-assisted Multipath TCP connection
is depicted in Figure 8. In order to support incoming connections is depicted in Figure 8. In order to support incoming connections
from remote hosts, the client may use PCP [RFC6887] to instruct the from remote hosts, the Client may use PCP [RFC6887] to instruct the
converter to create dynamic mappings. Those mappings will be used by Converter to create dynamic mappings. Those mappings will be used by
the converter to intercept an incoming TCP connection destined to the the Converter to intercept an incoming TCP connection destined to the
client and convert it into a Multipath TCP connection. Client and convert it into a Multipath TCP connection.
Transport Transport
H1 Converter Remote Host Client Converter Remote Host
<------------------- <-------------------
SYN SYN
<------------------- <-------------------
SYN, MPC[Remote Host:port] SYN, MPC[Remote Host:port]
---------------------> --------------------->
SYN+ACK, MPC SYN+ACK, MPC
---------------------> --------------------->
SYN+ACK SYN+ACK
<--------------------- <---------------------
ACK ACK
<------------------- <-------------------
ACK, MPC ACK, MPC
Figure 8: Establishment of an Incoming TCP Connection through a Figure 8: Establishment of an Incoming TCP Connection through a
Converter Converter
3.3. Differences with SOCKSv5 4. The Converter Protocol (Convert)
The description above is a simplified description of the Converter This section describes in details the messages that are exchanged
protocol. At a first glance, the proposed solution could seem between a Client and a Transport Converter. The Converter Protocol
similar to the SOCKS v5 protocol [RFC1928]. This protocol is used to (Convert, for short) leverages the TCP Fast Open extension [RFC7413].
proxy TCP connections. The Client creates a connection to a SOCKS
proxy, exchanges authentication information and indicates the
destination address and port of the final server. At this point, the
SOCKS proxy creates a connection towards the final server and relays
all data between the two proxied connections. The operation of an
implementation based on SOCKSv5 is illustrated in Figure 9.
Client SOCKS Proxy Server The Converter Protocol uses a 32 bits long fixed header that is sent
--------------------> by both the Client and the Transport Converter. This header
SYN indicates both the version of the protocol used and the length of the
<-------------------- Convert message.
SYN+ACK
-------------------->
ACK
--------------------> 4.1. The Convert Fixed Header
Version=5, Auth Methods
<--------------------
Method
-------------------->
Auth Request (if "No auth" method negotiated)
<--------------------
Auth Response
-------------------->
Connect Server:Port -------------------->
SYN
<-------------------- The Fixed Header is used to exchange information about the version
SYN+ACK and length of the messages between the Client and the Transport
<-------------------- Converter.
Succeeded
--------------------> The Client and the Transport Converter MUST send the fixed-sized
Data1 header shown in Figure 9 as the first four bytes of the bytestream.
-------------------->
Data1
<-------------------- 1 2 3
Data2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
<-------------------- +---------------+---------------+-------------------------------+
Data2 | Version | Total Length | Unassigned |
+---------------+---------------+-------------------------------+
Figure 9: Establishment of a TCP connection through a SOCKS proxy Figure 9: The fixed-sized header of the Converter protocol
without authentication
The Converter protocol also relays data between an upstream and a The Version is encoded as an 8 bits unsigned integer value. This
downstream connection, but there are important differences with document specifies version 1. Version 0 is reserved by this document
SOCKSv5. and MUST NOT be used.
A first difference is that the Converter protocol leverages the TFO The Total Length is the number of 32 bits word, including the header,
option [RFC7413] to exchange all control information during the of the bytestream that are consumed by the Converter protocol
three-way handshake. This reduces the connection establishment delay messages. Since Total Length is also an 8 bits unsigned integer,
compared to SOCKS that requires two or more round-trip-times before those messages cannot consume more than 1020 bytes of data. This
the establishment of the downstream connection towards the final limits the number of bytes that a Transport Converter needs to
destination. In today's Internet, latency is a important metric and process. A Total Length of zero is invalid and the connection MUST
various protocols have been tuned to reduce their latency be reset upon reception of such a header.
[I-D.arkko-arch-low-latency]. A recently proposed extension to SOCKS
also leverages the TFO option [I-D.olteanu-intarea-socks-6].
A second difference is that the Converter protocol explicitly takes The Unassigned field MUST be set to zero in this version of the
the TCP extensions into account. By using the Converter protocol, protocol. These bits are available for future use [RFC8126].
the Client can learn whether a given TCP extension is supported by
the destination Server. This enables the Client to bypass the
Transport Converter when the destination supports the required TCP
extension. Neither SOCKS v5 [RFC1928] nor the proposed SOCKS v6
[I-D.olteanu-intarea-socks-6] provide such a feature.
A third difference is that a Transport Converter will only accept the 4.2. Convert TLVs
connection initiated by the Client provided that the downstream
connection is accepted by the Server. If the Server refuses the
connection establishment attempt from the Transport Converter, then
the upstream connection from the Client is rejected as well. This
feature is important for applications that check the availability of
a Server or use the time to connect as a hint on the selection of a
Server [RFC6555].
4. The Converter Protocol 4.2.1. Generic Convert TLV Format
We now describe in details the messages that are exchanged between a The Convert protocol uses variable length messages that are encoded
Client and a Transport Converter. The Converter Protocol (CP) using the generic TLV format depicted in Figure 10. All TLV fields
leverages the TCP Fast Open extension defined in [RFC7413]. are encoded using the network byte order.
The Converter Protocol uses a 32 bits long fixed header that is sent 1 2 3
by both the Client and the Transport Converter. This header 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
indicates both the version of the protocol used and the length of the +---------------+---------------+-------------------------------+
CP message. | Type | Length | (optional) Value ... |
+---------------+---------------+-------------------------------+
| ... (optional) Value |
+---------------------------------------------------------------+
4.1. Requirements Figure 10: Converter Generic TLV Format
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", A given TLV MUST only appear once on a connection. If two or more
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and instances of the same TLV are exchanged over a Converter connection,
"OPTIONAL" in this document are to be interpreted as described in the associated TCP connections MUST be closed.
[RFC2119] [RFC8174] when, and only when, they appear in all capitals,
as shown here.
4.2. The Fixed Header 4.2.2. Summary of Supported Convert TLVs
The Fixed Header is used to exchange information about the version This document specifies the following Convert TLVs:
and length of the messages between the Client and the Transport
Converter. The Client and the Transport Converter MUST send the +------+-----+----------+------------------------------------------+
fixed-sized header shown in Figure 10 as the first four bytes of the | Type | Hex | Length | Description |
bytestream. +------+-----+----------+------------------------------------------+
| 1 | 0x1 | 1 | Bootstrap TLV |
| 10 | 0xA | Variable| Connect TLV |
| 20 | 0x14| Variable| Extended TCP Header TLV |
| 21 | 0x15| Variable| Supported TCP Extension Services TLV |
| 30 | 0x1E| Variable| Error TLV |
+------+-----+----------+------------------------------------------+
Figure 11: The TLVs used by the Converter protocol
To establish a connection via a Transport Converter, a Client MUST
first obtain a valid TFO cookie from that Converter. This is the
bootstrap procedure during which the Client opens a connection to the
Transport Converter with an empty TFO option. According to
[RFC7413], the Transport Converter returns its cookie in the SYN+ACK.
Then the Client sends a Bootstrap TLV (Section 4.2.3) to which the
Transport Converter replies with the Supported TCP Extension Services
TLV described in Section 4.2.4.
With the TFO cookie of the Transport Converter, the Client can
request the establishment of connections to remote servers with the
Connect TLV (see Section 4.2.5). If the connection can be
established with the final server, the Transport Converter replies
with the Extended TCP Header TLV and returns an Error TLV inside a
RST packet (see Section 4.2.7).
When the Transport Converter receives an incoming connection
establishment from a Client, it MUST process the TCP options found in
the SYN and the Connect TLV. In general, the Transport Converter
MUST add to the proxied SYN the TCP options that were included in the
Connect TLV. It SHOULD add to the proxied SYN the TCP options that
were included in the incoming SYN provided that it supports the
corresponding TCP extension.
There are some exceptions to these rules given the semantics of some
TCP options. First, TCP options with Kinds 0 (EOL), 1 (NOP), 2
(MSS), and 3 (WS) MUST be used according to the configuration of the
TCP stack of the Transport Converter. The Timestamps option
(Kind=10) SHOULD be used in the proxied SYN if it was present in the
incoming SYN, but the contents of the option in the proxied SYN
SHOULD be set by the Converter's stack. The MP_CAPABLE option SHOULD
be added to the proxied SYN if it was present in the incoming SYN,
but the content of the option in the proxied SYN SHOULD be set by the
Converter's stack. The TCP Fast Open cookie option SHOULD be handled
as described in Section 6.
As a general rule, when an error is encountered an Error TLV with the
appropriate error code MUST be returned.
4.2.3. The Bootstrap TLV
The Bootstrap TLV (Figure 12 is sent by a Client to request the TCP
extensions that are supported by a Transport Converter and for which
it provides a conversion service. It is typically sent on the first
connection that a Client establishes with a Transport Converter to
learn its capabilities. Assuming a Client is entitled to invoke the
Converter, this latter replies with the Supported TCP Extensions
Services TLV described in Section 4.2.4.
1 2 3 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+-------------------------------+ +---------------+---------------+-------------------------------+
| Version | Total Length | Reserved | | Type | Length | Zero |
+---------------+---------------+-------------------------------+ +---------------+---------------+-------------------------------+
Figure 10: The fixed-sized header of the Converter protocol Figure 12: The Bootstrap TLV
The Version is encoded as an 8 bits unsigned integer value. This
document specifies version 1. The Total Length is the number of 32
bits word, including the header, of the bytestream that are consumed
by the Converter protocol messages. Since Total Length is also an 8
bits unsigned integer, those messages cannot consume more than 1020
bytes of data. This limits the number of bytes that a Transport
Converter needs to process. A Total Length of zero is invalid and
the connection MUST be reset upon reception of such a header. The
Reserved field MUST be set to zero in this version of the protocol.
4.3. Transport Converter TLVs 4.2.4. Supported TCP Extension Services TLV
The Converter protocol uses variable length messages that are encoded The Supported TCP Extension Services TLV (Figure 13) is used by a
using a TLV format to simplify the parsing of the messages and leave Converter to announce the TCP options for which it provides a
room to extend the protocol in the future. A given TLV can only conversion service. Each supported TCP option is encoded with its
appear once on a connection. If two or more copies of the same TLV TCP option Kind listed in the "TCP Parameters" registry maintained by
are exchanged over a Converter connection, the associated TCP IANA.
connections MUST be closed. All fields are encoded using the network
byte order.
Five TLVs are defined in this document. They are listed in Table 1. 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+-------------------------------+
| Type | Length | Unassigned |
+---------------+---------------+-------------------------------+
| Kind #1 | Kind #2 | ... |
+---------------+---------------+-------------------------------+
/ ... /
/ /
+---------------------------------------------------------------+
+------+------+----------+---------------------------+ Figure 13: The Supported TCP Extension Services TLV
| Type | Hex | Length | Description |
+------+------+----------+---------------------------+
| 1 | 0x1 | 1 | Bootstrap TLV |
| | | | |
| 10 | 0xA | Variable | Connect TLV |
| | | | |
| 20 | 0x14 | Variable | Extended TCP Header TLV |
| | | | |
| 21 | 0x15 | Variable | Supported TCP Options TLV |
| | | | |
| 30 | 0x1E | Variable | Error TLV |
+------+------+----------+---------------------------+
Table 1: The TLVs used by the Converter protocol TCP option Kinds 0, 1, and 2 defined in [RFC0793] are supported by
all TCP implementations and thus MUST NOT appear in this list.
To use a given Transport Converter, a Client MUST first obtain a The list of Supported TCP Extension Services is padded with 0 to end
valid TFO cookie from it. This is the bootstrap procedure during on a 32 bits boundary.
which the Client opens a connection to the Transport Converter with
an empty TFO option. According to [RFC7413], the Transport Converter
returns its cookie in the SYN+ACK. Then the Client sends a Bootstrap
TLV and the Transport Converter replies with the Supported TCP
Options TLV that lists the TCP options that it supports (section
Section 4.3.5).
With the TFO Cookie of the Transport Converter, the Client can Typically, if the Converter only supports Multipath TCP conversion
request the establishment of connections to remote servers with the service, solely Kind=30 will be present in the Supported TCP
Connect TLV (see Section 4.3.1). If the connection can be Extension Services TLV returned by the Converter to a requesting
established with the final server, the Transport Converter replies Client.
with the Extended TCP Header TLV and returns an Error TLV inside a
RST packet (see section Section 4.3.3).
4.3.1. Connect TLV 4.2.5. Connect TLV
This TLV (Figure 11) is used to request the establishment of a The Connect TLV (Figure 14) is used to request the establishment of a
connection via a Transport Converter. connection via a Transport Converter.
The 'Remote Peer Port' and 'Remote Peer IP Address' fields contain The 'Remote Peer Port' and 'Remote Peer IP Address' fields contain
the destination port and IP address of the target server for an the destination port and IP address of the target server for an
outgoing connection towards a server located on the Internet. For outgoing connection towards a server located on the Internet. For
incoming connections destined to a client serviced via a Converter, incoming connections destined to a client serviced via a Converter,
these fields convey the source port and IP address. these fields convey the source port and IP address.
The Remote Peer IP Address MUST be encoded as an IPv6 address. IPv4 The Remote Peer IP Address MUST be encoded as an IPv6 address. IPv4
addresses MUST be encoded using the IPv4-Mapped IPv6 Address format addresses MUST be encoded using the IPv4-Mapped IPv6 Address format
skipping to change at page 17, line 35 skipping to change at page 16, line 51
+---------------+---------------+-------------------------------+ +---------------+---------------+-------------------------------+
| | | |
| Remote Peer IP Address (128 bits) | | Remote Peer IP Address (128 bits) |
| | | |
| | | |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
| TCP Options (Variable) | | TCP Options (Variable) |
| ... | | ... |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
Figure 11: The Connect TLV Figure 14: The Connect TLV
The 'TCP Options' field is a variable length field that carries a The 'TCP Options' field is a variable length field that carries a
list of TCP Option fields (Figure 12). Each TCP Option field is list of TCP option fields (Figure 15). Each TCP option field is
encoded as a block of 2+n bytes where the first byte is the TCP encoded as a block of 2+n bytes where the first byte is the TCP
Option Type and the second byte is the length of the TCP Option as option Type and the second byte is the length of the TCP option as
specified in [RFC0793]. The minimum value for the TCP Option Length specified in [RFC0793]. The minimum value for the TCP option Length
is 2. The TCP Options that do not include a length subfield, i.e., is 2. The TCP options that do not include a length subfield, i.e.,
option types 0 (EOL) and 1 (NOP) defined in [RFC0793] cannot be option types 0 (EOL) and 1 (NOP) defined in [RFC0793] cannot be
placed inside the TCP Options field of the Connect TLV. The optional placed inside the TCP options field of the Connect TLV. The optional
Value field contains the variable-length part of the TCP option. A Value field contains the variable-length part of the TCP option. A
length of two indicates the absence of the Value field. The TCP length of two indicates the absence of the Value field. The TCP
Options field always ends on a 32 bits boundary after being padded options field always ends on a 32 bits boundary after being padded
with zeros. with zeros.
1 2 3 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| TCPOpt type | TCPOpt Length | Value (opt) | .... | | TCPOpt type | TCPOpt Length | Value (opt) | .... |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| .... | | .... |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
| ... | | ... |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
Figure 12: The TCP Options field Figure 15: The TCP Options field
If a Transport Converter receives a Connect TLV with a non-empty TCP If a Transport Converter receives a Connect TLV with a non-empty TCP
Options field, it shall present those options to the destination peer options field, and the Converter accets to process the request, it
in addition to the TCP Options that it would have used according to SHALL present those options to the destination peer in addition to
its local policies. For the TCP Options that are listed without an the TCP options that it would have used according to its local
optional value, the Converter MUST generate its own value. For the policies. For the TCP options that are listed without an optional
TCP Options that are included in the 'TCP Options' field with an value, the Converter MUST generate its own value. For the TCP
optional value, it shall copy the entire option for use in the options that are included in the 'TCP Options' field with an optional
connection with the destination peer. This feature is required to value, it SHALL copy the entire option for use in the connection with
support TCP Fast Open. the destination peer. This feature is required to support TCP Fast
Open.
4.3.2. Extended TCP Header TLV The Converter may discard a Connect TLV request for many reasons
(e.g., bad TFO cookie, authorization failed, out of resources). An
error message indicating the encountered error is returned to the
requesting Client Section 4.2.7. In order to prevent denial-of-
service attacks, error messages sent to a Client SHOULD be rate-
limited.
The Extended TCP Header TLV is used by the Transport Converter to 4.2.6. Extended TCP Header TLV
send to the Client the extended TCP header that was returned by the
Server in the SYN+ACK packet. This TLV is only sent if the Client The Extended TCP Header TLV (Figure 16) is used by the Transport
sent a Connect TLV to request the establishment of a connection. Converter to send to the Client the extended TCP header that was
returned by the Server in the SYN+ACK packet. This TLV is only sent
if the Client sent a Connect TLV to request the establishment of a
connection.
1 2 3 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+-------------------------------+ +---------------+---------------+-------------------------------+
| Type | Length | Reserved | | Type | Length | Unassigned |
+---------------+---------------+-------------------------------+ +---------------+---------------+-------------------------------+
| Returned Extended TCP header | | Returned Extended TCP header |
| ... | | ... |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
Figure 13: The Extended TCP Header TLV Figure 16: The Extended TCP Header TLV
The Returned Extended TCP header field is a copy of the extended The Returned Extended TCP header field is a copy of the extended
header that was received in the SYN+ACK by the Transport Converter. header that was received in the SYN+ACK by the Transport Converter.
The Reserved field is set to zero by the transmitter and ignored by
the receiver.
4.3.3. Error TLV The Unassigned field MUST be set to zero by the transmitter and
ignored by the receiver. These bits are available for future use
[RFC8126].
This optional TLV can be used by the Transport Converter to provide 4.2.7. Error TLV
information about some errors that occurred during the processing of
a request to convert a connection. This TLV appears after the The optional Error TLV (Figure 17) can be used by the Transport
Converter header in a RST segment returned by the Transport Converter Converter to provide information about some errors that occurred
if the error is fatal and prevented the establishment of the during the processing of a request to convert a connection. This TLV
connection. If the error is not fatal and the connection could be appears after the Convert header in a RST segment returned by the
established with the final destination, then the error TLV will be Transport Converter if the error is fatal and prevented the
carried in the payload. establishment of the connection. If the error is not fatal and the
connection could be established with the final destination, then the
error TLV will be carried in the payload.
1 2 3 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+----------------+--------------+ +---------------+---------------+----------------+--------------+
| Type | Length | Error | Value | | Type | Length | Error | Value |
+---------------+---------------+----------------+--------------+ +---------------+---------------+----------------+--------------+
Figure 14: The Error TLV Figure 17: The Error TLV
Different types of errors can occur while processing Converter Different types of errors can occur while processing Convert
protocol messages. Each error is identified by a code represented as messages. Each error is identified by a code represented as an
an unsigned integer. Four classes of errors are defined: unsigned integer. Four classes of errors are defined:
o Message validation and processing errors (0<= error code <= 31): o Message validation and processing errors (0-31 range): returned
returned upon reception of an an invalid message (including valid upon reception of an an invalid message (including valid messages
messages but with invalid or unknown TLVs). but with invalid or unknown TLVs).
o Client-side errors (32<= error code <= 63): the Client sent a o Client-side errors (32-63 range): the Client sent a request that
request that could not be accepted by the Converter (e.g., could not be accepted by the Converter (e.g., unsupported
unsupported operation). operation).
o Converter-side errors (64<= error code <96) : problems encountered o Converter-side errors (64-95 range) : problems encountered on the
on the Converter (e.g., lack of ressources) which prevent it from Converter (e.g., lack of resources) which prevent it from
fulfilling the Client's request. fulfilling the Client's request.
o Errors caused by destination server (96<= error code <= 127) : the o Errors caused by destination server (96-127 range) : the final
final destination could not be reached or it replied with a reset destination could not be reached or it replied with a reset
message. message.
The following errors are defined in this document: The following error codes are defined in this document:
o Unsupported Version (0): The version number indicated in the fixed o Unsupported Version (0): The version number indicated in the fixed
header of a message received from a peer is not supported. This header of a message received from a peer is not supported.
error code MUST be generated by a Converter when it receives a
request having a version number that it does not support. The This error code MUST be generated by a Converter when it receives
value field MUST be set to the version supported by the Converter. a request having a version number that it does not support.
When multiple versions are supported by the converter, it includes
the list of supported version in the value field; each version is The value field MUST be set to the version supported by the
encoded in 8 bits. Upon receipt of this error code, the client Converter. When multiple versions are supported by the Converter,
checks whether it supports one of the versions returned by the it includes the list of supported version in the value field; each
Converter. The highest common supported version MUST be used by version is encoded in 8 bits.
the client in subsequent exchanges with the Converter.
Upon receipt of this error code, the client checks whether it
supports one of the versions returned by the Converter. The
highest common supported version MUST be used by the client in
subsequent exchanges with the Converter.
o Malformed Message (1): This error code is sent to indicate that a o Malformed Message (1): This error code is sent to indicate that a
message can not be successfully parsed. To ease troubleshooting, message can not be successfully parsed.
the value field MUST echo the received message. The Converter and
the Client MUST send a RST containing this error upon reception of To ease troubleshooting, the value field MUST echo the received
a malformed message. message. The Converter and the Client MUST send a RST containing
this error upon reception of a malformed message.
o Unsupported Message (2): This error code is sent to indicate that o Unsupported Message (2): This error code is sent to indicate that
a message type is not supported by the converter. To ease a message type is not supported by the Converter.
troubleshooting, the value field MUST echo the received message.
The Converter and the Client MUST send a RST containing this error To ease troubleshooting, the value field MUST echo the received
upon reception of an unsupported message. message. The Converter and the Client MUST send a RST containing
this error upon reception of an unsupported message.
o Not Authorized (32): This error code indicates that the Converter o Not Authorized (32): This error code indicates that the Converter
refused to create a connection because of a lack of authorization refused to create a connection because of a lack of authorization
(e.g., administratively prohibited, authorization failure, etc.). (e.g., administratively prohibited, authorization failure, etc.).
The Value field is set to zero. This error code MUST be sent by The Value field MUST be set to zero.
the Converter when a request cannot be successfully processed
because the authorization failed.
o Unsupported TCP Option (33). A TCP Option that the Client This error code MUST be sent by the Converter when a request
requested to advertise to the final Server is not supported by the cannot be successfully processed because the authorization failed.
Transport Converter. The Value field is set to the type of the
unsupported TCP Option. If several unsupported TCP Options were o Unsupported TCP Option (33): A TCP option that the Client
specified in the Connect TLV, only one of them is returned in the requested to advertise to the final Server cannot be safely used
Value. jointly with the conversion service.
The Value field is set to the type of the unsupported TCP option.
If several unsupported TCP options were specified in the Connect
TLV, only one of them is returned in the Value.
o Resource Exceeded (64): This error indicates that the Transport o Resource Exceeded (64): This error indicates that the Transport
Converter does not have enough resources to perform the request. Converter does not have enough resources to perform the request.
This error MUST be sent by the Converter when it does not have This error MUST be sent by the Converter when it does not have
sufficient resources to handle a new connection. sufficient resources to handle a new connection.
o Network Failure (65): This error indicates that the converter is o Network Failure (65): This error indicates that the Converter is
experiencing a network failure to relay the request. The experiencing a network failure to relay the request.
converter MUST send this error code when it experiences forwarding
issues to relay a connection. The Converter MUST send this error code when it experiences
forwarding issues to relay a connection.
o Connection Reset (96): This error indicates that the final o Connection Reset (96): This error indicates that the final
destination responded with a RST packet. The Value field is set destination responded with a RST packet. The Value field MUST be
to zero. set to zero.
o Destination Unreachable (97): This error indicates that an ICMP o Destination Unreachable (97): This error indicates that an ICMP
destination unreachable, port unreachable, or network unreachable destination unreachable, port unreachable, or network unreachable
was received by the Converter. The Value field contains the Code was received by the Converter. The Value field MUST echo the Code
field of the received ICMP message. This error message MUST be field of the received ICMP message.
sent by the Converter when it receives an error message that is
bound to a message it relayed previously.
Table 2 summarizes the different error codes. This error message MUST be sent by the Converter when it receives
an error message that is bound to a message it relayed previously.
+-------+------+-------------------------+ Figure 18 summarizes the different error codes.
| Error | Hex | Description |
+-------+------+-------------------------+
| 0 | 0x00 | Unsupported version |
| | | |
| 1 | 0x01 | Malformed Message |
| | | |
| 2 | 0x02 | Unsupported Message |
| | | |
| 32 | 0x20 | Not Authorized |
| | | |
| 33 | 0x21 | Unsupported TCP Option |
| | | |
| 64 | 0x40 | Resource Exceeded |
| | | |
| 65 | 0x41 | Network Failure |
| | | |
| 96 | 0x60 | Connection Reset |
| | | |
| 97 | 0x61 | Destination Unreachable |
+-------+------+-------------------------+
Table 2: The different error codes +-------+------+-----------------------------------------------+
| Error | Hex | Description |
+-------+------+-----------------------------------------------+
| 0 | 0x00 | Unsupported Version |
| 1 | 0x01 | Malformed Message |
| 2 | 0x02 | Unsupported Message |
| 32 | 0x20 | Not Authorized |
| 33 | 0x21 | Unsupported TCP Option |
| 64 | 0x40 | Resource Exceeded |
| 65 | 0x41 | Network Failure |
| 96 | 0x60 | Connection Reset |
| 97 | 0x61 | Destination Unreachable |
+-------+------+-----------------------------------------------+
4.3.4. The Bootstrap TLV Figure 18: Convert Error Values
The Bootstrap TLV is sent by a Client to request the TCP Extensions 5. Compatibility of Specific TCP Options with the Conversion Service
that are supported by a Transport Converter. It is typically sent on
the first connection that a Client establishes with a Transport
Converter to learn its capabilities. The Transport Converter replies
with the Supported TCP Options TLV described in Section 4.3.5.
1 2 3 In this section, we discuss how several standard track TCP options
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 can be supported through the Converter. The non-standard track
+---------------+---------------+-------------------------------+ options and the experimental options will be discussed in other
| Type | Length | Zero | documents.
+---------------+---------------+-------------------------------+
Figure 15: The Bootstrap TLV 5.1. Base TCP Options
4.3.5. Supported TCP Options TLV Three TCP options were initially defined in [RFC0793] : End-of-Option
List (Kind=0), No-Operation (Kind=1) and Maximum Segment Size
(Kind=2). The first two options are mainly used to pad the TCP
extended header. There is no reason for a client to request a
Converter to specifically send these options towards the final
destination.
The Supported TCP Options TLV is used by a Converter to announce the The Maximum Segment Size option (Kind=2) is used by a host to
TCP options that it supports. Each supported TCP Option is encoded indicate the largest segment that it can receive over each
with its TCP option Kind listed in the TCP Parameters registry connection. This value is function of the stack that terminates the
maintained by IANA. TCP option Kinds 0, 1, and 2 defined in TCP connection. There is no reason for a Client to request a
[RFC0793] are supported by all TCP implementations and thus cannot Converter to advertise a specific MSS value to a remote server.
appear in this list. The list of supported TCP Options is padded
with 0 to end on a 32 bits boundary.
1 2 3 A Converter MUST ignore options with Kind=0, 1 or 2 if they appear in
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 a Connect TLV. It MUST NOT announce them in a Bootstrap TLV.
+---------------+---------------+-------------------------------+
| Type | Length | Reserved |
+---------------+---------------+-------------------------------+
| Kind #1 | Kind #2 | ... |
+---------------+---------------+-------------------------------+
/ ... /
/ /
+---------------------------------------------------------------+
Figure 16: The Supported TCP Options TLV 5.2. Window Scale (WS)
5. Interactions with middleboxes The Window Scale option (Kind=3) is defined in [RFC7323]. As for the
MSS option, the window scale factor that is used for a connection
strongly depends on the TCP stack that handles the connection. When
a Converter opens a TCP connection towards a remote server on behalf
of a Client, it SHOULD use a WS option with a scaling factor that
corresponds to the configuration of its stack. A local configuration
MAY allow for WS option in the proxied message to be function of the
scaling factor of the incoming connection.
The Converter protocol was designed to be used in networks that do There is no benefit from a deployment viewpoint in enabling a Client
of a Converter to specifically request the utilisation of the WS
option (Kind=3) with a specific scaling factor towards a remote
Server. For this reason, a Converter MUST ignore option Kind=3 if it
appears in a Connect TLV. It MUST NOT announce it in a Bootstrap
TLV.
5.3. Selective Acknowledgements
Two distinct TCP options were defined to support selective
acknowledgements in [RFC2018]. This first one, SACK Permitted
(Kind=4), is used to negotiate the utilisation of selective
acknowledgements during the three-way handshake. The second one,
SACK (Kind=5), carries the selective acknowledgements inside regular
segments.
The SACK Permitted option (Kind=4) MAY be advertised by a Transport
Converter in the Bootstrap TLV. In this case, Clients connected to
this Transport Converter MAY include the SACK Permitted option in the
Connect TLV.
The SACK option (Kind=5) cannot be used during the three-way
handshake. For this reason, a Transport Converter MUST ignore option
Kind=5 with if it appears in a Connect TLV. It MUST NOT announce it
in a Bootstrap TLV.
5.4. Timestamp
The Timestamp option was initially defined in [RFC1323] which has
been replaced by [RFC7323]. It can be used during the three-way
handshake to negotiate the utilisation of the timestamps during the
TCP connection. It is notably used to improve round-trip-time
estimations and to provide protection against wrapped sequence
numbers (PAWS). As for the WS option, the timestamps are a property
of a connection and there is limited benefit in enabling a client to
request a Converter to use the timestamp option when establishing a
connection to a remote server. Furthermore, the timestamps that are
used by TCP stacks are specific to each stack and there is no benefit
in enabling a client to specify the timestamp value that a Converter
could use to establish a connection to a remote server.
A Transport Converter MAY advertise the Timestamp option (Kind=8) in
the Bootstrap TLV. The clients connected to this Converter MAY
include the Timestamp option in the Connect TLV but without any
timestamp.
5.5. Multipath TCP
The Multipath TCP options are defined in [RFC6824]. [RFC6824]
defines one variable length TCP option (Kind=30) that includes a
subtype field to support several Multipath TCP options. There are
several operational use cases where clients would like to use
Multipath TCP through a Converter [IETFJ16]. However, none of these
use cases require the Client to specify the content of the Multipath
TCP option that the Converter should send to a remote server.
A Transport Converter which supports Multipath TCP conversion service
MUST advertise the Multipath TCP option (Kind=30) in the Bootstrap
TLV. Clients serviced by this Converter may include the Multipath
TCP option in the Connect TLV but without any content.
5.6. TCP Fast Open
The TCP Fast Open cookie option (Kind=34) is defined in [RFC7413].
There are two different usages of this option that need to be
supported by Transport Converters. The first utilisation of the Fast
Open cookie is to request a cookie from the server. In this case,
the option is sent with an empty cookie by the client and the server
returns the cookie. The second utilisation of the Fast Open cookie
is to send a cookie to the server. In this case, the option contains
a cookie.
A Transport Converter MAY advertise the TCP Fast Open cookie option
(Kind=34) in the Bootstrap TLV. If a Transport Converter has
advertised the support for TCP Fast Open in its Bootstrap TLV, it
needs to be able to process two types of Connect TLV. If such a
Transport Converter receives a Connect TLV with the TCP Fast Open
cookie option that does not contain a cookie, it MUST add an empty
TCP Fast Open cookie option in the SYN sent to the remote server. If
such a Transport Converter receives a Connect TLV with the TCP Fast
Open cookie option that contains a cookie, it MUST copy the TCP Fast
Open cookie option in the SYN sent to the remote server.
5.7. TCP User Timeout
The TCP User Timeout option is defined in [RFC5482]. The associated
TCP option (Kind=28) does not appear to be widely deployed.
Editor's Note: Feedback requested for the utilisation of this option
by deployed TCP stacks.
5.8. TCP-AO
TCP-AO [RFC5925] provides a technique to authenticate all the packets
exchanged over a TCP connection. Given the nature of this extension,
it is unlikely that the applications that require their packets to be
authenticated end-to-end would want their connections to pass through
a converter. For this reason, we do not recommend the support of the
TCP-AO option by Transport Converters. The only use cases where is
makes sense to combine TCP-AO and the solution in this document are
those where the TCP-AO-NAT extension [RFC6978] is in use.
A Converter MUST NOT advertise the TCP-AO option (Kind=29) in the
Bootstrap TLV. If a Converter receives a Connect TLV that contains
the TCP-AO option, it MUST reject the establishment of the connection
with error code set to "Unsupported TCP Option", except if the TCP-
AO-NAT option is used.
5.9. TCP Experimental Options
The TCP Experimental options are defined in [RFC4727]. Given the
variety of semantics for these options and their experimental nature,
it is impossible to discuss them in details in this document.
6. Interactions with Middleboxes
The Converter Protocol was designed to be used in networks that do
not contain middleboxes that interfere with TCP. We describe in this not contain middleboxes that interfere with TCP. We describe in this
section how a Client can detect middlebox interference and stop using section how a Client can detect middlebox interference and stop using
the Transport Converter affected by this interference. the Transport Converter affected by this interference.
Internet measurements [IMC11] have shown that middleboxes can affect Internet measurements [IMC11] have shown that middleboxes can affect
the deployment of TCP extensions. In this section, we only discuss the deployment of TCP extensions. In this section, we only discuss
the middleboxes that modify SYN and SYN+ACK packets since the the middleboxes that modify SYN and SYN+ACK packets since the
Converter protocol places its messages in such packets. Converter Protocol places its messages in such packets.
Let us first consider a middlebox that removes the TFO Option from Let us first consider a middlebox that removes the TFO Option from
the SYN packet. This interference will be detected by the Client the SYN packet. This interference will be detected by the Client
during the bootstrap procedure shown in Figure 5. A Client should during the bootstrap procedure discussed in Section 4.2.3. A Client
not use a Transport Converter that does not reply with the TFO option should not use a Transport Converter that does not reply with the TFO
during the Bootstrap. option during the Bootstrap.
Consider a middlebox that removes the SYN payload after the bootstrap Consider a middlebox that removes the SYN payload after the bootstrap
procedure. The Client can detect this problem by looking at the procedure. The Client can detect this problem by looking at the
acknowledgement number field of the SYN+ACK returned by the Transport acknowledgement number field of the SYN+ACK returned by the Transport
Converter. The Client should stop to use this Transport Converter Converter. The Client should stop to use this Transport Converter
given the middlebox interference. given the middlebox interference.
As explained in [RFC7413], some carrier-grade NATs can affect the As explained in [RFC7413], some carrier-grade NATs can affect the
operation of TFO if they assign different IP addresses to the same operation of TFO if they assign different IP addresses to the same
end host. Such carrier-grade NATs could affect the operation of the end host. Such carrier-grade NATs could affect the operation of the
TFO Option used by the Converter protocol. See also the discussion TFO Option used by the Converter Protocol. See also the discussion
in section 7.1 of [RFC7413]. in Section 7.1 of [RFC7413].
6. Security Considerations 7. Security Considerations
6.1. Privacy & Ingress Filtering 7.1. Privacy & Ingress Filtering
The Converter may have access to privacy-related information (e.g., The Converter may have access to privacy-related information (e.g.,
subscriber credentials). The Converter MUST NOT leak such sensitive subscriber credentials). The Converter MUST NOT leak such sensitive
information outside a local domain. information outside a local domain.
Given its function and its location in the network, a Transport Given its function and its location in the network, a Transport
Converter has access to the payload of all the packets that it Converter has access to the payload of all the packets that it
processes. As such, it must be protected as a core IP router. processes. As such, it MUST be protected as a core IP router (e.g.,
[RFC1812]).
Furthermore, ingress filtering policies MUST be enforced at the Furthermore, ingress filtering policies MUST be enforced at the
network boundaries [RFC2827]. network boundaries [RFC2827].
This document assumes that all network attachements are managed by This document assumes that all network attachments are managed by the
the same administrative entity. Therefore, enforcing anti-spoofing same administrative entity. Therefore, enforcing anti-spoofing
filters at these network ensures that hosts are not sending traffic filters at these network ensures that hosts are not sending traffic
with spoofed source IP addresses. with spoofed source IP addresses.
6.2. Authorization 7.2. Authorization
The Converter protocol is intended to be used in managed networks The Converter Protocol is intended to be used in managed networks
where end hosts can be identified by their IP address. Thanks to the where end hosts can be identified by their IP address. Thanks to the
Bootstrap procedure (Figure 5), the Transport Converter can verify Bootstrap procedure, the Transport Converter can verify that the
that the Client correctly receives packets sent by the Converter. Client correctly receives packets sent by the Converter. Stronger
Stronger authentication schemes should be defined to use the authentication schemes MUST be defined to use the Converter Protocol
Converter protocol in more open network environments. in more open network environments; such schemes are out of scope of
this document.
See below for authorization considerations that are specific for See below for authorization considerations that are specific for
Multipath TCP. Multipath TCP.
6.3. Denial of Service 7.3. Denial of Service
Another possible risk is the amplification attacks since a Transport Another possible risk is the amplification attacks since a Transport
Converter sends a SYN towards a remote Server upon reception of a SYN Converter sends a SYN towards a remote Server upon reception of a SYN
from a Client. This could lead to amplification attacks if the SYN from a Client. This could lead to amplification attacks if the SYN
sent by the Transport Converter were larger than the SYN received sent by the Transport Converter were larger than the SYN received
from the Client or if the Transport Converter retransmits the SYN. from the Client or if the Transport Converter retransmits the SYN.
To mitigate such attacks, the Transport Converter SHOULD rate limit To mitigate such attacks, the Transport Converter SHOULD rate limit
the number of pending requests for a given Client. It SHOULD also the number of pending requests for a given Client. It SHOULD also
avoid sending to remote Servers SYNs that are significantly longer avoid sending to remote Servers SYNs that are significantly longer
than the SYN received from the Client. In practice, Transport than the SYN received from the Client. In practice, Transport
Converters SHOULD NOT advertise to a Server TCP Options that were not Converters SHOULD NOT advertise to a Server TCP options that were not
specified by the Client in the received SYN. Finally, the Transport specified by the Client in the received SYN. Finally, the Transport
Converter SHOULD only retransmit a SYN to a Server after having Converter SHOULD only retransmit a SYN to a Server after having
received a retransmitted SYN from the corresponding Client. received a retransmitted SYN from the corresponding Client.
Upon reception of a SYN that contains a valid TFO Cookie and a Upon reception of a SYN that contains a valid TFO cookie and a
Connect TLV, the Transport Converter attempts to establish a TCP Connect TLV, the Transport Converter attempts to establish a TCP
connection to a remote Server. There is a risk of denial of service connection to a remote Server. There is a risk of denial of service
attack if a Client requests too many connections in a short period of attack if a Client requests too many connections in a short period of
time. Implementations SHOULD limit the number of pending connections time. Implementations SHOULD limit the number of pending connections
from a given Client. Means to protect against SYN flooding attacks from a given Client. Means to protect against SYN flooding attacks
MUST also be enabled [RFC4987]. MUST also be enabled [RFC4987].
6.4. Traffic Theft 7.4. Traffic Theft
Traffic theft is a risk if an illegitimate Converter is inserted in Traffic theft is a risk if an illegitimate Converter is inserted in
the path. Indeed, inserting an illegitimate Converter in the the path. Indeed, inserting an illegitimate Converter in the
forwarding path allows traffic interception and can therefore provide forwarding path allows traffic interception and can therefore provide
access to sensitive data issued by or destined to a host. Converter access to sensitive data issued by or destined to a host. Converter
discovery and configuration are out of scope of this document. discovery and configuration are out of scope of this document.
6.5. Multipath TCP-specific Considerations 7.5. Multipath TCP-specific Considerations
Multipath TCP-related security threats are discussed in [RFC6181] and Multipath TCP-related security threats are discussed in [RFC6181] and
[RFC6824]. [RFC6824].
The operator that manages the various network attachments (including The operator that manages the various network attachments (including
the Converters) can enforce authentication and authorization policies the Converters) can enforce authentication and authorization policies
using appropriate mechanisms. For example, a non-exhaustive list of using appropriate mechanisms. For example, a non-exhaustive list of
methods to achieve authorization is provided hereafter: methods to achieve authorization is provided hereafter:
o The network provider may enforce a policy based on the o The network provider may enforce a policy based on the
skipping to change at page 27, line 5 skipping to change at page 27, line 17
received from a given source IP address are authorized or not received from a given source IP address are authorized or not
[I-D.boucadair-mptcp-radius]. [I-D.boucadair-mptcp-radius].
A first safeguard against the misuse of Converter resources by A first safeguard against the misuse of Converter resources by
illegitimate users (e.g., users with access networks that are not illegitimate users (e.g., users with access networks that are not
managed by the same provider that operates the Converter) is the managed by the same provider that operates the Converter) is the
Converter to reject Multipath TCP connections received on its Converter to reject Multipath TCP connections received on its
Internet-facing interfaces. Only Multipath PTCP connections received Internet-facing interfaces. Only Multipath PTCP connections received
on the customer-facing interfaces of a Converter will be accepted. on the customer-facing interfaces of a Converter will be accepted.
7. IANA Considerations 8. IANA Considerations
This document requests the allocation of a reserved service name and 8.1. Convert Service Port Number
port number for the converter protocol at https://www.iana.org/
assignments/service-names-port-numbers/
service-names-port-numbers.xhtml.
This documents specifies version 1 of the Converter protocol. Five IANA is requested to assign a TCP port number (TBA) for the Converter
types of Converter messages are defined: Protocol from the "Service Name and Transport Protocol Port Number
Registry" available at https://www.iana.org/assignments/service-
names-port-numbers/service-names-port-numbers.xhtml.
o 1: Bootstrap TLV 8.2. The Converter Protocol (Convert) Parameters
o 10: Connect TLV IANA is requested to create a new "The Converter Protocol (Convert)
Parameters" registry.
o 20: Extended TCP Header TLV The following subsections detail new registries within "The Converter
Protocol (Convert) Parameters" registry.
o 21: Supported TCP Options TLV 8.2.1. Convert Versions
o 30: Error TLV IANA is requested to create the "Convert versions" sub-registry. New
values are assigned via Standards Action.
Furthermore, it also defines the following error codes: The initial values to be assigned at the creation of the registry are
as follows:
+-------+------+-------------------------+ +---------+--------------------------------------+-------------+
| Error | Hex | Description | | Version | Description | Reference |
+-------+------+-------------------------+ +---------+--------------------------------------+-------------+
| 0 | 0x00 | Unsupported version | | 0 | Reserved by this document | [This-RFC] |
| | | | | 1 | Assigned by this document | [This-RFC] |
| 1 | 0x01 | Malformed Message | +---------+--------------------------------------+-------------+
| | | |
| 2 | 0x02 | Unsupported Message |
| | | |
| 32 | 0x20 | Not Authorized |
| | | |
| 33 | 0x21 | Unsupported TCP Option |
| | | |
| 64 | 0x40 | Resource Exceeded |
| | | |
| 65 | 0x41 | Network Failure |
| | | |
| 96 | 0x60 | Connection Reset |
| | | |
| 97 | 0x61 | Destination Unreachable |
+-------+------+-------------------------+
Table 3: The different error codes 8.2.2. Convert TLVs
8. Acknowledgements IANA is requested to create the "Convert TLVs" sub-registry. The
procedure for assigning values from this registry is as follows:
o The values in the range 1-127 can be assigned via Standards
Action.
o The values in the range 128-191 can be assigned via Specification
Required.
o The values in the range 192-255 can be assigned for Private Use.
The initial values to be assigned at the creation of the registry are
as follows:
+---------+--------------------------------------+-------------+
| Code | Name | Reference |
+---------+--------------------------------------+-------------+
| 0 | Reserved | [This-RFC] |
| 1 | Bootstrap TLV | [This-RFC] |
| 10 | Connect TLV | [This-RFC] |
| 20 | Extended TCP Header TLV | [This-RFC] |
| 22 | Supported TCP Extension Services TLV | [This-RFC] |
| 30 | Error TLV | [This-RFC] |
+---------+--------------------------------------+-------------+
8.2.3. Convert Error Messages
IANA is requested to create the "Convert Errors" sub-registry. Codes
in this registry are assigned as a function of the error type. Four
types are defined; the following ranges are reserved for each of
these types:
o Message validation and processing errors: 0-31
o Client-side errors: 32-63
o Converter-side errors: 64-95
o Errors caused by destination server: 96-127
The procedure for assigning values from this sub-registry is as
follows:
o 0-191: Values in this range are assigned via Standards Action.
o 192-255: Values in this range are assigned via Specification
Required.
The initial values to be assigned at the creation of the registry are
as follows:
+-------+------+-----------------------------------+-----------+
| Error | Hex | Description | Reference |
+-------+------+-----------------------------------+-----------+
| 0 | 0x00 | Unsupported Version | [This-RFC]|
| 1 | 0x01 | Malformed Message | [This-RFC]|
| 2 | 0x02 | Unsupported Message | [This-RFC]|
| 32 | 0x20 | Not Authorized | [This-RFC]|
| 33 | 0x21 | Unsupported TCP Option | [This-RFC]|
| 64 | 0x40 | Resource Exceeded | [This-RFC]|
| 65 | 0x41 | Network Failure | [This-RFC]|
| 96 | 0x60 | Connection Reset | [This-RFC]|
| 97 | 0x61 | Destination Unreachable | [This-RFC]|
+-------+------+-----------------------------------+-----------+
Figure 19: The Convert Error Codes
9. Acknowledgements
Although they could disagree with the contents of the document, we Although they could disagree with the contents of the document, we
would like to thank Joe Touch and Juliusz Chroboczek whose comments would like to thank Joe Touch and Juliusz Chroboczek whose comments
on the MPTCP mailing list have forced us to reconsider the design of on the MPTCP mailing list have forced us to reconsider the design of
the solution several times. the solution several times.
We would like to thank Raphael Bauduin and Stefano Secci for their We would like to thank Raphael Bauduin, Stefano Secci, and Benjamin
help in preparing this draft. Sri Gundavelli and Nandini Ganesh Hesmans for their help in preparing this document. Sri Gundavelli
provided valuable feedback about the handling of TFO and the error and Nandini Ganesh provided valuable feedback about the handling of
codes. Thanks to them. TFO and the error codes. Thanks to them.
This document builds upon earlier documents that proposed various This document builds upon earlier documents that proposed various
forms of Multipath TCP proxies [I-D.boucadair-mptcp-plain-mode], forms of Multipath TCP proxies [I-D.boucadair-mptcp-plain-mode],
[I-D.peirens-mptcp-transparent] and [HotMiddlebox13b]. [I-D.peirens-mptcp-transparent] and [HotMiddlebox13b].
From [I-D.boucadair-mptcp-plain-mode]: From [I-D.boucadair-mptcp-plain-mode]:
Many thanks to Chi Dung Phung, Mingui Zhang, Rao Shoaib, Yoshifumi Many thanks to Chi Dung Phung, Mingui Zhang, Rao Shoaib, Yoshifumi
Nishida, and Christoph Paasch for their valuable comments. Nishida, and Christoph Paasch for their valuable comments.
skipping to change at page 28, line 38 skipping to change at page 30, line 13
Aires). Aires).
Special thanks to Pierrick Seite, Yannick Le Goff, Fred Klamm, and Special thanks to Pierrick Seite, Yannick Le Goff, Fred Klamm, and
Xavier Grall for their inputs. Xavier Grall for their inputs.
Thanks also to Olaf Schleusing, Martin Gysi, Thomas Zasowski, Andreas Thanks also to Olaf Schleusing, Martin Gysi, Thomas Zasowski, Andreas
Burkhard, Silka Simmen, Sandro Berger, Michael Melloul, Jean-Yves Burkhard, Silka Simmen, Sandro Berger, Michael Melloul, Jean-Yves
Flahaut, Adrien Desportes, Gregory Detal, Benjamin David, Arun Flahaut, Adrien Desportes, Gregory Detal, Benjamin David, Arun
Srinivasan, and Raghavendra Mallya for the discussion. Srinivasan, and Raghavendra Mallya for the discussion.
8.1. Contributors 9.1. Contributors
As noted above, this document builds on two previous documents. As noted above, this document builds on two previous documents.
The authors of [I-D.boucadair-mptcp-plain-mode] were: - Mohamed The authors of [I-D.boucadair-mptcp-plain-mode] were: - Mohamed
Boucadair - Christian Jacquenet - Olivier Bonaventure - Denis Boucadair - Christian Jacquenet - Olivier Bonaventure - Denis
Behaghel - Stefano Secci - Wim Henderickx - Robert Skog - Suresh Behaghel - Stefano Secci - Wim Henderickx - Robert Skog - Suresh
Vinapamula - SungHoon Seo - Wouter Cloetens - Ullrich Meyer - Luis M. Vinapamula - SungHoon Seo - Wouter Cloetens - Ullrich Meyer - Luis M.
Contreras - Bart Peirens Contreras - Bart Peirens
The authors of [I-D.peirens-mptcp-transparent] were: - Bart Peirens - The authors of [I-D.peirens-mptcp-transparent] were: - Bart Peirens -
Gregory Detal - Sebastien Barre - Olivier Bonaventure Gregory Detal - Sebastien Barre - Olivier Bonaventure
9. References 10. Change Log
9.1. Normative References This section to be removed before publication.
o 00 : initial version, designed to support Multipath TCP and TFO
only
o 00 to -01 : added section Section 5 describing the support of
different standard tracks TCP options by Transport Converters,
clarification of the IANA section, moved the SOCKS comparison to
the appendix and various minor modifications
11. References
11.1. Normative References
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, [RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981, RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>. <https://www.rfc-editor.org/info/rfc793>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ Requirement Levels", BCP 14, RFC 2119,
RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, Architecture", RFC 4291, DOI 10.17487/RFC4291, February
February 2006, <https://www.rfc-editor.org/info/rfc4291>. 2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4,
ICMPv6, UDP, and TCP Headers", RFC 4727,
DOI 10.17487/RFC4727, November 2006,
<https://www.rfc-editor.org/info/rfc4727>.
[RFC4987] Eddy, W., "TCP SYN Flooding Attacks and Common [RFC4987] Eddy, W., "TCP SYN Flooding Attacks and Common
Mitigations", RFC 4987, DOI 10.17487/RFC4987, August 2007, Mitigations", RFC 4987, DOI 10.17487/RFC4987, August 2007,
<https://www.rfc-editor.org/info/rfc4987>. <https://www.rfc-editor.org/info/rfc4987>.
[RFC5482] Eggert, L. and F. Gont, "TCP User Timeout Option",
RFC 5482, DOI 10.17487/RFC5482, March 2009,
<https://www.rfc-editor.org/info/rfc5482>.
[RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP
Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
June 2010, <https://www.rfc-editor.org/info/rfc5925>.
[RFC6824] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure, [RFC6824] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
"TCP Extensions for Multipath Operation with Multiple "TCP Extensions for Multipath Operation with Multiple
Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013, Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013,
<https://www.rfc-editor.org/info/rfc6824>. <https://www.rfc-editor.org/info/rfc6824>.
[RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP [RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP
Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014, Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014,
<https://www.rfc-editor.org/info/rfc7413>. <https://www.rfc-editor.org/info/rfc7413>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
9.2. Informative References 11.2. Informative References
[ANRW17] Trammell, B., Kuhlewind, M., De Vaere, P., Learmonth, I., [ANRW17] Trammell, B., Kuhlewind, M., De Vaere, P., Learmonth, I.,
and G. Fairhurst, "Tracking transport-layer evolution with and G. Fairhurst, "Tracking transport-layer evolution with
PATHspider", Applied Networking Research Workshop 2017 PATHspider", Applied Networking Research Workshop 2017
(ANRW17) , July 2017. (ANRW17) , July 2017.
[Fukuda2011] [Fukuda2011]
Fukuda, K., "An Analysis of Longitudinal TCP Passive Fukuda, K., "An Analysis of Longitudinal TCP Passive
Measurements (Short Paper)", Traffic Monitoring and Measurements (Short Paper)", Traffic Monitoring and
Analysis. TMA 2011. Lecture Notes in Computer Science, vol Analysis. TMA 2011. Lecture Notes in Computer Science, vol
6613. , 2011. 6613. , 2011.
[HotMiddlebox13b] [HotMiddlebox13b]
Detal, G., Paasch, C., and O. Bonaventure, "Multipath in Detal, G., Paasch, C., and O. Bonaventure, "Multipath in
the Middle(Box)", HotMiddlebox'13 , December 2013, <http:/ the Middle(Box)", HotMiddlebox'13 , December 2013,
/inl.info.ucl.ac.be/publications/multipath-middlebox>. <http://inl.info.ucl.ac.be/publications/
multipath-middlebox>.
[I-D.arkko-arch-low-latency] [I-D.arkko-arch-low-latency]
Arkko, J. and J. Tantsura, "Low Latency Applications and Arkko, J. and J. Tantsura, "Low Latency Applications and
the Internet Architecture", the Internet Architecture", draft-arkko-arch-low-
draft-arkko-arch-low-latency-02 (work in progress), latency-02 (work in progress), October 2017.
October 2017.
[I-D.boucadair-mptcp-plain-mode] [I-D.boucadair-mptcp-plain-mode]
Boucadair, M., Jacquenet, C., Bonaventure, O., Behaghel, Boucadair, M., Jacquenet, C., Bonaventure, O., Behaghel,
D., stefano.secci@lip6.fr, s., Henderickx, W., Skog, R., D., stefano.secci@lip6.fr, s., Henderickx, W., Skog, R.,
Vinapamula, S., Seo, S., Cloetens, W., Meyer, U., Vinapamula, S., Seo, S., Cloetens, W., Meyer, U.,
Contreras, L., and B. Peirens, "Extensions for Network- Contreras, L., and B. Peirens, "Extensions for Network-
Assisted MPTCP Deployment Models", Assisted MPTCP Deployment Models", draft-boucadair-mptcp-
draft-boucadair-mptcp-plain-mode-10 (work in progress), plain-mode-10 (work in progress), March 2017.
March 2017.
[I-D.boucadair-mptcp-radius] [I-D.boucadair-mptcp-radius]
Boucadair, M. and C. Jacquenet, "RADIUS Extensions for Boucadair, M. and C. Jacquenet, "RADIUS Extensions for
Network-Assisted Multipath TCP (MPTCP)", Network-Assisted Multipath TCP (MPTCP)", draft-boucadair-
draft-boucadair-mptcp-radius-05 (work in progress), mptcp-radius-05 (work in progress), October 2017.
October 2017.
[I-D.ietf-mptcp-rfc6824bis] [I-D.ietf-mptcp-rfc6824bis]
Ford, A., Raiciu, C., Handley, M., Bonaventure, O., and C. Ford, A., Raiciu, C., Handley, M., Bonaventure, O., and C.
Paasch, "TCP Extensions for Multipath Operation with Paasch, "TCP Extensions for Multipath Operation with
Multiple Addresses", draft-ietf-mptcp-rfc6824bis-09 (work Multiple Addresses", draft-ietf-mptcp-rfc6824bis-10 (work
in progress), July 2017. in progress), March 2018.
[I-D.ietf-tcpinc-tcpcrypt] [I-D.ietf-tcpinc-tcpcrypt]
Bittau, A., Giffin, D., Handley, M., Mazieres, D., Slack, Bittau, A., Giffin, D., Handley, M., Mazieres, D., Slack,
Q., and E. Smith, "Cryptographic protection of TCP Streams Q., and E. Smith, "Cryptographic protection of TCP Streams
(tcpcrypt)", draft-ietf-tcpinc-tcpcrypt-11 (work in (tcpcrypt)", draft-ietf-tcpinc-tcpcrypt-11 (work in
progress), November 2017. progress), November 2017.
[I-D.olteanu-intarea-socks-6] [I-D.olteanu-intarea-socks-6]
Olteanu, V. and D. Niculescu, "SOCKS Protocol Version 6", Olteanu, V. and D. Niculescu, "SOCKS Protocol Version 6",
draft-olteanu-intarea-socks-6-01 (work in progress), draft-olteanu-intarea-socks-6-01 (work in progress),
October 2017. October 2017.
[I-D.peirens-mptcp-transparent] [I-D.peirens-mptcp-transparent]
Peirens, B., Detal, G., Barre, S., and O. Bonaventure, Peirens, B., Detal, G., Barre, S., and O. Bonaventure,
"Link bonding with transparent Multipath TCP", "Link bonding with transparent Multipath TCP", draft-
draft-peirens-mptcp-transparent-00 (work in progress), peirens-mptcp-transparent-00 (work in progress), July
July 2016. 2016.
[IETFJ16] Bonaventure, O. and S. Seo, "Multipath TCP Deployment", [IETFJ16] Bonaventure, O. and S. Seo, "Multipath TCP Deployment",
IETF Journal, Fall 2016 , n.d.. IETF Journal, Fall 2016 , n.d..
[IMC11] Honda, K., Nishida, Y., Raiciu, C., Greenhalgh, A., [IMC11] Honda, K., Nishida, Y., Raiciu, C., Greenhalgh, A.,
Handley, M., and T. Hideyuki, "Is it still possible to Handley, M., and T. Hideyuki, "Is it still possible to
extend TCP ?", Proceedings of the 2011 ACM SIGCOMM extend TCP ?", Proceedings of the 2011 ACM SIGCOMM
conference on Internet measurement conference , 2011. conference on Internet measurement conference , 2011.
[RFC1323] Jacobson, V., Braden, R., and D. Borman, "TCP Extensions
for High Performance", RFC 1323, DOI 10.17487/RFC1323, May
1992, <https://www.rfc-editor.org/info/rfc1323>.
[RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers",
RFC 1812, DOI 10.17487/RFC1812, June 1995,
<https://www.rfc-editor.org/info/rfc1812>.
[RFC1919] Chatel, M., "Classical versus Transparent IP Proxies", [RFC1919] Chatel, M., "Classical versus Transparent IP Proxies",
RFC 1919, DOI 10.17487/RFC1919, March 1996, RFC 1919, DOI 10.17487/RFC1919, March 1996,
<https://www.rfc-editor.org/info/rfc1919>. <https://www.rfc-editor.org/info/rfc1919>.
[RFC1928] Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D., and [RFC1928] Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D., and
L. Jones, "SOCKS Protocol Version 5", RFC 1928, L. Jones, "SOCKS Protocol Version 5", RFC 1928,
DOI 10.17487/RFC1928, March 1996, DOI 10.17487/RFC1928, March 1996,
<https://www.rfc-editor.org/info/rfc1928>. <https://www.rfc-editor.org/info/rfc1928>.
[RFC2018] Mathis, M., Mahdavi, J., Floyd, S., and A. Romanow, "TCP [RFC2018] Mathis, M., Mahdavi, J., Floyd, S., and A. Romanow, "TCP
Selective Acknowledgment Options", RFC 2018, DOI 10.17487/ Selective Acknowledgment Options", RFC 2018,
RFC2018, October 1996, DOI 10.17487/RFC2018, October 1996,
<https://www.rfc-editor.org/info/rfc2018>. <https://www.rfc-editor.org/info/rfc2018>.
[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering: [RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827, Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827,
May 2000, <https://www.rfc-editor.org/info/rfc2827>. May 2000, <https://www.rfc-editor.org/info/rfc2827>.
[RFC3135] Border, J., Kojo, M., Griner, J., Montenegro, G., and Z. [RFC3135] Border, J., Kojo, M., Griner, J., Montenegro, G., and Z.
Shelby, "Performance Enhancing Proxies Intended to Shelby, "Performance Enhancing Proxies Intended to
Mitigate Link-Related Degradations", RFC 3135, Mitigate Link-Related Degradations", RFC 3135,
DOI 10.17487/RFC3135, June 2001, DOI 10.17487/RFC3135, June 2001,
<https://www.rfc-editor.org/info/rfc3135>. <https://www.rfc-editor.org/info/rfc3135>.
[RFC6181] Bagnulo, M., "Threat Analysis for TCP Extensions for [RFC6181] Bagnulo, M., "Threat Analysis for TCP Extensions for
Multipath Operation with Multiple Addresses", RFC 6181, Multipath Operation with Multiple Addresses", RFC 6181,
DOI 10.17487/RFC6181, March 2011, DOI 10.17487/RFC6181, March 2011,
<https://www.rfc-editor.org/info/rfc6181>. <https://www.rfc-editor.org/info/rfc6181>.
[RFC6555] Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with [RFC6555] Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
Dual-Stack Hosts", RFC 6555, DOI 10.17487/RFC6555, Dual-Stack Hosts", RFC 6555, DOI 10.17487/RFC6555, April
April 2012, <https://www.rfc-editor.org/info/rfc6555>. 2012, <https://www.rfc-editor.org/info/rfc6555>.
[RFC6887] Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and [RFC6887] Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
P. Selkirk, "Port Control Protocol (PCP)", RFC 6887, P. Selkirk, "Port Control Protocol (PCP)", RFC 6887,
DOI 10.17487/RFC6887, April 2013, DOI 10.17487/RFC6887, April 2013,
<https://www.rfc-editor.org/info/rfc6887>. <https://www.rfc-editor.org/info/rfc6887>.
[RFC7323] Borman, D., Braden, B., Jacobson, V., and R. [RFC6928] Chu, J., Dukkipati, N., Cheng, Y., and M. Mathis,
"Increasing TCP's Initial Window", RFC 6928,
DOI 10.17487/RFC6928, April 2013,
<https://www.rfc-editor.org/info/rfc6928>.
[RFC6978] Touch, J., "A TCP Authentication Option Extension for NAT
Traversal", RFC 6978, DOI 10.17487/RFC6978, July 2013,
<https://www.rfc-editor.org/info/rfc6978>.
[RFC7323] Borman, D., Braden, B., Jacobson, V., and R.
Scheffenegger, Ed., "TCP Extensions for High Performance", Scheffenegger, Ed., "TCP Extensions for High Performance",
RFC 7323, DOI 10.17487/RFC7323, September 2014, RFC 7323, DOI 10.17487/RFC7323, September 2014,
<https://www.rfc-editor.org/info/rfc7323>. <https://www.rfc-editor.org/info/rfc7323>.
[RFC7414] Duke, M., Braden, R., Eddy, W., Blanton, E., and A. [RFC7414] Duke, M., Braden, R., Eddy, W., Blanton, E., and A.
Zimmermann, "A Roadmap for Transmission Control Protocol Zimmermann, "A Roadmap for Transmission Control Protocol
(TCP) Specification Documents", RFC 7414, DOI 10.17487/ (TCP) Specification Documents", RFC 7414,
RFC7414, February 2015, DOI 10.17487/RFC7414, February 2015,
<https://www.rfc-editor.org/info/rfc7414>. <https://www.rfc-editor.org/info/rfc7414>.
Appendix A. Differences with SOCKSv5
The description above is a simplified description of the Converter
protocol. At a first glance, the proposed solution could seem
similar to the SOCKS v5 protocol [RFC1928]. This protocol is used to
proxy TCP connections. The Client creates a connection to a SOCKS
proxy, exchanges authentication information and indicates the
destination address and port of the final server. At this point, the
SOCKS proxy creates a connection towards the final server and relays
all data between the two proxied connections. The operation of an
implementation based on SOCKSv5 is illustrated in Figure 20.
Client SOCKS Proxy Server
-------------------->
SYN
<--------------------
SYN+ACK
-------------------->
ACK
-------------------->
Version=5, Auth Methods
<--------------------
Method
-------------------->
Auth Request (unless "No auth" method negotiated)
<--------------------
Auth Response
-------------------->
Connect Server:Port -------------------->
SYN
<--------------------
SYN+ACK
<--------------------
Succeeded
-------------------->
Data1
-------------------->
Data1
<--------------------
Data2
<--------------------
Data2
Figure 20: Establishment of a TCP connection through a SOCKS proxy
without authentication
The Converter protocol also relays data between an upstream and a
downstream connection, but there are important differences with
SOCKSv5.
A first difference is that the Converter protocol leverages the TFO
option [RFC7413] to exchange all control information during the
three-way handshake. This reduces the connection establishment delay
compared to SOCKS that requires two or more round-trip-times before
the establishment of the downstream connection towards the final
destination. In today's Internet, latency is a important metric and
various protocols have been tuned to reduce their latency
[I-D.arkko-arch-low-latency]. A recently proposed extension to SOCKS
also leverages the TFO option [I-D.olteanu-intarea-socks-6].
A second difference is that the Converter protocol explicitly takes
the TCP extensions into account. By using the Converter protocol,
the Client can learn whether a given TCP extension is supported by
the destination Server. This enables the Client to bypass the
Transport Converter when the destination supports the required TCP
extension. Neither SOCKS v5 [RFC1928] nor the proposed SOCKS v6
[I-D.olteanu-intarea-socks-6] provide such a feature.
A third difference is that a Transport Converter will only accept the
connection initiated by the Client provided that the downstream
connection is accepted by the Server. If the Server refuses the
connection establishment attempt from the Transport Converter, then
the upstream connection from the Client is rejected as well. This
feature is important for applications that check the availability of
a Server or use the time to connect as a hint on the selection of a
Server [RFC6555].
Authors' Addresses Authors' Addresses
Olivier Bonaventure Olivier Bonaventure (editor)
Tessares Tessares
Email: Olivier.Bonaventure@tessares.net Email: Olivier.Bonaventure@tessares.net
Mohamed Boucadair Mohamed Boucadair (editor)
Orange Orange
Email: mohamed.boucadair@orange.com Email: mohamed.boucadair@orange.com
Bart Peirens Bart Peirens
Proximus Proximus
Email: bart.peirens@proximus.com Email: bart.peirens@proximus.com
SungHoon Seo SungHoon Seo
skipping to change at page 33, line 26 skipping to change at page 37, line 4
Bart Peirens Bart Peirens
Proximus Proximus
Email: bart.peirens@proximus.com Email: bart.peirens@proximus.com
SungHoon Seo SungHoon Seo
Korea Telecom Korea Telecom
Email: sh.seo@kt.com Email: sh.seo@kt.com
Anandatirtha Nandugudi Anandatirtha Nandugudi
Tessares Memphis University
Email: anand.nandugudi@tessares.net Email: nndugudi@memphis.edu
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