draft-ietf-dhc-relay-port-06.txt   draft-ietf-dhc-relay-port-07.txt 
Networking Working Group N. Shen Networking Working Group N. Shen
Internet-Draft E. Chen Internet-Draft E. Chen
Intended status: Standards Track Cisco Systems Intended status: Standards Track Cisco Systems
Expires: March 1, 2018 August 28, 2017 Expires: April 30, 2018 October 27, 2017
Generalized UDP Source Port for DHCP Relay Generalized UDP Source Port for DHCP Relay
draft-ietf-dhc-relay-port-06 draft-ietf-dhc-relay-port-07
Abstract Abstract
This document proposes an extension to the DHCP protocols that allows This document proposes an extension to the DHCP protocols that allows
a relay agent to receive packets from a server or an upstream relay a relay agent to use any available source port for upstream
agent on any UDP port, not just the default port 67 for IPv4 or communications, and to include a DHCP option that can be used to
default port 547 for IPv6. statelessly route responses back to the appropriate source port on
downstream communications.
Status of This Memo 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 http://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 March 1, 2018. This Internet-Draft will expire on April 30, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 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
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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3. Changes to DHCP Specifications . . . . . . . . . . . . . . . 3 3. Changes to DHCP Specifications . . . . . . . . . . . . . . . 3
3.1. Changes to DHCPv4 in RFC 2131 . . . . . . . . . . . . . . 3 3.1. Changes to DHCPv4 in RFC 2131 . . . . . . . . . . . . . . 3
3.2. Changes to DHCPv6 in RFC 3315 . . . . . . . . . . . . . . 4 3.2. Changes to DHCPv6 in RFC 3315 . . . . . . . . . . . . . . 4
4. Relay Source Port Sub-option and Option . . . . . . . . . . . 4 4. Relay Source Port Sub-option and Option . . . . . . . . . . . 4
4.1. Source Port Sub-option for DHCPv4 . . . . . . . . . . . . 4 4.1. Source Port Sub-option for DHCPv4 . . . . . . . . . . . . 4
4.2. Relay Source Port Option for DHCPv6 . . . . . . . . . . . 5 4.2. Relay Source Port Option for DHCPv6 . . . . . . . . . . . 5
5. Relay Agent and Server Behavior . . . . . . . . . . . . . . . 6 5. Relay Agent and Server Behavior . . . . . . . . . . . . . . . 6
5.1. DHCPv4 . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.1. DHCPv4 . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.2. DHCPv6 . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.2. DHCPv6 . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.3. Compatibility . . . . . . . . . . . . . . . . . . . . . . 7 5.3. Compatibility . . . . . . . . . . . . . . . . . . . . . . 7
5.4. Deployment Considerations . . . . . . . . . . . . . . . . 7
6. An IPv6 Cascaded Relay Example . . . . . . . . . . . . . . . 7 6. An IPv6 Cascaded Relay Example . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8 8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
10. Normative References . . . . . . . . . . . . . . . . . . . . 9 10. Normative References . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction 1. Introduction
RFC 2131 [RFC2131] and RFC 3315 [RFC3315] specify the use of UDP as RFC 2131 [RFC2131] and RFC 3315 [RFC3315] specify the use of UDP as
the transport protocol for DHCP. They also define both the server the transport protocol for DHCP. They also define both the server
side and client side port numbers. The IPv4 server port is UDP side and client side port numbers. The IPv4 server port is UDP
number (67) and the client port is UDP number (68); for IPv6 the number (67) and the client port is UDP number (68); for IPv6 the
server port is (546) and the client port is (547). server port is (546) and the client port is (547).
This fixed UDP port of DHCP protocol scheme creates challenges in The fixed UDP port combinations for the DHCP protocol scheme creates
certain DHCP relay operations. For instance, in a large scale DHCP challenges in certain DHCP relay operations. For instance, in a
relay implementation on a single switch node, the DHCP relay large scale DHCP relay implementation on a single switch node, the
functionality may be partitioned among multiple relay processes. All DHCP relay functionality may be partitioned among multiple relay
these DHCP relay processes may share the same IP address of the processes. All these DHCP relay processes may share the same IP
switch node. If the UDP source port has to be a fixed number as address of the switch node. If the UDP source port has to be a fixed
currently specified, the transport socket operation of DHCP packets number as currently specified, the transport socket operation of DHCP
would need to go through a central entity or process which would packets would need to go through a central entity or process which
defeat the purpose of distributing DHCP relay functionality. would defeat the purpose of distributing DHCP relay functionality.
In some large-scale deployment, the decision to split the DHCP In some large-scale deployment, the decision to split the DHCP
functionality into multiple processes on a node may not be purely functionality into multiple processes on a node may not be purely
based on DHCP relay computational load. But rather DHCP relay could based on DHCP relay computational load. But rather DHCP relay could
just be one of the functions in a multi-process implementation. just be one of the functions in a multi-process implementation.
Although assigning a different IP/IPv6 source address for each DHCP Although assigning a different IPv4/IPv6 source address for each DHCP
relay process can be a solution, it would introduce operational and relay process can be a solution, it would introduce operational and
network management complexities, especially given the scarceness of network management complexities, especially given the scarceness of
the IPv4 addresses. the IPv4 addresses.
This document proposes an extension to relax the fixed UDP source This document proposes an extension to relax the fixed UDP source
port requirement for the DHCP relay agents. This extension requires port requirement for the DHCP relay agents. This extension requires
a DHCP server to remember the inbound packet's UDP port number along a DHCP server to remember the inbound packet's UDP port number along
with the IP/IPv6 address. The DHCP server when sending back replies with the IPv4/IPv6 address. The DHCP server when sending back
MUST use the UDP port number that the incoming relay agent uses replies MUST use the UDP port number that the incoming relay agent
instead of the fixed DHCP port number. In the case of IPv6 cascaded uses instead of the fixed DHCP port number. In the case of IPv6
relay agents [RFC3315], the upstream relay agent needs to use the cascaded relay agents [RFC3315], the upstream relay agent needs to
"Relay Source Port Option" to record the downstream source port and use the "Relay Source Port Option" to record the downstream source
it MUST use this recorded port number instead of the fixed DHCP port port and it MUST use this recorded port number instead of the fixed
number when replaying the reply messages. DHCP port number when replaying the reply messages.
1.1. Requirements Language 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
2. Terminology 2. Terminology
Downstream Device: In the DHCP relay context, it refers to the next Downstream Device: In the DHCP relay context, it refers to the next
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downstream relay agent. downstream relay agent.
5.3. Compatibility 5.3. Compatibility
Sites that need for relay agents to specify a source port will need Sites that need for relay agents to specify a source port will need
to install new DHCP server and DHCP relay agent software with this to install new DHCP server and DHCP relay agent software with this
feature. If a site installs only DHCP relay agent software with this feature. If a site installs only DHCP relay agent software with this
feature, there is no possibility that the DHCP server will be able to feature, there is no possibility that the DHCP server will be able to
communicate to the relay agent. communicate to the relay agent.
The implementation is advised to allow configuration for relay agent 5.4. Deployment Considerations
specifying a DHCP relay port number. It can be used to allow the
relay agent either using a normal DHCP UDP port or non-DHCP UDP port. During deployment, it may be advisable the operator and/or user of
the new DHCP relay port implementation upgrade the DHCP server first
when possible, before the relay implementations are deployed. This
would ensure that the erroneous case noted in Section 5.3 is not
encountered.
When the DHCP relay port implementation is deployed, it is
recommended that the configuration is setup to allow for the mode of
operation where a non-DHCP port can be used for the DHCP relay
agents. The recommended configuration then permits the relay agent
to utilize the default DHCP UDP port, or a non-DHCP UDP port as
desired.
Although if the network uses firewall to block or allow DHCP packets
with both static UDP source and destination port numbers, this may no
longer match the packets from new DHCP relay agent and server
software with this extension. The firewall rules need to be modified
only to match the DHCP server side of the UDP port number, and if
necessary, IP addresses and other attributes.
6. An IPv6 Cascaded Relay Example 6. An IPv6 Cascaded Relay Example
An example of IPv6 cascaded relay agents with the "Relay Source Port An example of IPv6 cascaded relay agents with the "Relay Source Port
Option" is shown below. Option" is shown below.
(forward) (forward) (forward) (forward) (forward) (forward)
Relay1 ----------> Relay2 ----------> Relay3 ----------> Server Relay1 ----------> Relay2 ----------> Relay3 ----------> Server
(1000) (547) (547) (1000) (547) (547)
(reply) (reply) (reply) (reply) (reply) (reply)
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Port Option", it finds the "Downstream Source Port" field has the Port Option", it finds the "Downstream Source Port" field has the
value of 1000. Relay2 then uses this port number in the UDP packet value of 1000. Relay2 then uses this port number in the UDP packet
when sending the Relay-reply message to Relay1. when sending the Relay-reply message to Relay1.
When Relay1 receives the Relay-reply message with the "Relay Source When Relay1 receives the Relay-reply message with the "Relay Source
Port Option", it finds that the "Downstream Source Port" field has Port Option", it finds that the "Downstream Source Port" field has
the value of zero. Relay1 then uses the normal IPv6 port 547 in the the value of zero. Relay1 then uses the normal IPv6 port 547 in the
packet sending the Relay-reply message to its downstream relay agent packet sending the Relay-reply message to its downstream relay agent
or uses UDP port 546 to an IPv6 client. or uses UDP port 546 to an IPv6 client.
This DHCP extension works with any combination of IPv6 cascaded relay
agents, as long as the relay agent which uses a non-DHCP UDP port
(not 547) and its upstream relay device support this generalized UDP
source port extension.
Similar to the above example, now assume that Relay2 uses the UDP
source port of 2000 instead of 547 as in the diagram. The Relay3
device needs to support this DHCP extension and it will set 2000 in
its "Downstream Source Port" field of the option in the Relay-forward
message. When DHCP server sends the DHCP Relay-reply to Relay3,
Relay3 finds its own relay option has this "Downstream Source Port"
with the value of 2000. Relay3 will use this UDP port when sending
the Relay-reply message to Relay2.
7. IANA Considerations 7. IANA Considerations
A new sub-option, DHCPv4 Relay Source Port, is defined in this A new sub-option, DHCPv4 Relay Source Port, is defined in this
document within the IPv4 Relay Agent Information Option. It needs to document within the IPv4 Relay Agent Information Option. It needs to
be assigned by IANA in the "DHCP Relay Agent Sub-Option Codes" be assigned by IANA in the "DHCP Relay Agent Sub-Option Codes"
registry, http://www.iana.org/assignments/bootp-dhcp-parameters as registry, http://www.iana.org/assignments/bootp-dhcp-parameters as
specified in [RFC3046]. specified in [RFC3046].
A new option, DHCPv6 Relay Source Port, is defined in this document A new option, DHCPv6 Relay Source Port, is defined in this document
for DHCPv6 and it needs to be assigned by IANA for the DHCPv6 option for DHCPv6 and it needs to be assigned by IANA for the DHCPv6 option
code, in the "Option Codes" registry for DHCPv6, code, in the "Option Codes" registry for DHCPv6,
http://www.iana.org/assignments/dhcpv6-parameters as specified in http://www.iana.org/assignments/dhcpv6-parameters as specified in
[RFC3315]. [RFC3315].
8. Security Considerations 8. Security Considerations
[RFC3118] and [RFC3315] described many of the threats in using DHCP. [RFC3118] and [RFC3315] described many of the threats in using DHCP.
This extension does not raise addition security issues. This extension does not raise addition security issues.
Although if the network uses firewall to block or allow DHCP packets
with both static UDP source and destination port numbers, this may no
longer match the packets from new DHCP relay agent and server
software. The firewall rules need to be modified only to match the
DHCP server side of the UDP port number, and if necessary, IP
addresses and other attributes.
9. Acknowledgments 9. Acknowledgments
The authors would like to thank Peter Arberg, Luyuan Fang, Bhanu The authors would like to thank Peter Arberg, Luyuan Fang, Bhanu
Gopalasetty, Andre Kostur, Ted Lemon, Kishore Seshadri and Jackelyn Gopalasetty, Scott Kelly, Andre Kostur, Victor Kuarsingh, Ted Lemon,
Shen for their review and comments of this document. Kishore Seshadri and Jackelyn Shen for their review and comments of
this document.
The authors would like to thank Bernie Volz for discussions that led The authors would like to thank Bernie Volz for discussions that led
to the definition of The Relay Source Port sub-option and DHCPv6 to the definition of The Relay Source Port sub-option and DHCPv6
Relay Source Port Option. Relay Source Port Option.
The RFC text was produced using Marshall Rose's xml2rfc tool. The RFC text was produced using Marshall Rose's xml2rfc tool.
10. Normative References 10. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
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