draft-ietf-dhc-relay-port-10.txt   rfc8357.txt 
Networking Working Group N. Shen Internet Engineering Task Force (IETF) N. Shen
Internet-Draft E. Chen Request for Comments: 8357 E. Chen
Intended status: Standards Track Cisco Systems Category: Standards Track Cisco Systems
Expires: June 17, 2018 December 14, 2017 ISSN: 2070-1721 March 2018
Generalized UDP Source Port for DHCP Relay Generalized UDP Source Port for DHCP Relay
draft-ietf-dhc-relay-port-10
Abstract Abstract
This document proposes an extension to the DHCP protocols that allows This document defines an extension to the DHCP protocols that allows
a relay agent to use any available source port for upstream a relay agent to use any available source port for upstream
communications, and to include a DHCP option that can be used to communications. The extension also allows inclusion of a DHCP option
statelessly route responses back to the appropriate source port on that can be used to statelessly route responses back to the
downstream communications. 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 is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
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Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on June 17, 2018. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8357.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Changes to DHCP Specifications . . . . . . . . . . . . . . . 3 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
3.1. Additions to DHCPv4 in RFC 2131 . . . . . . . . . . . . . 3 2.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 3
3. Changes to DHCP Specifications . . . . . . . . . . . . . . . 4
3.1. Additions to DHCPv4 in RFC 2131 . . . . . . . . . . . . . 4
3.2. Additions to DHCPv6 in RFC 3315 . . . . . . . . . . . . . 4 3.2. Additions 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 . . . . . . . . . . . . 5
4.2. Relay Source Port Option for DHCPv6 . . . . . . . . . . . 5 4.2. Relay Source Port Option for DHCPv6 . . . . . . . . . . . 5
5. Relay Agent and Server Behavior . . . . . . . . . . . . . . . 5 5. Relay Agent and Server Behavior . . . . . . . . . . . . . . . 6
5.1. DHCPv4 . . . . . . . . . . . . . . . . . . . . . . . . . 5 5.1. DHCPv4 . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.2. DHCPv6 . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.2. DHCPv6 . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.3. Compatibility . . . . . . . . . . . . . . . . . . . . . . 6 5.3. Compatibility . . . . . . . . . . . . . . . . . . . . . . 7
5.4. Deployment Considerations . . . . . . . . . . . . . . . . 7 5.4. Deployment Considerations . . . . . . . . . . . . . . . . 7
6. An IPv6 Cascaded Relay Example . . . . . . . . . . . . . . . 7 6. Example of an IPv6-Cascaded Relay . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9 8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 9. Normative References . . . . . . . . . . . . . . . . . . . . 9
10. Normative References . . . . . . . . . . . . . . . . . . . . 9 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 10
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 and client-side port numbers. The IPv4 server port is UDP number
number (67) and the client port is UDP number (68); for IPv6 the (67) and the client port is UDP number (68); for IPv6, the server
server port is (547) and the client port is (546). port is (547) and the client port is (546).
The fixed UDP port combinations for the DHCP protocol scheme creates The fixed UDP port combinations for the DHCP protocol scheme creates
challenges in certain DHCP relay operations. For instance, in a challenges in certain DHCP relay operations. For instance, in a
large scale DHCP relay implementation on a single switch node, the large-scale DHCP relay implementation on a single-switch node, the
DHCP relay functionality may be partitioned among multiple relay DHCP relay functionality may be partitioned among multiple relay
processes. All these DHCP relay processes may share the same IP processes. All of these DHCP relay processes may share the same IP
address of the switch node. If the UDP source port has to be a fixed address of the switch node. If the UDP source port has to be a fixed
number as currently specified, the transport socket operation of DHCP number as currently specified, the transport socket operation of DHCP
packets would need to go through a central entity or process which packets would need to go through a central entity or process, which
would 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 deployments, 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. 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 IPv4/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, this would introduce operational and
network management complexities, especially given the scarceness of network management complexities, especially given the scarceness of
the IPv4 addresses. IPv4 addresses.
This document proposes an extension to relax the fixed UDP source This document defines an extension to relax the fixed UDP source port
port requirement for the DHCP relay agents. This extension requires requirement for the DHCP relay agents. This extension requires a
a DHCP server to remember the inbound packet's UDP port number along DHCP server to remember the inbound packet's UDP port number along
with the IPv4/IPv6 address. The DHCP server when sending back with the IPv4/IPv6 address. When sending back replies, the DHCP
replies MUST use the UDP port number that the incoming relay agent server MUST use the UDP port number that the incoming relay agent
uses instead of the fixed DHCP port number. In the case of IPv6 uses instead of the fixed DHCP port number. In the case of
cascaded relay agents [RFC3315], the upstream relay agent needs to IPv6-cascaded relay agents [RFC3315], the upstream relay agent needs
use the "Relay Source Port Option" to record the downstream source to use the "Relay Source Port Option" to record the downstream source
port and it MUST use this recorded port number instead of the fixed port, and it MUST use this recorded port number instead of the fixed
DHCP port number when replaying the reply messages. DHCP port number when replaying the reply messages.
1.1. Requirements Language 2. Terminology
2.1. 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", "NOT RECOMMENDED", "MAY", and
document are to be interpreted as described in RFC 2119 [RFC2119]. "OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Terminology 2.2. Definitions
Downstream Device: In the DHCP relay context, it refers to the next Downstream Device: In the DHCP relay context, this refers to the
relay agent for forwarding Relay-reply Messages. next relay agent that forwards Relay-reply messages.
Upstream Device: In the DHCP relay context, it refers to the next Upstream Device: In the DHCP relay context, this refers to the next
relay agent or DHCP server for forwarding Relay-forward relay agent or DHCP server that forwards Relay-forward messages.
Messages.
Relay Source Port: This is the UDP port that a relay agent uses to Relay Source Port: This is the UDP port that a relay agent uses to
receive Relay-forward Messages from an upstream device. receive Relay-forward messages from an upstream device.
Downstream Source Port: This is the UDP port that the downstream Downstream Source Port: This is the UDP port that the downstream
device uses when forwarding Relay-forward Messages to this device uses when forwarding Relay-forward messages to this relay
relay agent device. This UDP port is to be used by this agent device. This UDP port is to be used by this relay agent
relay agent device when forwarding the Relay-reply Messages device when forwarding the Relay-reply messages to that downstream
to that downstream device. device.
Non-DHCP UDP Port: Any valid and non-zero UDP port other than port Non-DHCP UDP Port: Any valid and non-zero UDP port other than port
67 for DHCPv4 and port 547 for DHCPv6. 67 for DHCPv4 and port 547 for DHCPv6.
3. Changes to DHCP Specifications 3. Changes to DHCP Specifications
3.1. Additions to DHCPv4 in RFC 2131 3.1. Additions to DHCPv4 in RFC 2131
Section 4.1 of RFC 2131 [RFC2131] specifies that: Section 4.1 of RFC 2131 [RFC2131] specifies that:
DHCP uses UDP as its transport protocol. DHCP messages from a DHCP uses UDP as its transport protocol. DHCP messages from a
client to a server are sent to the 'DHCP server' port (67), and client to a server are sent to the 'DHCP server' port (67), and
DHCP messages from a server to a client are sent to the 'DHCP DHCP messages from a server to a client are sent to the 'DHCP
client' port (68). client' port (68).
Relay agents implementing this specification may be configured Relay agents implementing this specification may be configured
instead to use a source port number other than 67 when relaying instead to 1) use a source port number other than 67 when relaying
messages toward servers, and to receive responses toward clients on messages toward servers and 2) receive responses toward clients on
that same port. This will only work when the DHCP server or relay that same port. This will only work when the DHCP server or relay
agent to which such a relay agent is forwarding messages is upgraded agent to which such a relay agent is forwarding messages is upgraded
to support this extension. to support this extension.
3.2. Additions to DHCPv6 in RFC 3315 3.2. Additions to DHCPv6 in RFC 3315
Section 5.2 of RFC 3315 [RFC3315] specifies that: Section 5.2 of RFC 3315 [RFC3315] specifies that:
Clients listen for DHCP messages on UDP port 546. Servers and Clients listen for DHCP messages on UDP port 546. Servers and
relay agents listen for DHCP messages on UDP port 547. relay agents listen for DHCP messages on UDP port 547.
Relay agents implementing this specification may be configured Relay agents implementing this specification may be configured
instead to use a source port number other than 547 when relaying instead to 1) use a source port number other than 547 when relaying
messages toward servers, and to receive responses toward clients on messages toward servers and 2) receive responses toward clients on
that same port. This will only work when the DHCP server or relay that same port. This will only work when the DHCP server or relay
agent to which such a relay agent is forwarding messages is upgraded agent to which such a relay agent is forwarding messages is upgraded
to support this extension. to support this extension.
4. Relay Source Port Sub-option and Option 4. Relay Source Port Sub-option and Option
Relay agents do not maintain state. To return a message to its Relay agents do not maintain state. To return a message to its
source, the relay agent must include all the required information in source, the relay agent must include all the required information in
the Relay-Forward message. When a relay in a sequence of cascaded the Relay-forward message. When a relay in a sequence of cascaded
relays does not use the standard source port, that source port must relays does not use the standard source port, that source port must
be included along with the source address. This option allows the be included along with the source address. This option allows the
relay agent to do so. relay agent to do so.
4.1. Source Port Sub-option for DHCPv4 4.1. Source Port Sub-option for DHCPv4
The Relay Agent "Source Port Sub-option" is a new option, and it is The relay agent "Source Port Sub-option" is a new option, and it is
part of the relay-agent-information option for DHCPv4 [RFC3046]. part of the "Relay Agent Information" option for DHCPv4 [RFC3046].
The format of the "Source Port Sub-option" is shown below: The format of the "Source Port Sub-option" is shown below:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SubOpt Code | Len | | SubOpt Code | Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where: Where:
SubOpt Code: SUBOPT_RELAY_PORT. 8 bit value, to be assigned by SubOpt Code: SUBOPT_RELAY_PORT. 8-bit value, 19.
IANA.
Len: 8 bit value to be set to 0. Len: 8-bit value to be set to 0.
4.2. Relay Source Port Option for DHCPv6 4.2. Relay Source Port Option for DHCPv6
The "Relay Source Port Option" is a new DHCPv6 option. It MUST be The "Relay Source Port Option" is a new DHCPv6 option. It MUST be
used either by a DHCPv6 relay agent that uses a non-DHCP UDP port used by either 1) a DHCPv6 relay agent that uses a non-DHCP UDP port
(not 547) communicating with the IPv6 server and the upstream relay (not 547) communicating with the IPv6 server and the upstream relay
agent, or by a IPv6 relay agent that detects the use of a non-DHCP agent or 2) an IPv6 relay agent that detects the use of a non-DHCP
UDP port (not 547) by a downstream relay agent. UDP port (not 547) by a downstream relay agent.
The format of the "Relay Source Port Option" is shown below: The format of the "Relay Source Port Option" is shown below:
0 1 2 3 0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_RELAY_RELAY_PORT | Option-Len | | OPTION_RELAY_PORT | Option-Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream Source Port | | Downstream Source Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where: Where:
Option-Code: OPTION_RELAY_RELAY_PORT. 16 bit value, to be Option-Code: OPTION_RELAY_PORT. 16-bit value, 135.
assigned by IANA.
Option-Len: 16 bit value to be set to 2. Option-Len: 16-bit value to be set to 2.
Downstream Source Port: 16 bit value. To be set by the IPv6 Downstream Source Port: 16-bit value. To be set by the IPv6 relay
relay either to the downstream relay agent's UDP source either to the downstream relay agent's UDP source port used for
port used for the UDP packet, or to zero if only the the UDP packet, or to zero if only the local relay agent uses the
local relay agent uses the non-DHCP UDP port (not 547). non-DHCP UDP port (not 547).
5. Relay Agent and Server Behavior 5. Relay Agent and Server Behavior
5.1. DHCPv4 5.1. DHCPv4
When a relay agent uses a non-DHCP UDP port (not 67) communicating When a relay agent uses a non-DHCP UDP port (not 67) to communicate
with the DHCP server, it MUST include the "Source Port Sub-option" in with the DHCP server, it MUST include the "Source Port Sub-option" in
Relay-forward messages to indicate that. Relay-forward messages to indicate that.
When an IPv4 server receives a message from a relay agent with the When an IPv4 server receives a message from a relay agent with the
"Source Port Sub-option", it MUST remember the UDP source port of the "Source Port Sub-option", it MUST remember the UDP source port of the
message and use that port number as the UDP destination port when message and use that port number as the UDP destination port when
sending the reply message to the same relay agent. sending the reply message to the same relay agent.
5.2. DHCPv6 5.2. DHCPv6
The IPv6 relay agent MUST include the "Relay Source Port Option" when The IPv6 relay agent MUST include the "Relay Source Port Option" when
it uses a non-DHCP UDP port (not 547) to communicate to a DHCPv6 it uses a non-DHCP UDP port (not 547) to communicate to a DHCPv6
server or an upstream IPv6 relay agent. Also when an IPv6 relay server or an upstream IPv6 relay agent. Also, when an IPv6 relay
agent detects that a downstream relay agent uses a non-DHCP UDP port agent detects that a downstream relay agent uses a non-DHCP UDP port
in the packet, it MUST record the port number in the "Downstream in the packet, it MUST record the port number in the "Downstream
Source Port" field of this option. If this option is included to Source Port" field of this option. If this option is included to
indicate only the local non-DHCP UDP port usage and there is no indicate only the local non-DHCP UDP port usage and the port is not
downstream relay agent's non-DHCP UDP port usage, the field being used by a downstream relay agent, the Downstream Source Port
Downstream Source Port field MUST be set to zero. field MUST be set to zero.
The IPv6 relay agent MUST include this option in the following three The IPv6 relay agent MUST include this option in the following three
cases: cases:
1) The local relay agent uses a non-DHCP UDP port (not 547). 1. The local relay agent uses a non-DHCP UDP port (not 547).
2) the downstream relay agent uses a non-DHCP UDP port (not 547). 2. The downstream relay agent uses a non-DHCP UDP port (not 547).
3) the local relay agent and the downstream relay agent both use 3. The local relay agent and the downstream relay agent both use
non-DHCP UDP ports (not 547). non-DHCP UDP ports (not 547).
In the first case, the value of the "Downstream Source Port" field is In the first case, the value of the "Downstream Source Port" field is
set to zero. In the other two cases, the value of the field is set set to zero. In the other two cases, the value of the field is set
to the UDP port number that the downstream relay agent uses. to the UDP port number that the downstream relay agent uses.
When an IPv6 server receives a Relay-forward message with the "Relay When an IPv6 server receives a Relay-forward message with the "Relay
Source Port Option", it MUST copy the option when constructing the Source Port Option", it MUST copy the option when constructing the
Relay-reply chain in response to the Relay-forward message. This Relay-reply chain in response to the Relay-forward message. This
option MUST NOT appear in any message other than a Relay-forward or option MUST NOT appear in any message other than a Relay-forward or
Relay-reply message. Additionally, the IPv6 server MUST check and Relay-reply message. Additionally, the IPv6 server MUST check and
skipping to change at page 6, line 49 skipping to change at page 7, line 13
message in replying to the relay agent. message in replying to the relay agent.
When a relay agent receives a Relay-reply message with the "Relay When a relay agent receives a Relay-reply message with the "Relay
Source Port Option" from a server or from an upstream relay agent, if Source Port Option" from a server or from an upstream relay agent, if
the "Downstream Source Port" field in the option is non-zero, it MUST the "Downstream Source Port" field in the option is non-zero, it MUST
use this UDP port number to forward the Relay-reply message to the use this UDP port number to forward the Relay-reply message to the
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 relay agents to specify a source port need to install
to install new DHCP server and DHCP relay agent software with this new DHCP server and DHCP relay agent software with this feature. If
feature. If a site installs only DHCP relay agent software with this a site installs only DHCP relay agent software with this feature,
feature, there is no possibility that the DHCP server will be able to there is no possibility that the DHCP server will be able to
communicate to the relay agent. communicate to the relay agent.
5.4. Deployment Considerations 5.4. Deployment Considerations
During deployment, it is advisable the operator and/or user of the During deployment, the operator and/or user of the new DHCP play port
new DHCP relay port implementation upgrade the DHCP server first when implementation should upgrade the DHCP server before the relay
possible, before the relay implementations are deployed. This would implementations are deployed. This would ensure that the erroneous
ensure that the erroneous case noted in Section 5.3 is not case noted in Section 5.3 is not encountered. If the upstream relay
encountered. If the upstream relay agent or server does not support agent or server does not support this extension, this DHCP relay port
this extension, this DHCP relay port feature needs to be disabled. feature needs to be disabled.
When the DHCP relay port implementation is deployed, the default When the DHCP relay port implementation is deployed, the default
relay agent behavior should use the DHCP UDP port, it is recommended relay agent behavior should use the DHCP UDP port, and it is
that the configuration is setup to allow for the mode of operation recommended that the configuration be set up to allow for the mode of
where a non-DHCP port can be used for the DHCP relay agents. operation where a non-DHCP port can be used for the DHCP relay
agents.
Although if the network uses firewall to block or allow DHCP packets If the network uses a firewall to block or allow DHCP packets with
with both static UDP source and destination port numbers, this may no both static UDP source and destination port numbers, this may no
longer match the packets from new DHCP relay agent and server longer match the packets from new DHCP relay agent and server
software with this extension. The firewall rules need to be modified 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 to match only the DHCP server side of the UDP port number and, if
necessary, IP addresses and other attributes. necessary, IP addresses and other attributes.
6. An IPv6 Cascaded Relay Example 6. Example of an IPv6-Cascaded Relay
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)
<---------- <---------- <---------- <---------- <---------- <----------
In the above diagram, all the IPv6 devices support this generalized In the above diagram, all the IPv6 devices support this generalized
UDP source port extension except for Relay3. Relay1 is the only UDP source port extension except for Relay3. Relay1 is the only
relay agent device uses a non-DHCP UDP port (not 547). Relay2 is the relay agent device that uses a non-DHCP UDP port (not 547). Relay2
upstream device of Relay1. is the upstream device of Relay1.
Both Relay1 and Relay2 include the "Relay Source Port Option" in Both Relay1 and Relay2 include the "Relay Source Port Option" in the
Relay-forward message. Relay1 sets the "Downstream Source Port" Relay-forward message. Relay1 sets the "Downstream Source Port"
field in the option to zero. Relay2 notices the "Relay Source Port field in the option to zero. Relay2 notices that the "Relay Source
Option" is included in the message from Relay1, and it determines Port Option" is included in the message from Relay1, and it
that the UDP source port used by Relay1 is 1000. Relay2 will include determines that the UDP source port used by Relay1 is 1000. Relay2
the "Relay Source Port Option" and it sets the "Downstream Source will include the "Relay Source Port Option", and it sets the
Port" field in the option to 1000. The IPv6 server copies the "Relay "Downstream Source Port" field in the option to 1000. The IPv6
Source Port Option" when replying with the Relay-reply message. server copies the "Relay Source Port Option" when replying with the
Relay-reply message.
When Relay2 receives the Relay-reply message with the "Relay Source When Relay2 receives the Relay-reply message with the "Relay Source
Port Option", it finds the "Downstream Source Port" field has the Port Option", it finds that the "Downstream Source Port" field has
value of 1000. Relay2 then uses this port number in the UDP packet the value of 1000. Relay2 then uses this port number in the UDP
when sending the Relay-reply message to Relay1. packet 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 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 agents, as long as the relay agent that uses a non-DHCP UDP port (not
(not 547) and its upstream relay device support this generalized UDP 547) and its upstream relay device support this generalized UDP
source port extension. source port extension.
Similar to the above example, now assume that Relay2 uses the UDP Similar to the above example, but now assume that Relay2 uses the UDP
source port of 2000 instead of 547 as in the diagram. The Relay3 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 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 its "Downstream Source Port" field of the option in the Relay-forward
message. When DHCP server sends the DHCP Relay-reply to Relay3, message. When the DHCP server sends the DHCP Relay-reply to Relay3,
Relay3 finds its own relay option has this "Downstream Source Port" Relay3 finds that its own relay option has this "Downstream Source
with the value of 2000. Relay3 will use this UDP port when sending Port" with the value of 2000. Relay3 will use this UDP port when
the Relay-reply message to Relay2. Relay2 finds its own relay option sending the Relay-reply message to Relay2. Relay2 finds its own
also has this "Downstream Source Port" with the value of 1000. relay option also has this "Downstream Source Port" with the value of
Relay2 will use this UDP port when sending the Relay-reply message to 1000. Relay2 will use this UDP port when sending the Relay-reply
Relay1. message to Relay1.
7. IANA Considerations 7. IANA Considerations
A new sub-option, DHCPv4 Relay Source Port Sub-Option, is defined in IANA has registered "DHCPv4 Relay Source Port Sub-option" (19) for
this document within the IPv4 Relay Agent Information Option. It the IPv4 "Relay Agent Information" option within the "DHCP Relay
needs to be assigned by IANA in the "DHCP Relay Agent Sub-Option Agent Sub-Option Codes" registry <https://www.iana.org/assignments/
Codes" registry, http://www.iana.org/assignments/bootp-dhcp- bootp-dhcp-parameters> [RFC3046].
parameters as specified in [RFC3046].
A new option, DHCPv6 Relay Source Port, is defined in this document IANA has registered "OPTION_RELAY_PORT" (135) for the DHCPv6 "Relay
for DHCPv6 and it needs to be assigned by IANA for the DHCPv6 option Source Port Option" within the DHCPv6 "Option Codes" registry
code, in the "Option Codes" registry for DHCPv6, <http://www.iana.org/assignments/dhcpv6-parameters"> [RFC3315].
http://www.iana.org/assignments/dhcpv6-parameters as specified in
[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 additional security issues.
9. Acknowledgments
The authors would like to thank Peter Arberg, Luyuan Fang, Bhanu
Gopalasetty, Scott Kelly, Andre Kostur, Victor Kuarsingh, Ted Lemon,
Adam Roach, 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
to the definition of The Relay Source Port sub-option and DHCPv6
Relay Source Port Option.
The RFC text was produced using Marshall Rose's xml2rfc tool.
10. Normative References 9. Normative References
[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, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc- DOI 10.17487/RFC2119, March 1997,
editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", [RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997, RFC 2131, DOI 10.17487/RFC2131, March 1997,
<https://www.rfc-editor.org/info/rfc2131>. <https://www.rfc-editor.org/info/rfc2131>.
[RFC3046] Patrick, M., "DHCP Relay Agent Information Option", [RFC3046] Patrick, M., "DHCP Relay Agent Information Option",
RFC 3046, DOI 10.17487/RFC3046, January 2001, RFC 3046, DOI 10.17487/RFC3046, January 2001,
<https://www.rfc-editor.org/info/rfc3046>. <https://www.rfc-editor.org/info/rfc3046>.
[RFC3118] Droms, R., Ed. and W. Arbaugh, Ed., "Authentication for [RFC3118] Droms, R., Ed. and W. Arbaugh, Ed., "Authentication for
DHCP Messages", RFC 3118, DOI 10.17487/RFC3118, June 2001, DHCP Messages", RFC 3118, DOI 10.17487/RFC3118, June 2001,
<https://www.rfc-editor.org/info/rfc3118>. <https://www.rfc-editor.org/info/rfc3118>.
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
2003, <https://www.rfc-editor.org/info/rfc3315>. 2003, <https://www.rfc-editor.org/info/rfc3315>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
Acknowledgments
The authors would like to thank Peter Arberg, Luyuan Fang, Bhanu
Gopalasetty, Scott Kelly, Andre Kostur, Victor Kuarsingh, Ted Lemon,
Adam Roach, 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
to the definition of the "Relay Source Port Sub-option" and DHCPv6
"Relay Source Port Option".
Authors' Addresses Authors' Addresses
Naiming Shen Naiming Shen
Cisco Systems Cisco Systems
560 McCarthy Blvd. 560 McCarthy Blvd.
Milpitas, CA 95035 Milpitas, CA 95035
US United States of America
Email: naiming@cisco.com Email: naiming@cisco.com
Enke Chen Enke Chen
Cisco Systems Cisco Systems
560 McCarthy Blvd. 560 McCarthy Blvd.
Milpitas, CA 95035 Milpitas, CA 95035
US United States of America
Email: enkechen@cisco.com Email: enkechen@cisco.com
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