Generalized UDP Source Port for DHCP Relay
RFC 8357
Internet Engineering Task Force (IETF) N. Shen
Request for Comments: 8357 E. Chen
Category: Standards Track Cisco Systems
ISSN: 2070-1721 March 2018
Generalized UDP Source Port for DHCP Relay
Abstract
This document defines an extension to the DHCP protocols that allows
a relay agent to use any available source port for upstream
communications. The extension also allows inclusion of a DHCP option
that can be used to statelessly route responses back to the
appropriate source port on downstream communications.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
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 (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Shen & Chen Standards Track [Page 1]
RFC 8357 DHCP Relay Source Port March 2018
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 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
4. Relay Source Port Sub-option and Option . . . . . . . . . . . 4
4.1. Source Port Sub-option for DHCPv4 . . . . . . . . . . . . 5
4.2. Relay Source Port Option for DHCPv6 . . . . . . . . . . . 5
5. Relay Agent and Server Behavior . . . . . . . . . . . . . . . 6
5.1. DHCPv4 . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.2. DHCPv6 . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.3. Compatibility . . . . . . . . . . . . . . . . . . . . . . 7
5.4. Deployment Considerations . . . . . . . . . . . . . . . . 7
6. Example of an IPv6-Cascaded Relay . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. Normative References . . . . . . . . . . . . . . . . . . . . 9
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
RFC 2131 [RFC2131] and RFC 3315 [RFC3315] specify the use of UDP as
the transport protocol for DHCP. They also define both the server-
and client-side port numbers. The IPv4 server port is UDP number
(67) and the client port is UDP number (68); for IPv6, the server
port is (547) and the client port is (546).
The fixed UDP port combinations for the DHCP protocol scheme creates
challenges in certain DHCP relay operations. For instance, in a
large-scale DHCP relay implementation on a single-switch node, the
DHCP relay functionality may be partitioned among multiple relay
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
number as currently specified, the transport socket operation of DHCP
packets would need to go through a central entity or process, which
would defeat the purpose of distributing DHCP relay functionality.
In some large-scale deployments, the decision to split the DHCP
functionality into multiple processes on a node may not be purely
based on DHCP relay computational load. Rather, DHCP relay could
just be one of the functions in a multi-process implementation.
Shen & Chen Standards Track [Page 2]
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