Generalized Source UDP Port of DHCP Relay
draft-ietf-dhc-relay-port-00

Networking Working Group                                         N. Shen
Internet-Draft                                                   E. Chen
Intended status: Standards Track                           Cisco Systems
Expires: April 30, 2017                                 October 27, 2016

               Generalized Source UDP Port of DHCP Relay
                      draft-ietf-dhc-relay-port-00

Abstract

   This document extends the DHCP and DHCPv6 protocols for the UDP
   transport from relay agent to server and allows the port to be any
   valid number on the DHCP relay system.

Status of This Memo

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   This Internet-Draft will expire on April 30, 2017.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Changes to DHCP and DHCPv6 Specifications . . . . . . . . . .   3
     2.1.  Changes to DHCP in RFC 2131 . . . . . . . . . . . . . . .   3
     2.2.  Changes to DHCPv6 in RFC 3315 . . . . . . . . . . . . . .   3
   3.  Relay Agent Source Port Sub-option and Option . . . . . . . .   4
     3.1.  DHCP Relay Agent Source Port Sub-option . . . . . . . . .   4
     3.2.  DHCPv6 Relay Agent Source Port Option . . . . . . . . . .   4
   4.  Compatibility . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   6
   8.  Document Change Log . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Changes to draft-ietf-dhc-relay-port-00 . . . . . . . . .   6
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   RFC 2131 [RFC2131] and RFC 3315 [RFC3315] specify the DHCP transport
   protocol as UDP.  They also define both the server side and client
   side port numbers.  The DHCP server port is UDP number (67) and the
   client port is UDP number (68); for DHCPv6 the server port is (546)
   and the client port is (547).

   This fixed client port number of DHCP protocol scheme creates
   problems in certain DHCP relay operations and environments.  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 running under different CPUs.  All those
   DHCP relay processes may share the same IP address of the switch
   node.  If the UDP source port has to be a fixed number, the transport
   socket operation of DHCP packets needs to go through a central
   location or process which defeats the purpose of distributed DHCP
   relay functionality.

   In some of the scalable operational environment, the decision to
   split functionality into multiple processes on a node may not be
   purely based on DHCP relay load.  But DHCP relay is one of the
   functions in the multiple process implementation.

   Although assigning the different source IP/IPv6 address for each DHCP
   relay process can be a solution, it requires operational and network
   management involvement.  It needs to be sure, at least for DHCP, the
   address space among the relay and server is in private IPv4 address
   domain.

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   This document proposes the option to relax the fixed source port
   requirement for the DHCP relay agents.  This extension requires the
   DHCP server or relay agent, in the case of relay chaining [RFC3315],
   to remember the inbound packet's UDP port number along with the IP/
   IPv6 address.  The DHCP server MUST use the UDP port number that the
   incoming relay agent uses instead of blindly setting the DHCP fixed
   port number.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Changes to DHCP and DHCPv6 Specifications

2.1.  Changes to DHCP in RFC 2131

   Section 4.1 of RFC 2131 [RFC2131] asserts that: DHCP uses UDP as its
   transport protocol.  DHCP messages from a 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 client' port (68).

   This specification adds to the above paragraph in the paragraph
   below.

   DHCP messages from a relay agent to a server are sent to the 'DHCP
   server' port (67), and the UDP source port it uses can be any valid
   UDP port available on the relay system, including the DHCP port 67.
   The default is port number 67 if there is no explicit configuration
   for generalized source UDP port extension of DHCP relay.

2.2.  Changes to DHCPv6 in RFC 3315

   Section 5.2 of RFC 3315 [RFC3315] asserts that: Clients listen for
   DHCP messages on UDP port 546.  Servers and relay agents listen for
   DHCP messages on UDP port 547.

   This specification adds to the above paragraph in the paragraph
   below.

   DHCP relay agents can listen for DHCP messages from server or another
   relay agent on any valid UDP port available on the relay system
   including the DHCP UDP port 547.  The default is port 547 if there is
   no explicit configuration for generalized source UDP port extension
   of DHCP relay.

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3.  Relay Agent Source Port Sub-option and Option

   Although the DHCP or DHCPv6 server can implicitly detect a source UDP
   port that is different from the standard DHCP port number when it
   receives an inbound message from relay agents, this sub-option makes
   the request explicit for the server to use a non-DHCP UDP port in the
   reply message.

3.1.  DHCP Relay Agent Source Port Sub-option

   The Relay Agent Source Port sub-option is part of the relay-agent-
   information option for DHCPv4 [RFC3046].  It SHOULD be used by the
   relay agent that uses a non-DHCP UDP port communicating with the DHCP
   server.

   The format of the DHCPv4 Relay Agent Source Port Sub-option is shown
   below:

            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            | SubOpt Code   |      Len      |
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where:

      SubOpt Code:  TBD. 8 bits value, to be assigned by IANA.

      Len:     8 bits value to be set to 0.

   When a DHCP server receives a message from relay agent with this
   Relay Source Port sub-option, it MUST remember the inbound message
   UDP source port from the relay agent and use the same port number for
   the UDP destination port that sends the reply message to the same
   relay agent.

3.2.  DHCPv6 Relay Agent Source Port Option

   The Relay Agent Source Port Option is a new DHCPv6 option.  It SHOULD
   be used by the DHCPv6 relay agent that uses a non-DHCP UDP port
   communicating with the DHCP server and upstream relay agent.

   The format of the DHCPv6 Relay Agent Source Port Option is shown
   below:

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       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Option-Code          |         Option-Len            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         UDP Source Port       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where:

      Option-Code:  TBD. 16 bits value, to be assigned by IANA.

      Option-Len:  16 bits value to be set to 2.

      UDP Source Port:  16 bits value.  To be set by the DHCPv6 relay to
               the UDP source port used for the packet.

   With this Relay Source Port Option in the message, when a DHCPv6
   server replies or a relay agent relays a message towards a downstream
   relay agent, it MUST use the same port number for the UDP destination
   to the previous hop relay agent.

4.  Compatibility

   With this extension of DHCP and DHCPv6 source port generalization,
   the server behavior is compatible with the relay agent that uses the
   DHCP fixed UDP port.  The DHCP server will reflect back the UDP well-
   known port number (67/547) that the client uses when relaying back to
   the relay agent.  It is recommended to upgrade the server side first.

   The implementation is advised to allow the configuration for
   specifying a fixed DHCP relay port number.  This is for the case
   where the DHCP relay agent is upgraded with this extension before the
   server side upgrade.

5.  IANA Considerations

   A new sub-option, DHCP Relay Agent Source Port, is defined in this
   document within the DHCPv4 Relay Agent Information Option.  It needs
   to be assigned by IANA from the DHCP Relay Agent sub-options space
   [RFC3046].

   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
   code.

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6.  Security Considerations

   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.

7.  Acknowledgments

   The authors would like to thank Peter Arberg, Bhanu Gopalasetty,
   Andre Kostur, Ted Lemon, and Kishore Seshadri for their review and
   comments of this document.

   The authors would like to thank Bernie Volz for discussions that lead
   to the definition of The Relay Agent Source Port sub-option and
   DHCPv6 Relay Agent Source Port Option.

   The RFC text was produced using Marshall Rose's xml2rfc tool.

8.  Document Change Log

8.1.  Changes to draft-ietf-dhc-relay-port-00

   o  Posted first version of working group draft in October 2016.

   o  This draft was renamed from draft-shen-dhc-client-port-03.txt.

9.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, DOI 10.17487/RFC2131, March 1997,
              <http://www.rfc-editor.org/info/rfc2131>.

   [RFC3046]  Patrick, M., "DHCP Relay Agent Information Option",
              RFC 3046, DOI 10.17487/RFC3046, January 2001,
              <http://www.rfc-editor.org/info/rfc3046>.

   [RFC3315]  Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
              C., and M. Carney, "Dynamic Host Configuration Protocol
              for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
              2003, <http://www.rfc-editor.org/info/rfc3315>.

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Authors' Addresses

   Naiming Shen
   Cisco Systems
   560 McCarthy Blvd.
   Milpitas, CA  95035
   US

   Email: naiming@cisco.com

   Enke Chen
   Cisco Systems
   560 McCarthy Blvd.
   Milpitas, CA  95035
   US

   Email: enkechen@cisco.com

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