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Versions: (draft-shen-dhc-client-port) 00 01 02 03 04 05 06 07 08 09 10 RFC 8357

Networking Working Group                                         N. Shen
Internet-Draft                                                   E. Chen
Intended status: Standards Track                           Cisco Systems
Expires: October 20, 2017                                 April 18, 2017


               Generalized UDP Source Port for DHCP Relay
                      draft-ietf-dhc-relay-port-04

Abstract

   This document proposes an extension to the DHCP and DHCPv6 protocols
   that allows any valid number to be used as the relay agent's UDP
   source port for DHCP packets.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   This Internet-Draft will expire on October 20, 2017.

Copyright Notice

   Copyright (c) 2017 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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   described in the Simplified BSD License.





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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Changes to DHCP and DHCPv6 Specifications . . . . . . . . . .   3
     3.1.  Changes to DHCP in RFC 2131 . . . . . . . . . . . . . . .   4
     3.2.  Changes to DHCPv6 in RFC 3315 . . . . . . . . . . . . . .   4
   4.  Relay Source Port Sub-option and Option . . . . . . . . . . .   4
     4.1.  Source Port Sub-option for DHCP . . . . . . . . . . . . .   5
     4.2.  Relay Source Port Option for DHCPv6 . . . . . . . . . . .   5
   5.  Relay Agent and Server Behavior . . . . . . . . . . . . . . .   6
     5.1.  DHCP  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.2.  DHCPv6  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.3.  Compatibility . . . . . . . . . . . . . . . . . . . . . .   7
   6.  A DHCPv6 Cascaded Relay Example . . . . . . . . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   10. Document Change Log . . . . . . . . . . . . . . . . . . . . .   9
     10.1.  Changes to draft-ietf-dhc-relay-port-04  . . . . . . . .   9
     10.2.  Changes to draft-ietf-dhc-relay-port-03  . . . . . . . .   9
     10.3.  Changes to draft-ietf-dhc-relay-port-02  . . . . . . . .   9
     10.4.  Changes to draft-ietf-dhc-relay-port-01  . . . . . . . .   9
     10.5.  Changes to draft-ietf-dhc-relay-port-00  . . . . . . . .   9
   11. Normative References  . . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   RFC 2131 [RFC2131] and RFC 3315 [RFC3315] specify the use of UDP as
   the transport protocol for DHCP and DHCPv6.  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 UDP port of 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
   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 deployment, the decision to split the DHCP
   functionality into multiple processes on a node may not be purely



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   based on DHCP relay computational load.  But rather DHCP relay could
   just be one of the functions in a multi-process implementation.

   Although assigning a different IP/IPv6 source address for each DHCP
   relay process can be a solution, it would introduce operational and
   network management complexities, especially given the scarceness of
   the IPv4 addresses.

   This document proposes an extension to relax the fixed UDP source
   port requirement for the DHCP relay agents.  This extension requires
   a DHCP server or relay agent, in the case of cascaded relay agents
   [RFC3315], to remember the inbound packet's UDP port number along
   with the IP/IPv6 address.  The DHCP server when sending back replies
   MUST use the UDP port number that the incoming relay agent uses
   instead of the fixed DHCP 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.  Terminology

   Downstream Device:  In the DHCP relay context, it refers to the next
            relay agent for forwarding Relay-reply Messages.

   Upstream Device:  In the DHCP relay context, it refers to the next
            relay agent or DHCP server for forwarding Relay-forward
            Messages.

   Relay Source Port:  This is the UDP port that a relay agent uses to
            receive Relay-forward Messages from an upstream device.

   Downstream Source Port:  This is the UDP port that the downstream
            device uses when forwarding Relay-forward Messages to this
            relay agent device.  This UDP port is to be used by this
            relay agent device when forwarding the Relay-reply Messages
            to that downstream device.

   Non-DHCP UDP Port:  Any valid UDP port other than port 67 for DHCP
            and port 547 for DHCPv6.

3.  Changes to DHCP and DHCPv6 Specifications







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3.1.  Changes to DHCP in RFC 2131

   Section 4.1 of RFC 2131 [RFC2131] specifies 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 the following extension to the above
   paragraph.

      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 in the relay system, including the DHCP
      port 67.  The default port number is 67 if there is no explicit
      configuration for the generalized source UDP port extension for
      DHCP relay.

3.2.  Changes to DHCPv6 in RFC 3315

   Section 5.2 of RFC 3315 [RFC3315] specifies 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 the following extension to the above
   paragraph.

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

4.  Relay Source Port Sub-option and Option

   Although a DHCP or DHCPv6 server can implicitly determine the UDP
   source port when it receives a message from a relay agent, this sub-
   option makes the request explicit for the server to use a non-DHCP
   UDP port in the reply message.  When DHCPv6 cascaded relay agents are
   involved, the downstream non-DHCP UDP port needs to be recorded using
   the option.








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4.1.  Source Port Sub-option for DHCP

   The Relay Agent "Source Port Sub-option" is a new option, and it is
   part of the relay-agent-information option for DHCP [RFC3046].

   The format of the "Source Port Sub-option" is shown below:

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

   Where:



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

      Len:     8 bits value to be set to 0.

4.2.  Relay Source Port Option for DHCPv6

   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
   communicating with the DHCP server and the upstream relay agent, or
   by a DHCPv6 relay agent that detects the use of a non-DHCP UDP port
   by a downstream relay agent.

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

       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_RELAY_RELAY_PORT    |         Option-Len            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Downstream Source Port     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where:



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

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





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      Downstream Source Port:  16 bits value.  To be set by the DHCPv6
               relay either to the downstream relay agent's UDP source
               port used for the UDP packet, or to zero if only the
               local relay agent uses the non-DHCP UDP port.

5.  Relay Agent and Server Behavior

5.1.  DHCP

   When a relay agent uses a non-DHCP UDP port communicating with the
   DHCP server, it MUST include the "Source Port Sub-option" in Relay-
   forward messages to indicate that.

   When a DHCP server receives a message from a relay agent with 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
   sending the reply message to the same relay agent.

5.2.  DHCPv6

   The DHCPv6 relay agent MUST include the "Relay Source Port Option"
   when it uses a non-DHCP UDP port to communicate to a DHCPv6 server or
   an upstream DHCPv6 relay agent.  Also when a DHCPv6 relay 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 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 downstream
   relay agent's non-DHCP UDP port usage, the field Downstream Source
   Port field MUST be set to zero.

   The DHCPv6 relay agent MUST include this option in the following
   three cases:

      1) The local relay agent uses a non-DHCP UDP port.

      2) the downstream relay agent uses a non-DHCP UDP port.

      3) the local relay agent and the downstream relay agent both use
      non-DHCP UDP ports.

   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
   to the UDP port number that the downstream relay agent uses.

   When a DHCPv6 server receives a Relay-forward message with the "Relay
   Source Port Option", it MUST copy the option when constructing the
   Relay-reply chain in response to the Relay-forward message.  This
   option MUST NOT appear in any message other than a Relay-forward or



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   Relay-reply message.  Additionally, the DHCPv6 server MUST check and
   use the UDP source port from the UDP packet of the Relay-forward
   message in replying to the relay agent.

   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
   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
   downstream relay agent.

5.3.  Compatibility

   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
   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
   communicate to the relay agent.

   The implementation is advised to allow configuration for relay agent
   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.

6.  A DHCPv6 Cascaded Relay Example

   An example of DHCPv6 cascaded relay agents with the "Relay Source
   Port Option" is shown below.




              (forward)          (forward)          (forward)
      Relay1 ----------> Relay2 ----------> Relay3 ----------> Server
          (1000)              (547)              (547)
               (reply)            (reply)            (reply)
             <----------        <----------        <----------


   In the above diagram, all the DHCPv6 devices support this generalized
   UDP source port extension except for Relay3.  Relay1 is the only
   relay agent device uses a non-DHCP UDP port.  Relay2 is the upstream
   device of Relay1.

   Both Relay1 and Relay2 include the "Relay Source Port Option" in
   Relay-forward message.  Relay1 sets the "Downstream Source Port"
   field in the option to zero.  Relay2 notices the "Relay Source Port
   Option" is included in the message from Relay1, and it determines
   that the UDP source port used by Relay1 is 1000.  Relay2 will include
   the "Relay Source Port Option" and it sets the "Downstream Source



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   Port" field in the option to 1000.  The DHCPv6 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
   Port Option", it finds the "Downstream Source Port" field has the
   value of 1000.  Relay2 then uses this port number in the UDP packet
   when sending the Relay-reply message to Relay1.

   When Relay1 receives the Relay-reply message with the "Relay Source
   Port Option", it finds that the "Downstream Source Port" field has
   the value of zero.  Relay1 then uses the normal DHCP port 547 in the
   packet sending the Relay-reply message to its downstream relay agent
   or uses UDP port 546 to a DHCPv6 client.

7.  IANA Considerations

   A new sub-option, DHCP Relay Source Port, is defined in this document
   within the DHCP 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.

8.  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.

9.  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 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.





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10.  Document Change Log

10.1.  Changes to draft-ietf-dhc-relay-port-04

   o  Posted the draft in April 2017.

   o  Rephrased the relay agent and server requirement with this relay
      port feature.

10.2.  Changes to draft-ietf-dhc-relay-port-03

   o  Posted the draft in April 2017.

   o  Added the "Relay Agent and Server Behavior" section.

10.3.  Changes to draft-ietf-dhc-relay-port-02

   o  Posted the draft in February 2017.

   o  Added the Terminology section.

   o  Defined the Sub-option and Option names for DHCP and DHCPv6.

   o  Added the DHCPv6 cascaded relay agents example.

10.4.  Changes to draft-ietf-dhc-relay-port-01

   o  Posted the draft in January 2017.

   o  Change the DHCPv6 Relay Source Port Option, UDP Source Port field
      to Downstream Source Port.  Add the option handling mechanism for
      DHCPv6 server and relay agents.

10.5.  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.

11.  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>.






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   [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>.

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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