wdiff draft-ietf-dhc-relay-port-01.txt draft-ietf-dhc-relay-port-02.txt

Networking Working Group N. Shen
Internet-Draft E. Chen
Intended status: Standards Track Cisco Systems
Expires: July 9, September 1, 2017 January 5, February 28, 2017

Generalized Source UDP Source Port of for DHCP Relay
draft-ietf-dhc-relay-port-01
draft-ietf-dhc-relay-port-02

Abstract

This document extends proposes an extension to the DHCP and DHCPv6 protocols for the UDP
transport from relay agent to server and
that allows the port to be any valid number on to be used as the DHCP relay system. agent UDP source
port for DHCP packets.

Status of This Memo

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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
2.1.
3.1. Changes to DHCP in RFC 2131 . . . . . . . . . . . . . . . 3
2.2.
3.2. Changes to DHCPv6 in RFC 3315 . . . . . . . . . . . . . . 3
3. 4
4. Relay Agent Source Port Sub-option and Option . . . . . . . . . . . 4
3.1. DHCP Relay Agent
4.1. Source Port Sub-option for DHCPv4 . . . . . . . . . . . . 4
3.2. DHCPv6
4.2. Relay Agent Source Port Option for DHCPv6 . . . . . . . . . . 4
4. . 5
5. A DHCPv6 Cascaded Relay Example . . . . . . . . . . . . . . . 6
6. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 6
5. 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. 8
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
8. 8
10. Document Change Log . . . . . . . . . . . . . . . . . . . . . 7
8.1. 8
10.1. Changes to draft-ietf-dhc-relay-port-01 draft-ietf-dhc-relay-port-02 . . . . . . . . 8
10.2. Changes to draft-ietf-dhc-relay-port-01 . 7
8.2. . . . . . . . 9
10.3. Changes to draft-ietf-dhc-relay-port-00 . . . . . . . . . 7
9. 9
11. Normative References . . . . . . . . . . . . . . . . . . . . 7 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 9

1. Introduction

RFC 2131 [RFC2131] and RFC 3315 [RFC3315] specify the DHCP use of UDP as
the transport protocol as UDP. 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 number of DHCP protocol scheme creates problems challenges in
certain DHCP relay operations and environments. 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 running under different CPUs. processes. All those
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, number as
currently specified, the transport socket operation of DHCP packets needs
would need to go through a central location entity or process which defeats would
defeat the purpose of distributed distributing DHCP relay functionality.

In some of the scalable operational environment, large-scale deployment, the decision to split the DHCP
functionality into multiple processes on a node may not be purely
based on DHCP relay computational load. But rather DHCP relay is could
just be one of the functions in the multiple process a multi-process implementation.

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

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

Downstream Device: In the DHCP and DHCPv6 Specifications

2.1. Changes relay context, it refers to the next
relay agent for forwarding Relay-reply Messages.

Upstream Device: In the DHCP in RFC 2131

Section 4.1 of RFC 2131 [RFC2131] asserts that: relay context, it refers to the next
relay agent or DHCP uses UDP as 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

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

2.2.

3.2. Changes to DHCPv6 in RFC 3315

Section 5.2 of RFC 3315 [RFC3315] asserts 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 in the paragraph
below.
paragraph.

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

4. Relay Agent Source Port Sub-option and Option

Although the a DHCP or DHCPv6 server can implicitly detect determine a source UDP
source port that is different from the standard DHCP port number when it receives an inbound message from a relay agents, agent,
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 When DHCPv6 cascaded relay
agents are involved, the downstream non-DHCP UDP port needs to be
recorded using the option.

4.1. Source Port Sub-option for DHCPv4

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

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

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

Where:

SubOpt Code: TBD. SUBOPT_RELAY_PORT. 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 a relay agent with this
Relay Source the
"Source Port sub-option, Sub-option", it MUST remember the inbound message UDP source port from of the relay agent
message and use the same that port number for as the UDP destination port that sends when
sending the reply message to the same relay agent.

3.2. DHCPv6

4.2. Relay Agent Source Port Option for DHCPv6

The Relay Agent "Relay Source Port Option Option" is a new DHCPv6 option. It SHOULD 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 DHCPv6 Relay Agent "Relay Source Port Option 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-Code OPTION_RELAY_RELAY_PORT | Option-Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream UDP Source Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Where:

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

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

Downstream UDP 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 packet, or to be set to zero. zero if only the
local relay agent uses the non-DHCP UDP port.

The DHCPv6 relay agent SHOULD include this Relay the "Relay Source Port Option Option"
when it uses a non-DHCP UDP port to communicate to the a DHCPv6 server or
an upstream DHCPv6 relay agent. Also when a DHCPv6 relay agent
detects that the a downstream relay agent uses a non-DHCP UDP port in the
packet, it MUST record the port number in the Downstream UDP "Downstream Source Port
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 UDP Source
Port field MUST be set to zero.

When a DHCPv6 server receives the relayed

The DHCPv6 packet with relay agent SHOULD include this
Relay Source 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 field in "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, Option", it MUST copy and add the option when constructing the Relay-Reply
Relay-reply chain in response to the Relay-Forward
messages. Relay-forward message. This
option MUST NOT appear in any message except other than a Relay-
Forward Relay-forward or Relay-Reply
Relay-reply message.

With this Relay Source Port Option in Additionally, the message, when a DHCPv6 server replies the Relay-Reply message towards a relay agent, it MUST check and
use the UDP source port from the UDP packet of the Relay-
Forward Relay-forward
message by in replying to the relay agent.

When a relay agent receives this Relay-Reply a Relay-reply message with this option
from the "Relay
Source Port Option" from a server or from an upstream relay agent, and if
the
Downstream UDP "Downstream Source Port value Port" field in the option is non-zero, it MUST
use this UDP port number to relay forward the Relay-Reply Relay-reply message to the
downstream relay agent.

4. Compatibility

With

5. 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 DHCP 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
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.

6. Compatibility

With this source port generalization, generalization for DHCP and DHCPv6, the server
behavior is compatible with the relay agent that uses the normal DHCP fixed
UDP port. The DHCP server will reflect back use the well-known UDP well-
known port number (67/547) that the client uses (67 or
547) when relaying sending Relay-reply message back to the relay agent. It is
recommended to upgrade the server side first. first before using a non-DHCP
UDP port for a relay agent.

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

5. either using a normal DHCP UDP port or non-DHCP UDP port.

7. 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.

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 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.

10. Document Change Log

8.1.

10.1. 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 DHCPv4 and DHCPv6.

o Added the DHCPv6 cascaded relay agents example.

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

o Posted the draft in January 2017.

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

8.2.

10.3. 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>.

[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