wdiff rfc8357.original rfc8357.txt

Networking Working Group
Internet Engineering Task Force (IETF) N. Shen
Internet-Draft
Request for Comments: 8357 E. Chen
Intended status:
Category: Standards Track Cisco Systems
Expires: June 17,
ISSN: 2070-1721 March 2018 December 14, 2017

Generalized UDP Source Port for DHCP Relay
draft-ietf-dhc-relay-port-10

Abstract

This document proposes defines an extension to the DHCP protocols that allows
a relay agent to use any available source port for upstream
communications, and to include
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

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This Internet-Draft will expire on June 17, 2018.
https://www.rfc-editor.org/info/rfc8357.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 3
3. Changes to DHCP Specifications . . . . . . . . . . . . . . . 3 4
3.1. Additions to DHCPv4 in RFC 2131 . . . . . . . . . . . . . 3 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 . . . . . . . . . . . . 4
4.2. Relay Source Port Option for DHCPv6 . . . . . . . . . . . 5
5. Relay Agent and Server Behavior . . . . . . . . . . . . . . . 5
5.1. DHCPv4 . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.2. DHCPv6 . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.3. Compatibility . . . . . . . . . . . . . . . . . . . . . . 6 7
5.4. Deployment Considerations . . . . . . . . . . . . . . . . 7
6. An IPv6 Cascaded Relay Example . of an IPv6-Cascaded Relay . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. Acknowledgments Normative References . . . . . . . . . . . . . . . . . . . . 9
Acknowledgments . . . . . 9
10. Normative References . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 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
side server-
and client side client-side port numbers. The IPv4 server port is UDP number
(67) and the client port is UDP number (68); for IPv6 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
large-scale DHCP relay implementation on a single switch 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 process, which
would defeat the purpose of distributing DHCP relay functionality.

In some large-scale deployment, deployments, 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 Rather, DHCP relay could
just be one of the functions in a multi-process implementation.

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

This document proposes defines an extension to relax the fixed UDP source port
requirement for the DHCP relay agents. This extension requires a
DHCP server to remember the inbound packet's UDP port number along
with the IPv4/IPv6 address. The DHCP server when When sending back
replies replies, the DHCP
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
cascaded
IPv6-cascaded relay agents [RFC3315], the upstream relay agent needs
to use the "Relay Source Port Option" to record the downstream source
port
port, and it MUST use this recorded port number instead of the fixed
DHCP port number when replaying the reply messages.

1.1.

2. Terminology

2.1. Requirements Language

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

2. Terminology
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

2.2. Definitions

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

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

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

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

Non-DHCP UDP Port: Any valid and non-zero UDP port other than port
67 for DHCPv4 and port 547 for DHCPv6.

3. Changes to DHCP Specifications

3.1. Additions to DHCPv4 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).

Relay agents implementing this specification may be configured
instead to 1) use a source port number other than 67 when relaying
messages toward servers, servers and to 2) receive responses toward clients on
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
to support this extension.

3.2. Additions 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.

Relay agents implementing this specification may be configured
instead to 1) use a source port number other than 547 when relaying
messages toward servers, servers and to 2) receive responses toward clients on
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
to support this extension.

4. Relay Source Port Sub-option and Option

Relay agents do not maintain state. To return a message to its
source, the relay agent must include all the required information in
the Relay-Forward Relay-forward message. When a relay in a sequence of cascaded
relays does not use the standard source port, that source port must
be included along with the source address. This option allows the
relay agent to do so.

4.1. Source Port Sub-option for DHCPv4

The Relay Agent relay agent "Source Port Sub-option" is a new option, and it is
part of the relay-agent-information "Relay Agent Information" option for DHCPv4 [RFC3046].

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

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

Where:

SubOpt Code: SUBOPT_RELAY_PORT. 8 bit 8-bit value, to be assigned by
IANA. 19.

Len: 8 bit 8-bit 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 either 1) a DHCPv6 relay agent that uses a non-DHCP UDP port
(not 547) communicating with the IPv6 server and the upstream relay
agent,
agent or by a 2) an IPv6 relay agent that detects the use of a non-DHCP
UDP port (not 547) 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_RELAY_PORT | Option-Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream Source Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Where:

Option-Code: OPTION_RELAY_RELAY_PORT. 16 bit OPTION_RELAY_PORT. 16-bit value, to be
assigned by IANA. 135.

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

Downstream Source Port: 16 bit 16-bit value. To be set by the IPv6 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 (not 547).

5. Relay Agent and Server Behavior

5.1. DHCPv4

When a relay agent uses a non-DHCP UDP port (not 67) communicating to communicate
with the DHCP server, it MUST include the "Source Port Sub-option" in
Relay-forward messages to indicate that.

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
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 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
server or an upstream IPv6 relay agent. Also Also, when an IPv6 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 the port is no not
being used by a downstream relay agent's non-DHCP UDP port usage, agent, the field Downstream Source Port
field MUST be set to zero.

The IPv6 relay agent MUST include this option in the following three
cases:

1. The local relay agent uses a non-DHCP UDP port (not 547).

2) the

2. The downstream relay agent uses a non-DHCP UDP port (not 547).

3) the

3. The local relay agent and the downstream relay agent both use
non-DHCP UDP ports (not 547).

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 an IPv6 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
Relay-reply message. Additionally, the IPv6 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.

5.4. Deployment Considerations

During deployment, it is advisable the operator and/or user of the new DHCP relay play port
implementation should upgrade the DHCP server first when
possible, before the relay
implementations are deployed. This would ensure that the erroneous
case noted in Section 5.3 is not encountered. If the upstream relay
agent or server does not support this extension, this DHCP relay port
feature needs to be disabled.

When the DHCP relay port implementation is deployed, the default
relay agent behavior should use the DHCP UDP port, and it is
recommended that the configuration is setup be set up to allow for the mode of
operation where a non-DHCP port can be used for the DHCP relay
agents.

Although if

If the network uses a 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 with this extension. The firewall rules need to be modified
only
to match only the DHCP server side of the UDP port number, and number and, if
necessary, IP addresses and other attributes.

6. An IPv6 Cascaded Relay Example of an IPv6-Cascaded Relay

An example of IPv6 cascaded IPv6-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 IPv6 devices support this generalized
UDP source port extension except for Relay3. Relay1 is the only
relay agent device that uses a non-DHCP UDP port (not 547). Relay2
is the upstream device of Relay1.

Both Relay1 and Relay2 include the "Relay Source Port Option" in the
Relay-forward message. Relay1 sets the "Downstream Source Port"
field in the option to zero. Relay2 notices that 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" Option", and it sets the
"Downstream Source Port" field in the option to 1000. The IPv6
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 that 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 IPv6 port 547 in the
packet sending the Relay-reply message to its downstream relay agent
or uses UDP port 546 to an IPv6 client.

This DHCP extension works with any combination of IPv6 cascaded IPv6-cascaded relay
agents, as long as the relay agent which that uses a non-DHCP UDP port (not
547) and its upstream relay device support this generalized UDP
source port extension.

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
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
message. When the DHCP server sends the DHCP Relay-reply to Relay3,
Relay3 finds that its own relay option has this "Downstream Source
Port" with the value of 2000. Relay3 will use this UDP port when
sending the Relay-reply message to Relay2. Relay2 finds its own
relay option also has this "Downstream Source Port" with the value of
1000. Relay2 will use this UDP port when sending the Relay-reply
message to Relay1.

7. IANA Considerations

A new sub-option, DHCPv4

IANA has registered "DHCPv4 Relay Source Port Sub-Option, is defined in
this document within Sub-option" (19) for
the IPv4 Relay "Relay Agent Information Option. It
needs to be assigned by IANA in Information" option within the "DHCP Relay
Agent Sub-Option Codes" registry, http://www.iana.org/assignments/bootp-dhcp-
parameters as specified in registry <https://www.iana.org/assignments/
bootp-dhcp-parameters> [RFC3046].

A new option, DHCPv6 Relay Source Port, is defined in this document
for DHCPv6 and it needs to be assigned by

IANA has registered "OPTION_RELAY_PORT" (135) for the DHCPv6 option
code, in "Relay
Source Port Option" within the DHCPv6 "Option Codes" registry for DHCPv6,
http://www.iana.org/assignments/dhcpv6-parameters as specified in
<http://www.iana.org/assignments/dhcpv6-parameters"> [RFC3315].

8. Security Considerations

[RFC3118] and [RFC3315] described many of the threats in using DHCP.
This extension does not raise addition 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

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

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

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

[RFC3118] Droms, R., Ed. and W. Arbaugh, Ed., "Authentication for
DHCP Messages", RFC 3118, DOI 10.17487/RFC3118, June 2001,
<https://www.rfc-editor.org/info/rfc3118>.

[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, <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

Naiming Shen
Cisco Systems
560 McCarthy Blvd.
Milpitas, CA 95035
US
United States of America

Email: naiming@cisco.com

Enke Chen
Cisco Systems
560 McCarthy Blvd.
Milpitas, CA 95035
US
United of States of America

Email: enkechen@cisco.com