draft-ietf-dhc-relay-port-01.txt   draft-ietf-dhc-relay-port-02.txt 
Networking Working Group N. Shen Networking Working Group N. Shen
Internet-Draft E. Chen Internet-Draft E. Chen
Intended status: Standards Track Cisco Systems Intended status: Standards Track Cisco Systems
Expires: July 9, 2017 January 5, 2017 Expires: September 1, 2017 February 28, 2017
Generalized Source UDP Port of DHCP Relay Generalized UDP Source Port for DHCP Relay
draft-ietf-dhc-relay-port-01 draft-ietf-dhc-relay-port-02
Abstract Abstract
This document extends the DHCP and DHCPv6 protocols for the UDP This document proposes an extension to the DHCP and DHCPv6 protocols
transport from relay agent to server and allows the port to be any that allows any valid number to be used as the relay agent UDP source
valid number on the DHCP relay system. port for DHCP packets.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on July 9, 2017. This Internet-Draft will expire on September 1, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Changes to DHCP and DHCPv6 Specifications . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Changes to DHCP in RFC 2131 . . . . . . . . . . . . . . . 3 3. Changes to DHCP and DHCPv6 Specifications . . . . . . . . . . 3
2.2. Changes to DHCPv6 in RFC 3315 . . . . . . . . . . . . . . 3 3.1. Changes to DHCP in RFC 2131 . . . . . . . . . . . . . . . 3
3. Relay Agent Source Port Sub-option and Option . . . . . . . . 4 3.2. Changes to DHCPv6 in RFC 3315 . . . . . . . . . . . . . . 4
3.1. DHCP Relay Agent Source Port Sub-option . . . . . . . . . 4 4. Relay Source Port Sub-option and Option . . . . . . . . . . . 4
3.2. DHCPv6 Relay Agent Source Port Option . . . . . . . . . . 4 4.1. Source Port Sub-option for DHCPv4 . . . . . . . . . . . . 4
4. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 6 4.2. Relay Source Port Option for DHCPv6 . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 5. A DHCPv6 Cascaded Relay Example . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 6. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. Document Change Log . . . . . . . . . . . . . . . . . . . . . 7 8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8.1. Changes to draft-ietf-dhc-relay-port-01 . . . . . . . . . 7 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
8.2. Changes to draft-ietf-dhc-relay-port-00 . . . . . . . . . 7 10. Document Change Log . . . . . . . . . . . . . . . . . . . . . 8
9. Normative References . . . . . . . . . . . . . . . . . . . . 7 10.1. Changes to draft-ietf-dhc-relay-port-02 . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 10.2. Changes to draft-ietf-dhc-relay-port-01 . . . . . . . . 9
10.3. Changes to draft-ietf-dhc-relay-port-00 . . . . . . . . 9
11. Normative References . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction 1. Introduction
RFC 2131 [RFC2131] and RFC 3315 [RFC3315] specify the DHCP transport RFC 2131 [RFC2131] and RFC 3315 [RFC3315] specify the use of UDP as
protocol as UDP. They also define both the server side and client the transport protocol for DHCP and DHCPv6. They also define both
side port numbers. The DHCP server port is UDP number (67) and the the server side and client side port numbers. The DHCP server port
client port is UDP number (68); for DHCPv6 the server port is (546) is UDP number (67) and the client port is UDP number (68); for DHCPv6
and the client port is (547). the server port is (546) and the client port is (547).
This fixed port number of DHCP protocol scheme creates problems in This fixed UDP port of DHCP protocol scheme creates challenges in
certain DHCP relay operations and environments. For instance, in a certain DHCP relay operations. For instance, in a large scale DHCP
large scale DHCP relay implementation on a single switch node, the relay implementation on a single switch node, the DHCP relay
DHCP relay functionality may be partitioned among multiple relay functionality may be partitioned among multiple relay processes. All
processes running under different CPUs. All those DHCP relay these DHCP relay processes may share the same IP address of the
processes may share the same IP address of the switch node. If the switch node. If the UDP source port has to be a fixed number as
UDP source port has to be a fixed number, the transport socket currently specified, the transport socket operation of DHCP packets
operation of DHCP packets needs to go through a central location or would need to go through a central entity or process which would
process which defeats the purpose of distributed DHCP relay defeat the purpose of distributing DHCP relay functionality.
functionality.
In some of the scalable operational environment, the decision to In some large-scale deployment, the decision to split the DHCP
split functionality into multiple processes on a node may not be functionality into multiple processes on a node may not be purely
purely based on DHCP relay load. But DHCP relay is one of the based on DHCP relay computational load. But rather DHCP relay could
functions in the multiple process implementation. just be one of the functions in a multi-process implementation.
Although assigning the different source IP/IPv6 address for each DHCP Although assigning a different IP/IPv6 source address for each DHCP
relay process can be a solution, it requires operational and network relay process can be a solution, it would introduce operational and
management involvement. It needs to be sure, at least for DHCP, the network management complexities, especially given the scarceness of
address space among the relay and server is in private IPv4 address the IPv4 addresses.
domain.
This document proposes the option to relax the fixed source port This document proposes an extension to relax the fixed UDP source
requirement for the DHCP relay agents. This extension requires the port requirement for the DHCP relay agents. This extension requires
DHCP server or relay agent, in the case of relay chaining [RFC3315], a DHCP server or relay agent, in the case of cascaded relay agents
to remember the inbound packet's UDP port number along with the IP/ [RFC3315], to remember the inbound packet's UDP port number along
IPv6 address. The DHCP server when sending back replies MUST use the with the IP/IPv6 address. The DHCP server when sending back replies
UDP port number that the incoming relay agent uses instead of blindly MUST use the UDP port number that the incoming relay agent uses
setting the DHCP fixed port number. instead of the fixed DHCP port number.
1.1. Requirements Language 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
2. Changes to DHCP and DHCPv6 Specifications 2. Terminology
2.1. Changes to DHCP in RFC 2131 Downstream Device: In the DHCP relay context, it refers to the next
relay agent for forwarding Relay-reply Messages.
Section 4.1 of RFC 2131 [RFC2131] asserts that: DHCP uses UDP as its Upstream Device: In the DHCP relay context, it refers to the next
transport protocol. DHCP messages from a client to a server are sent relay agent or DHCP server for forwarding Relay-forward
to the 'DHCP server' port (67), and DHCP messages from a server to a Messages.
client are sent to the 'DHCP client' port (68).
This specification adds to the above paragraph in the paragraph Relay Source Port: This is the UDP port that a relay agent uses to
below. receive Relay-forward Messages from an upstream device.
DHCP messages from a relay agent to a server are sent to the 'DHCP Downstream Source Port: This is the UDP port that the downstream
server' port (67), and the UDP source port it uses can be any valid device uses when forwarding Relay-forward Messages to this
UDP port available on the relay system, including the DHCP port 67. relay agent device. This UDP port is to be used by this
The default is port number 67 if there is no explicit configuration relay agent device when forwarding the Relay-reply Messages
for generalized source UDP port extension of DHCP relay. to that downstream device.
2.2. Changes to DHCPv6 in RFC 3315 Non-DHCP UDP Port: Any valid UDP port other than port 67 for DHCP
and port 547 for DHCPv6.
Section 5.2 of RFC 3315 [RFC3315] asserts that: Clients listen for 3. Changes to DHCP and DHCPv6 Specifications
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 3.1. Changes to DHCP in RFC 2131
below.
DHCP relay agents can listen for DHCP messages from server or another Section 4.1 of RFC 2131 [RFC2131] specifies that:
upstream 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.
3. Relay Agent Source Port Sub-option and Option 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).
Although the DHCP or DHCPv6 server can implicitly detect a source UDP This specification adds the following extension to the above
port that is different from the standard DHCP port number when it paragraph.
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 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.
The Relay Agent Source Port sub-option is part of the relay-agent- 3.2. Changes to DHCPv6 in RFC 3315
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 Section 5.2 of RFC 3315 [RFC3315] specifies that:
below:
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 is port 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 a UDP
source port when it receives an inbound 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.
4.1. Source Port Sub-option for DHCPv4
The Relay Agent "Source Port Sub-option" is a new option, and it is
part of the relay-agent-information option for DHCPv4 [RFC3046]. It
SHOULD be used by a relay agent that uses a non-DHCP UDP port
communicating with the DHCP server.
The format of the "Source Port Sub-option" is shown below:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SubOpt Code | Len | | SubOpt Code | Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where: Where:
SubOpt Code: TBD. 8 bits value, to be assigned by IANA. SubOpt Code: SUBOPT_RELAY_PORT. 8 bits value, to be assigned by
IANA.
Len: 8 bits value to be set to 0. Len: 8 bits value to be set to 0.
When a DHCP server receives a message from relay agent with this When a DHCP server receives a message from a relay agent with the
Relay Source Port sub-option, it MUST remember the inbound message "Source Port Sub-option", it MUST remember the UDP source port of the
UDP source port from the relay agent and use the same port number for message and use that port number as the UDP destination port when
the UDP destination port that sends the reply message to the same sending the reply message to the same relay agent.
relay agent.
3.2. DHCPv6 Relay Agent Source Port Option 4.2. Relay Source Port Option for DHCPv6
The Relay Agent Source Port Option is a new DHCPv6 option. It SHOULD The "Relay Source Port Option" is a new DHCPv6 option. It SHOULD be
be used either by a DHCPv6 relay agent that uses a non-DHCP UDP port 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 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 DHCPv6 relay agent that detects the use of a non-DHCP UDP port
by a downstream relay agent. by a downstream relay agent.
The format of the DHCPv6 Relay Agent Source Port Option is shown The format of the "Relay Source Port Option" is shown below:
below:
0 1 2 3 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 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 | | OPTION_RELAY_RELAY_PORT | Option-Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream UDP Source Port | | Downstream Source Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where: Where:
Option-Code: TBD. 16 bits value, to be assigned by IANA. Option-Code: OPTION_RELAY_RELAY_PORT. 16 bits value, to be
assigned by IANA.
Option-Len: 16 bits value to be set to 2. Option-Len: 16 bits value to be set to 2.
Downstream UDP Source Port: 16 bits value. To be set by the Downstream Source Port: 16 bits value. To be set by the DHCPv6
DHCPv6 relay to the downstream relay agent's UDP source relay either to the downstream relay agent's UDP source
port used for the UDP packet or to be set to zero. port used for the UDP packet, or to zero if only the
local relay agent uses the non-DHCP UDP port.
The DHCPv6 relay agent SHOULD include this Relay Source Port Option The DHCPv6 relay agent SHOULD include the "Relay Source Port Option"
when it uses a non-DHCP UDP port to communicate to the DHCPv6 server when it uses a non-DHCP UDP port to communicate to a DHCPv6 server or
or an upstream DHCPv6 relay agent. Also when a DHCPv6 relay agent an upstream DHCPv6 relay agent. Also when a DHCPv6 relay agent
detects that the downstream relay agent uses a non-DHCP UDP port in detects that a downstream relay agent uses a non-DHCP UDP port in the
the packet, it MUST record the port number in the Downstream UDP packet, it MUST record the port number in the "Downstream Source
Source Port field of this option. If this option is included to Port" field of this option. If this option is included to indicate
indicate only the local non-DHCP UDP port usage and there is no only the local non-DHCP UDP port usage and there is no downstream
downstream relay agent's non-DHCP UDP port usage, the field relay agent's non-DHCP UDP port usage, the field Downstream Source
Downstream UDP Source Port MUST be set to zero. Port field MUST be set to zero.
When a DHCPv6 server receives the relayed DHCPv6 packet with this The DHCPv6 relay agent SHOULD include this option in the following
Relay Source Port Option, it MUST copy and add the option when three cases:
constructing the Relay-Reply chain in response to the Relay-Forward
messages. This option MUST NOT appear in any message except a Relay-
Forward or Relay-Reply message.
With this Relay Source Port Option in the message, when a DHCPv6 1) The local relay agent uses a non-DHCP UDP port.
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 message by the relay agent.
When a relay agent receives this Relay-Reply message with this option 2) the downstream relay agent uses a non-DHCP UDP port.
from the server or from an upstream relay agent, and if the
Downstream UDP Source Port value is non-zero, it MUST use this UDP
port to relay the Relay-Reply message to the downstream relay agent.
4. Compatibility 3) the local relay agent and the downstream relay agent both use
non-DHCP UDP ports.
With this extension of DHCP and DHCPv6 source port generalization, In the first case, the value of the field in "Downstream Source Port"
the server behavior is compatible with the relay agent that uses the field is set to zero. In the other two cases, the value of the field
DHCP fixed UDP port. The DHCP server will reflect back the UDP well- is set to the UDP port number that the downstream relay agent uses.
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 relay agent configuration When a DHCPv6 server receives a Relay-forward message with the "Relay
for specifying a fixed DHCP relay port number. This is for the case Source Port Option", it MUST copy the option when constructing the
where the DHCP relay agent is upgraded with this extension before the Relay-reply chain in response to the Relay-forward message. This
server side upgrade. option MUST NOT appear in any message other than a Relay-forward or
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.
5. IANA Considerations 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.
A new sub-option, DHCP Relay Agent Source Port, is defined in this 5. A DHCPv6 Cascaded Relay Example
document within the DHCPv4 Relay Agent Information Option. It needs
to be assigned by IANA from the DHCP Relay Agent sub-options space 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
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 for DHCP and DHCPv6, the server
behavior is compatible with the relay agent that uses the normal DHCP
UDP port. The DHCP server will use the well-known UDP port (67 or
547) when sending Relay-reply message back to the relay agent. It is
recommended to upgrade the server side first before using a non-DHCP
UDP port for a 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.
7. IANA Considerations
A new sub-option, DHCP Relay 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]. [RFC3046].
A new option, DHCPv6 Relay Source Port, is defined in this document 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 for DHCPv6 and it needs to be assigned by IANA for the DHCPv6 option
code. code.
6. Security Considerations 8. Security Considerations
If the network uses firewall to block or allow DHCP packets with both If the network uses firewall to block or allow DHCP packets with both
static UDP source and destination port numbers, this may no longer static UDP source and destination port numbers, this may no longer
match the packets from new DHCP relay agent and server software. The 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 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 of the UDP port number, and if necessary, IP addresses and other
attributes. attributes.
7. Acknowledgments 9. Acknowledgments
The authors would like to thank Peter Arberg, Bhanu Gopalasetty, The authors would like to thank Peter Arberg, Bhanu Gopalasetty,
Andre Kostur, Ted Lemon, and Kishore Seshadri for their review and Andre Kostur, Ted Lemon, and Kishore Seshadri for their review and
comments of this document. comments of this document.
The authors would like to thank Bernie Volz for discussions that lead The authors would like to thank Bernie Volz for discussions that lead
to the definition of The Relay Agent Source Port sub-option and to the definition of The Relay Source Port sub-option and DHCPv6
DHCPv6 Relay Agent Source Port Option. Relay Source Port Option.
The RFC text was produced using Marshall Rose's xml2rfc tool. The RFC text was produced using Marshall Rose's xml2rfc tool.
8. Document Change Log 10. Document Change Log
8.1. Changes to draft-ietf-dhc-relay-port-01 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 Posted the draft in January 2017.
o Change the DHCPv6 Relay Agent Source Port Option, UDP Source Port o Change the DHCPv6 Relay Source Port Option, UDP Source Port field
field to Downstream UDP Source Port. Add the option handling to Downstream Source Port. Add the option handling mechanism for
mechanism for DHCPv6 server and relay agents. DHCPv6 server and relay agents.
8.2. Changes to draft-ietf-dhc-relay-port-00 10.3. Changes to draft-ietf-dhc-relay-port-00
o Posted first version of working group draft in October 2016. o Posted first version of working group draft in October 2016.
o This draft was renamed from draft-shen-dhc-client-port-03.txt. o This draft was renamed from draft-shen-dhc-client-port-03.txt.
9. Normative References 11. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", [RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997, RFC 2131, DOI 10.17487/RFC2131, March 1997,
<http://www.rfc-editor.org/info/rfc2131>. <http://www.rfc-editor.org/info/rfc2131>.
 End of changes. 50 change blocks. 
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