Network Working Group Q. Sun
Internet-Draft Y. Cui
Intended status: Standards Track Tsinghua University
Expires: October 05, 2013 M. Siodelski
ISC
S. Krishnan
Ericsson
I. Farrer
Deutsche Telekom AG
April 03, 2013
DHCPv4 over DHCPv6 Transport
draft-scskf-dhc-dhcpv4-over-dhcpv6-01
Abstract
This document describes a mechanism for obtaining IPv4 parameters in
IPv6 networks by carrying DHCPv4 messages over DHCPv6 transport.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
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This Internet-Draft will expire on October 05, 2013.
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 2
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
4. Architecture Overview . . . . . . . . . . . . . . . . . . . . 3
5. BOOTP Message Option Format . . . . . . . . . . . . . . . . . 4
6. Client Behavior . . . . . . . . . . . . . . . . . . . . . . . 5
7. Relay Agent Behavior . . . . . . . . . . . . . . . . . . . . 5
8. Server Behavior . . . . . . . . . . . . . . . . . . . . . . . 6
9. Security Considerations . . . . . . . . . . . . . . . . . . . 6
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
11. Contributors List . . . . . . . . . . . . . . . . . . . . . . 6
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
12.1. Normative References . . . . . . . . . . . . . . . . . . 7
12.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
As the migration towards IPv6 continues, IPv6 only networks will
become more prevalent. However, IPv4 connectivity will continue to
be provided as a service over these IPv6 only networks. In addition
to providing IPv4 addresses for clients of this service, other IPv4
configuration parameters may also need to be provided, (e.g.
addresses of IPv4-only services).
Several approaches for provisioning such information have been
already been proposed. This document describes one such approach.
2. 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 [RFC2119].
3. Terminology
This document makes use of the following terms:
BOOTREQUESTV6 (TBD): A new type of DHCPv6 Client/Server message
defined in this document. A client sends a
BOOTREQUESTV6 message to a server, which
contains a BOOTP Message Option. Each BOOTP
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Message Option contains a BOOTREQUEST message
that the client uses to request IPv4
configuration parameters from the server.
BOOTREPLYV6 (TBD): A new type of DHCPv6 Client/Server message
defined in this document. A server sends a
BOOTREPLYV6 message containing a BOOTP Message
Option in response to a client's BOOTREQUESTV6
message. Each BOOTP Message Option, wrapped in
a BOOTREPLYV6 message, contains a BOOTREPLY
message. This contains the BOOTREQUEST
response corresponding to a client's
BOOTREQUESTV6 message.
4. Architecture Overview
The architecture described in this document addresses a typical use
case, whereby a DHCP client's uplink supports IPv6 only and the
Service Provider's network supports IPv6 and limited IPv4 services.
In this scenario, the client can only use the IPv6 network to access
IPv4 services and so it must configure IPv4 services using IPv6 as
the underlying transport protocol.
Although the purpose of this document is to address the problem of
communication between DHCPv4 client and DHCPv4 server, the mechanisms
it describes do not restrict the transported types of messages to
DHCPv4. In additional, BOOTP messages can be transported using the
same mechanism.
DHCP clients can be running on CPE devices, end hosts or any other
device which supports the DHCP client function. At the time of
writing, DHCP clients on CPE devices are relatively easier to modify
compared to those implemented on end hosts. As a result, this
document uses the CPE as an example for describing the mechanism.
This doesn't preclude end hosts from implementing the mechanism in
the future.
This mechanism works by carrying encapsulated DHCPv4 messages over
DHCPv6 messages. Figure 1, below, illustrates one possible
deployment architecture.
The DHCP client implements a new DHCPv6 message called BOOTREQUESTV6,
which contains a new option called the BOOTP Message Option. The
format of the option is described in Section 5. The client sends all
DHCPv6 packets, including DHCPv4 over DHCPv6 packets, to the well-
known All_DHCP_Relay_Agents_and_Servers multicast address on the
DHCPv6 server port (UDP port 547).
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The DHCPv6 packet can be transmitted either via Relay Agents or
directly to the server. The server is referred in this document as a
"Unified Server" for its capability of processing regular DHCPv6
traffic as well as DHCPv4 packets wrapped in the BOOTP Message
Option. Server replies with a relevant DHCPv6 packet carrying DHCPv4
response wrapped with the BOOTP Message Option. Clients receive a
response on UDP port 546.
_____________ _____________
/ \ / \
| | | |
+--------+-+ IPv6 +-+-----------+-+ IPv6 +-+--------+
| DHCP | network | DHCP | network | Unified |
| Client +---------+ Relay Agent +---------+ Server |
| (on CPE) | | | | |
+--------+-+ +-+-----------+-+ +-+--------+
| | | |
\_____________/ \_____________/
Figure 1: Architecture Overview
5. BOOTP Message Option Format
The BOOTP Message option carries a BOOTP message that is sent by the
client or the server. Such BOOTP messages exclude any IP or UDP
headers.
The format of the BOOTP Message Option is:
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_BOOTP_MSG | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. BOOTP-message .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: BOOTP Message Option Format
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option-code OPTION_BOOTP_MSG (TBD)
option-len Length of BOOTP message
BOOTP-message The BOOTP message sent by the client or the server.
In a BOOTREQUESTV6 message it contains a BOOTREQUEST
message sent by client. In a BOOTREPLYV6 message it
contains a BOOTREPLY message sent by a server in
response to a client.
6. Client Behavior
When a client requires an IPv4 address and/or other IPv4
configuration parameters, it MUST generate a DHCPv4 message to obtain
them from a DHCP server. This message is stored verbatim in the
BOOTP Message Option carried by the BOOTREQUESTV6 message. A Client
MUST put exactly one BOOTP Message Option into a single BOOTREQUESTV6
message. The Client sends out the BOOTREQUESTV6 message to the Well-
Known multicast address, i.e. All_DHCP_Relay_Agents_and_Servers on
multicast address defined in [RFC3315].
When a client receives a BOOTREPLYV6 message, it MUST look for the
BOOTP Message Option within this message. If this option is not
found, the BOOTREPLYV6 message is discarded. If the BOOTP Message
Option is found, the client extracts the DHCPv4 message it contains
and processes it as described in section 4.4 of [RFC2131].
As the DHCPv4 and DHCPv6 clients are running on the same host, the
client MUST implement [RFC4361] to ensure that the device correctly
identifies itself.
7. Relay Agent Behavior
When a DHCPv6 relay agent receives a BOOTREQUESTV6 message, it MUST
handle the message as described in section 20.1.1 of [RFC3315].
A DHCPv6 relay agent MUST implement the Relay behaviour described in
section 20.1.1 of [RFC3315].
Additionally, the DHCPv6 relay agent MAY allow the configuration of a
dedicated DHCPv4 over DHCPv6 specific destination addresses,
differing from the addresses of the DHCPv6 only server(s). To
implement this function, the relay checks the received DHCPv6 message
type and forwards according to the following logic:
1. If the message type is BOOTREQUESTV6, then the DHCPv6 request is
relayed to the configured DHCPv4 aware unified server's
address(es).
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2. For any other DHCPv6 message type, forward according to section
20 of [RFC3315].
The above logic only allows for separate relay destinations
configured on the relay agent closest to the client (single relay
hop). Multiple relaying hops are not considered in this document.
8. Server Behavior
When a Unified Server receives a BOOTREQUESTV6 message from a client,
it searches for a BOOTP Message Option. If this option is missing,
the server discards the packet. The Server MAY notify an
administrator about the receipt of a malformed packet. The mechanism
for this notification is out of scope for this document
If the server finds a valid BOOTP Message Option, it extracts the
original DHCPv4 message sent by the client. This message is passed
to the DHCPv4 server engine, which generates a response to the as
specified in [RFC2131]. The server places the DHCPv4 response
message, in the payload of a BOOTP Message Option, which it puts into
the BOOTREPLYV6 message.
If the BOOTREQUESTV6 message was received directly by the server, the
BOOTREPLYV6 message MUST be unicast from the interface on which the
original message was received.
If the BOOTREQUESTV6 message was received in a Relay-forward message,
the server creates a Relay-reply message with the BOOTREPLYV6 message
in the payload of a Relay Message Option. This is analogous to other
types of DHCPv6 messages as described in [RFC3315]. The server
unicasts the Relay-reply message directly to the IP address of the
relay agent from which the Relay-forward message was received.
9. Security Considerations
In this specification, DHCPv6 is made a 'transport protocol' for
DHCPv4 messages over an IPv6 network. In order to bypass firewalls
or network authentication gateways, a malicious attacker may leverage
this feature to convey other messages using DHCPv6, i.e. use DHCPv6
as a type of tunnel. However, the potential risk from this is no
greater than with current DHCPv4 and DHCPv6 practice.
10. IANA Considerations
IANA is kindly requested to allocate one DHCPv6 option code to the
OPTION_BOOTP_MSG and two DHCPv6 message type codes to the
BOOTREQUESTV6 and BOOTREPLYV6.
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11. Contributors List
Many thanks to Ted Lemon, Bernie Volz, Tomek Mrugalski, Yuchi Chen
and Cong Liu, for their great contributions to the draft.
12. References
12.1. Normative References
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
2131, March 1997.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC4361] Lemon, T. and B. Sommerfeld, "Node-specific Client
Identifiers for Dynamic Host Configuration Protocol
Version Four (DHCPv4)", RFC 4361, February 2006.
12.2. Informative References
[I-D.ietf-dhc-dhcpv4-over-ipv6]
Cui, Y., Wu, P., Wu, J., and T. Lemon, "DHCPv4 over IPv6
Transport", draft-ietf-dhc-dhcpv4-over-ipv6-06 (work in
progress), March 2013.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
Authors' Addresses
Qi Sun
Tsinghua University
Department of Computer Science, Tsinghua University
Beijing 100084
P.R.China
Phone: +86-10-6278-5822
Email: sunqi@csnet1.cs.tsinghua.edu.cn
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Yong Cui
Tsinghua University
Department of Computer Science, Tsinghua University
Beijing 100084
P.R.China
Phone: +86-10-6260-3059
Email: yong@csnet1.cs.tsinghua.edu.cn
Marcin Siodelski
950 Charter Street
Redwood City, CA 94063
USA
Phone: +1 650 423 1431
Email: msiodelski@gmail.com
Suresh Krishnan
Ericsson
Email: suresh.krishnan@ericsson.com
Ian Farrer
Deutsche Telekom AG
GTN-FM4,Landgrabenweg 151
Bonn, NRW 53227
Germany
Email: ian.farrer@telekom.de
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