draft-ietf-dhc-dhcpv4-over-ipv6-02.txt   draft-ietf-dhc-dhcpv4-over-ipv6-03.txt 
Network Working Group Y. Cui Network Working Group Y. Cui
Internet-Draft P. Wu Internet-Draft P. Wu
Intended status: Standards Track J. Wu Intended status: Standards Track J. Wu
Expires: September 30, 2012 Tsinghua University Expires: November 19, 2012 Tsinghua University
T. Lemon T. Lemon
Nominum, Inc. Nominum, Inc.
March 29, 2012 May 18, 2012
DHCPv4 over IPv6 Transport DHCPv4 over IPv6 Transport
draft-ietf-dhc-dhcpv4-over-ipv6-02 draft-ietf-dhc-dhcpv4-over-ipv6-03
Abstract Abstract
In IPv6 networks, there remains a need to provide IPv4 service for In IPv6 networks, there remains a need to provide IPv4 service for
some residual devices. This document describes a mechanism for some residual devices. This document describes a mechanism for
allocating IPv4 addresses to such devices using DHCPv4 with an IPv6 allocating IPv4 addresses to such devices, using DHCPv4 with an IPv6
transport. It is done by extending DHCP client and server behavior, transport. It is done by putting a special relay agent function
and by adding a new Relay Agent Information option to carry the IPv6 (Client Relay Agent) on the client side, as well as extending the
address of the client. behavior of the server; in the case where DHCP server only supports
IPv4 transport, a relay agent is extended to support IPv6 transport
(IPv6-Transport Relay Agent) and relay DHCP traffic for the server,
with a new Relay Agent Information sub-option added to carry the IPv6
address of the Client Relay Agent.
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
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 30, 2012. This Internet-Draft will expire on November 19, 2012.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Protocol Summary . . . . . . . . . . . . . . . . . . . . . . . 4 4. Protocol Summary . . . . . . . . . . . . . . . . . . . . . . . 4
5. Client Relay Agent IPv6 Address Sub-option . . . . . . . . . . 6 5. Client Relay Agent IPv6 Address Sub-option . . . . . . . . . . 6
6. Client Relay Agent Behavior . . . . . . . . . . . . . . . . . . 6 6. Client Relay Agent Behavior . . . . . . . . . . . . . . . . . 7
7. IPv6-Transport Server Behavior . . . . . . . . . . . . . . . . 7 7. IPv6-Transport Server Behavior . . . . . . . . . . . . . . . . 8
8. IPv6-Transport Relay Agent Behavior . . . . . . . . . . . . . . 8 8. IPv6-Transport Relay Agent Behavior . . . . . . . . . . . . . 8
9. Security Consideration . . . . . . . . . . . . . . . . . . . . 8 9. Security Consideration . . . . . . . . . . . . . . . . . . . . 9
10. IANA consideration . . . . . . . . . . . . . . . . . . . . . . 8 10. IANA consideration . . . . . . . . . . . . . . . . . . . . . . 9
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 9 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 9
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 12. Appendix: Discussion on One Host Retrieving Multiple
12.1. Normative References . . . . . . . . . . . . . . . . . . . 9 Addresses through One CRA . . . . . . . . . . . . . . . . . . 10
12.2. Informative References . . . . . . . . . . . . . . . . . . 9 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
13.1. Normative References . . . . . . . . . . . . . . . . . . 11
13.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction 1. Introduction
DHCPv4 [RFC2131] was not designed with IPv6 in mind: DHCPv4 cannot DHCPv4 [RFC2131] was not designed with IPv6 in mind: DHCPv4 cannot
operate on an IPv6 network. However, as dual-stack networks become a operate on an IPv6 network. However, as dual-stack networks become a
reality, the need arises to allocate IPv4 addresses in an IPv6 reality, the need arises to allocate IPv4 addresses in an IPv6
environment. To meet this demand, this document extends DHCPv4 to environment. To meet this demand, this document extends the DHCPv4
allow the use of an IPv6 network for transport. protocol to allow the use of an IPv6 network for transport.
A typical scenario that probably requires this feature is IPv4-over- A typical scenario that probably requires this feature is IPv4-over-
IPv6 hub and spoke tunnel [RFC4925]. In this scenario, IPv4-over- IPv6 hub and spoke tunnel [RFC4925]. In this scenario, IPv4-over-
IPv6 tunnel is used to provide IPv4 connectivity to end users (hosts IPv6 tunnel is used to provide IPv4 connectivity to end users (hosts
or end networks) across an IPv6 network. If the IPv4 addresses of or end networks) across an IPv6 network. If the IPv4 addresses of
the end users are provisioned by the concentrator side, then the the end users are provisioned by the concentrator side, then the
provisioning process should be able to cross the IPv6 network, too. provisioning process should be able to cross the IPv6 network. One
One such tunnel mechanism is demonstrated in such tunnel mechanism is demonstrated in
[I-D.ietf-softwire-public-4over6]. DHCPv4 over IPv6 would be a [I-D.ietf-softwire-public-4over6]. DHCPv4 over IPv6 would be a
generic solution for this scenario. generic solution for this scenario.
Three main flavours of solutions may be considered: Three main flavors of solutions may be considered:
o Use DHCPv6 instead of DHCPv4, to provision IPv4-related o Use DHCPv6 instead of DHCPv4, to provision IPv4-related
connectivity. In DHCPv6, the provisioned IPv4 address can be connectivity. In DHCPv6, the provisioned IPv4 address can be
embedded into IPv6 address, or carried within a new option. Along embedded into IPv6 address, or carried within a new option. Along
with that, dedicated options are needed to convey IPv4-related with that, dedicated options are needed to convey IPv4-related
information, such as the IPv4 address of DNS server, NTP server, information, such as the IPv4 address of DNS server, NTP server,
etc. Therefore it will put a certain amount of IPv6-unrelated etc. Therefore it will put a certain amount of IPv6-unrelated
information into DHCPv6 protocol. information into DHCPv6 protocol.
o Use DHCPv4 and tunnel DHCPv4-in-IPv4 messages over IPv6. Unlike o Use DHCPv4 and tunnel DHCPv4-in-IPv4 messages over IPv6. Unlike
the previous approach where DHCPv6 is used for both IPv4 and IPv6 the previous approach where DHCPv6 is used for both IPv4 and IPv6
connectivity, this approach consists in preserving the separation connectivity, this approach consists in preserving the separation
between IPv4 and IPv6 connectivity information. It allows to between IPv4 and IPv6 connectivity information. It allows to
maintain the IPv4 service without major modification of IPv6- maintain the IPv4 service without major modification of IPv6-
related provisioning resources, and sustains DHCPv4 to be the related provisioning resources, and sustains DHCPv4 to be the
IPv4-related information carrier. However, this approach enforces IPv4-related information carrier. However, this approach enforces
an IPv4-in-IPv6 tunnel on DHCP, and requires extra efforts to an IPv4-in-IPv6 tunnel on DHCP, and subsequently requires extra
maintain tunnel endpoint information for encapsulation use. efforts to maintain tunnel endpoint information for encapsulation
use.
o Use DHCPv4 and extend it to work over IPv6 transport. Instead of o Use DHCPv4 and extend it to work on IPv6 transport. Instead of
relying on IPv4-in-IPv6 tunnel, this flavour uses IPv6 directly relying on IPv4-in-IPv6 tunnel, this flavor uses IPv6 directly for
for DHCP message transport, and it keeps the advantage of DHCP message transport, and it keeps the advantage of separation
separation with IPv6 connectivity information. This document with IPv6 connectivity information. This document focuses on this
focuses on this flavour. The document will define the extensions flavor. The document defines the behavior of extended DHCPv4
of DHCPv4 protocol behavior, as well as a new suboption of the components, as well as a new sub-option of the Relay Agent
Relay Agent Information Option, to fully support DHCPv4 over IPv6. Information Option, to support DHCPv4 over IPv6.
2. Requirements Language 2. 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 [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Terminology 3. Terminology
This document makes use of the following terms: This document makes use of the following terms:
o DHCPv4: IPv4 Dynamic Host Configuration Protocol [RFC2131]. o DHCPv4: IPv4 Dynamic Host Configuration Protocol [RFC2131].
skipping to change at page 4, line 14 skipping to change at page 4, line 17
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 [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Terminology 3. Terminology
This document makes use of the following terms: This document makes use of the following terms:
o DHCPv4: IPv4 Dynamic Host Configuration Protocol [RFC2131]. o DHCPv4: IPv4 Dynamic Host Configuration Protocol [RFC2131].
o Client Relay Agent(CRA): a special DHCPv4 Relay Agent that sits on o Client Relay Agent(CRA): a special DHCPv4 Relay Agent which works
the same, IPv6-accessable host with the DHCPv4 client. CRA works as a "proxy" between DHCPv4 client and the IPv6 network by
as a "bridge" between DHCPv4 client and the IPv6 network, to converting between IPv4 transport and IPv6 transport. A CRA
convert between IPv4 transport and IPv6 transport. either sits on the same, IPv6-accessable host with the DHCPv4
client, or sits on the same link with the host.
o On-link Client Relay Agent(LCRA): a CRA sits on the link of the o Host Client Relay Agent(HCRA): a CRA which sits on the same, IPv6-
host rather then inside the host. accessible host with the DHCPv4 client.
o On-Link Client Relay Agent(LCRA): a CRA which sits on the same
link with the host that runs DHCPv4 client.
o IPv6-Transport Server(TSV): a DHCPv4 Server that supports IPv6 o IPv6-Transport Server(TSV): a DHCPv4 Server that supports IPv6
transport. TSV can listen on IPv6 for incoming DHCPv4 messages, transport. TSV listens on IPv6 for incoming DHCPv4 messages, and
and send DHCPv4 messages in IPv6 packets. sends DHCPv4 messages in IPv6 packets.
o IPv6-Transport Relay Agent(TRA): a DHCPv4 Relay Agent that o IPv6-Transport Relay Agent(TRA): a DHCPv4 Relay Agent that
supports IPv6 transport. TRA sits on a machine which has both supports IPv6 transport. TRA sits on a machine which has both
IPv6 and IPv4 connectivity, and relays DHCP messages between CRA IPv6 and IPv4 connectivity, and relays DHCP messages between CRA
and normal DHCPv4 server. and regular DHCPv4 server. Unlike CRA, TRA sits on the remote end
of IPv6 network, and communicates with DHCPv4 server through IPv4.
o Client Relay Agent IPv6 Address Sub-option(CRA6ADDR suboption): a o Client Relay Agent IPv6 Address Sub-option(CRA6ADDR sub-option): a
new suboption of DHCP Relay Agent Information Option [RFC3046] new sub-option of DHCP Relay Agent Information Option [RFC3046]
defined in this document. CRA6ADDR suboption is used by TRA to defined in this document. CRA6ADDR sub-option is used by TRA to
carry the IPv6 address of a CRA. carry the IPv6 address of a CRA.
4. Protocol Summary 4. Protocol Summary
The scenario for DHCPv4 over IPv6 transport is shown in Figure 1. The scenario for DHCPv4 over IPv6 transport is shown in Figure 1.
DHCPv4 clients and DHCPv4 server/relay are separated by an IPv6 DHCPv4 clients and DHCPv4 server/relay are separated by an IPv6
network in the middle. DHCP messages between a client and the network in the middle. DHCP messages between a client and the
server/relay cannot naturally be forwarded to each other because they server/relay cannot naturally be forwarded to each other because they
are by default IPv4 UDP packets, either unicast or broadcast. To are by default IPv4 UDP packets, either unicast or broadcast. To
bridge this gap, both the client side and the server/relay side bridge this gap, both the client side and the server/relay side
should enable DHCPv4 over IPv6 transport. More precisely, they should enable DHCPv4 over IPv6 transport. More precisely, they
should support delivering and receiving DHCP messages in IPv6 UDP should support delivering and receiving DHCP messages in IPv6 UDP
packets and thereby traverse the IPv6 network. packets and thereby traverse the IPv6 network.
On the client side, a special relay agent called Client Relay Agent On the client side, a special relay agent called Client Relay Agent
is placed on the same host with the client, or on the link of the is placed on the same host with the client, or on the link of the
client. CRA is used to relay DHCP messages from the client to the host. CRA is used to relay DHCP messages from the client to the
server, and from the server to the client. CRA sends DHCPv4 messages server, and from the server to the client. CRA sends DHCPv4 messages
to the server through unicast IPv6 UDP, and receives unicast IPv6 UDP to the server through unicast IPv6 UDP, and receives unicast IPv6 UDP
packets with the DHCPv4 messages from the server. By using CRA, no packets with the DHCPv4 messages from the server. By using CRA, no
extension is required on the DHCP client. extension is required on the DHCP client.
+-------------------------+ +-------------------------+
+------+ | +------+ |
|DHCPv4| | |DHCPv4| |
|Client| +-------+ |Client| +-------+
+------+ |DHCPv4 | +------+ |DHCPv4 |
skipping to change at page 5, line 24 skipping to change at page 5, line 33
+------+ |Relay | +------+ |Relay |
|DHCPv4| +-------+ |DHCPv4| +-------+
|Client| | |Client| |
+------+ | +------+ |
+-------------------------+ +-------------------------+
Figure 1 Scenario of DHCPv4 over IPv6 Transport Figure 1 Scenario of DHCPv4 over IPv6 Transport
The IPv6-Transport DHCPv4 server can receive DHCP messages delivered The IPv6-Transport DHCPv4 server can receive DHCP messages delivered
in IPv6 UDP from CRA, and send out DHCP messages to CRA using IPv6 in IPv6 UDP from CRA, and send out DHCP messages to CRA using IPv6
UDP(figure 2(a)). TSV should send DHCP messages to the IPv6 address UDP (figure 2(a)). TSV should send DHCP messages to the IPv6 address
from which it receives relevant DHCP messages earlier. from which it receives relevant DHCP messages earlier.
When CRAs communicate with an IPv6-Transport Relay Agent rather than When CRAs communicate with an IPv6-Transport Relay Agent rather than
with a server directly, the situation will become a little more with a server directly, the situation will become a little more
complicated. Besides the IPv6 communication with CRA, TRA also complicated. Besides the IPv6 communication with CRA, TRA also
communicates with a regular DHCPv4 server through IPv4. Therefore, communicates with a regular DHCPv4 server through IPv4. Therefore,
when TRA relays DHCP messages between a CRA and the DHCPv4 server, it when TRA relays DHCP messages between a CRA and the DHCPv4 server, it
receives DHCP message from the CRA in IPv6 and sends it to the server receives DHCP message from the CRA in IPv6 and sends it to the server
in IPv4, while receives DHCP message from the server in IPv4 and in IPv4, as well as receives DHCP message from the server in IPv4 and
sends it to the CRA in IPv6. TRA has to use the DHCP Relay Agent sends it to the CRA in IPv6. TRA has to use the DHCP Relay Agent
Information Option(Option 82) to record the IPv6 address of a CRA, Information Option (Option code 82) to record the IPv6 address of the
which will be used as forwarding destination when relaying a DHCP CRA, which will be used as forwarding destination when relaying a
message from the server. Since Option 82 doesn't have an existing DHCP message from the server. Since Option 82 doesn't have an
suboption that fits in the case, this document defines a new Client existing sub-option that fits in the case, this document defines a
Relay Agent IPv6 Address Sub-option. new Client Relay Agent IPv6 Address Sub-option. The DHCPv4 server
MUST support the new sub-option in this case.
+------+ +------+ +------+ +------+
|client| IPv6 network |TSV | |client| IPv6 network |TSV |
|+CRA |----------------| | |+HCRA |----------------| |
+------+ +------+ +------+ +------+
+------+ +------+ +------+
|client| |LCRA | IPv6 network |TSV |
| |--| |----------------| |
+------+ +------+ +------+
(a)client--server case (a)client--server case
+------+ +------+ +------+ +------+ +------+ +------+
|client| IPv6 network |TRA | IPv4 network |server| |client| IPv6 network |TRA | IPv4 network |server|
|+CRA |----------------| |--------------| | |+HCRA |----------------| |--------------| |
+------+ +------+ +------+ +------+ +------+ +------+
+------+ +------+ +------+ +------+
|client| |LCRA | IPv6 network |TRA | IPv4 network |server|
| |--| |----------------| |--------------| |
+------+ +------+ +------+ +------+
(b)client--relay--server case (b)client--relay--server case
Figure 2 Protocol Summary Figure 2 Protocol Summary
5. Client Relay Agent IPv6 Address Sub-option 5. Client Relay Agent IPv6 Address Sub-option
This suboption MUST be added by a DHCPv4 TRA. It encodes the IPv6 This sub-option MUST be added by a DHCPv4 TRA. It encodes the IPv6
address of the host from which a DHCPv4-in-IPv6 CRA-to-TRA message address of the machine from which a DHCPv4-in-IPv6 CRA-to-TRA message
was received. It is intended for the TRA to relay DHCPv4 replies was received. It is intended for the TRA to relay DHCPv4 replies
back to the proper CRA. To be more specific, the TRA uses the IPv6 back to the proper CRA. To be more specific, the TRA uses the IPv6
address encoded in this suboption as the destination IPv6 address address encoded in this sub-option as the destination IPv6 address
when relaying a DHCPv4 reply to IPv6 network. when relaying a DHCPv4 reply to IPv6 network.
The CRA IPv6 address MUST be unique in the IPv6 domain. The CRA IPv6 address MUST be unique in the IPv6 domain.
The CRA6ADDR suboption has a fixed length of 18 octets. The SubOpt The CRA6ADDR sub-option has a fixed length of 18 octets. The SubOpt
code is tbd by IANA, the length field should be 16, and the following code is tbd by IANA, the length field is 16, and the following 16
16 octets contain the CRA IPv6 address. octets contain the CRA IPv6 address.
DHCP servers handles it following the standard option 82 procedure DHCP servers handle it following the standard option 82 procedure
defined in [RFC3046]. DHCP servers MAY use this suboption to select defined in [RFC3046]. DHCP servers MAY use this sub-option to select
parameters specific to particular hosts. Servers MAY parse this parameters specific to particular hosts. Servers MAY parse this sub-
suboption and extract the semantic of IPv6 address. option and extract the IPv6 address.
SubOpt Len Agent Remote ID SubOpt Len Agent Remote ID
+------+------+------+------+------+- -+------+ +------+------+------+------+------+- -+------+
| tbd | 16 | a1 | a2 | a3 | ... | a16 | | tbd | 16 | a1 | a2 | a3 | ... | a16 |
+------+------+------+------+------+- -+------+ +------+------+------+------+------+- -+------+
Figure 3 Client Relay Agent IPv6 Address Sub-option format Figure 3 Client Relay Agent IPv6 Address Sub-option format
6. Client Relay Agent Behavior 6. Client Relay Agent Behavior
A Client Relay Agent sits on the same host with the DHCPv4 client. A Client Relay Agent sits on the same host with the DHCPv4 client
CRA is a special type of relay agent, which relays DHCPv4 messages (HCRA), or on the link of the host (LCRA). CRA is a special type of
between regular client and TSV/TRA. The communication between CRA relay agent, which relays DHCPv4 messages between regular client and
and the client happens within the machine using IPv4, and the TSV/TRA. The communication between CRA and the client happens inside
communication between CRA and TSV/TRA happens on the IPv6 network the last-hop local network using IPv4, and the communication between
using IPv6. CRA and TSV/TRA happens on the IPv6 network using IPv6.
A CRA is configured with one or more IPv6 addresses of TSV/TRA. This A CRA is configured with one or more IPv6 addresses of TSV/TRA. This
configuration is provided before DHCPv4 process, for example through configuration is provided before DHCPv4 process, for example through
DHCPv6 option, or by some other mechanisms depending on the DHCPv6 option, or by some other mechanisms depending on the
application scenarios. application scenarios.
A CRA listens for DHCP messages on IPv4 UDP port 67. When it A CRA listens for DHCP messages on IPv4 UDP port 67. When it
receives from IPv4 any DHCP message with bootp op field = 1, it receives from IPv4 any DHCP message with bootp op field = 1, it
forwards the message using the standard DHCP relay agent format, but forwards the message using the standard DHCP relay agent format, but
over UDPv6, with source port 67 and destination port 67. Here the over UDPv6, with source port 67 and destination port 67. The CRA
CRA MUST NOT include an option 82 or modify the giaddr field of the forwards the message to each of the TSV or TRA with which it is
DHCP message. The CRA forwards the message to each of the DHCP configured. The CRA SHOULD use a global IPv6 address if it has one.
server or relay agent with which it is configured. The CRA MUST use
a global IPv6 address if it has onbe.
A CRA also listens for DHCP messages on IPv6 UDP port 68. When it A CRA also listens for DHCP messages on IPv6 UDP port 68. When it
receives from IPv6 any DHCP message with bootp op field = 2, the CRA receives from IPv6 any DHCP message with bootp op field = 2, the CRA
checks to see if the message contains option 82, and if so, it checks to see if the message contains option 82, and if so, it
discards the message. Otherwise, it delivers the message to the DHCP discards the message. Otherwise, it delivers the message to the DHCP
client using IPv4. client using IPv4.
A CRA can also sits on the link of the host (LCRA). The basic The basic functionality of HCRA and LCRA are the same. The
functionility of LCRA is the same with CRA. LCRA SHOULD NOT include difference is that, when relaying DHCP messages, the HCRA MUST NOT
a option 82 or modify the giaddr of DHCP message. If it has to, include an option 82 or modify the giaddr field of the DHCP message,
while in the LCRA case, it SHOULD NOT include an option 82 or modify
the giaddr of DHCP message. If it has to,
[I-D.ietf-dhc-dhcpv4-relay-encapsulation] can be used as the solution [I-D.ietf-dhc-dhcpv4-relay-encapsulation] can be used as the solution
to the coexistence of LCRA and TRA. LCRA does not necessarily need to the coexistence of LCRA and TRA.
an IPv4 address, though it may be configured with one.
A CRA MUST only serve the client inside the same host, while the LCRA A HCRA MUST only serve the client inside the same host, while the
MUST serve any client on the link. When the IPv6 address of TSV/TRA LCRA SHOULD serve any client on the link. When the IPv6 address of
is provisioned, the DHCP client uses CRA; else the client uses LCRA. TSV/TRA is provisioned to the DHCP client, it uses HCRA; else the
client depends on LCRA. A HCRA serves only one link; the multiple
link case MUST be handled by multiple HCRA instances. A LCRA does
not necessarily need an IPv4 address, though it may be configured
with one.
7. IPv6-Transport Server Behavior 7. IPv6-Transport Server Behavior
To support IPv6 transport, the behavior of DHCPv4 server should be To support IPv6 transport, the behavior of DHCPv4 server is extended.
extended. The IPv6-Transport Server can listen on IPv6 port 67 for The IPv6-Transport Server can listen on IPv6 port 67 for DHCPv4
DHCPv4 messages, and send DHCPv4 messages through IPv6. messages, and send DHCPv4 messages through IPv6.
A TSV listens for DHCP messages on IPv6 UDP port 67. When it A TSV listens for DHCP messages on IPv6 UDP port 67. When it
receives from IPv6 a DHCP message, it MUST record the IPv6 source receives from IPv6 a DHCP message, it MUST record the IPv6 source
address of that message and retain it as the return address of the address of that message and retain it as the return address of the
message. That is to say, when sometime later the TSV responds to message. That is to say, when sometime later the TSV responds to
this message, it MUST send the reply message to the IPv6 return this message, it MUST send the reply message to the IPv6 return
address retained earlier, with destination port 68. When filling in address retained earlier, with destination port 68. When filling in
the server id option of DHCP replies, the TSV MUST choose an IPv4 the server id option of DHCP replies, the TSV MUST choose an IPv4
address which is reachable from the client once the residual IPv4 address which is reachable from the client once the residual IPv4
serivice is set up. This follows the server id option requirement in service is set up. This follows the server id option requirement in
[RFC2131]. The rest of TSV DHCP process is the same with normal [RFC2131]. The rest of TSV DHCP process is the same with normal
DHCPv4 server. A TSV can also listen on IPv4 UDP port 67 like a DHCPv4 server. A TSV MAY also listen on IPv4 UDP port 67 like a
normal DHCPv4 server, and process normally when receives IPv4 DHCPv4 normal DHCPv4 server, and process normally when receives IPv4 DHCPv4
message. message.
This document places no new requirements on DHCPv4 servers that do This document places no new requirements on DHCPv4 servers that do
not listen on UDPv6--in order to use an IPv4-only DHCPv4 server not listen on UDPv6 (other than to support the CRA6ADDR
through an IPv6 connection, a TRA is required. sub-option)--in order to use an IPv4-only DHCPv4 server through an
IPv6 connection, a TRA is required.
8. IPv6-Transport Relay Agent Behavior 8. IPv6-Transport Relay Agent Behavior
An IPv6-Transport Relay Agent sits between IPv6 network and IPv4 An IPv6-Transport Relay Agent sits between IPv6 network and IPv4
network, and relays DHCPv4 message between CRAs and IPv4-only DHCPv4 network, and relays DHCPv4 message between CRAs and IPv4-only DHCPv4
server. The communication between CRAs and the TRA uses IPv6, while server. The communication between CRAs and the TRA uses IPv6, while
the communication between TRA and server uses IPv4. A TRA listens on the communication between the TRA and the server uses IPv4. A TRA
IPv6 UDP port 67 for DHCP messages with bootp op field = 1, as well listens on IPv6 UDP port 67 for DHCP messages with bootp op field =
as IPv4 UDP port 68 for DHCP messages with bootp op field = 2. 1, as well as IPv4 UDP port 68 for DHCP messages with bootp op field
= 2.
When relaying a DHCP message from CRA to server, TRA MUST add an When relaying a DHCP message from CRA to server, TRA MUST add an
option 82 with a CRA6ADDR suboption. This suboption contains the option 82 with a CRA6ADDR sub-option. This sub-option contains the
IPv6 source address of the message (the CRA's IPv6 address) which is IPv6 source address of the message (the CRA's IPv6 address) which is
retained when the message is received in IPv6. The TRA MUST also retained when the message is received in IPv6. The TRA MUST also
store the IPv4 address of itself in the giaddr field of the DHCP store the IPv4 address of itself in the giaddr field of the DHCP
message. The TRA MAY include a Link Selection Suboption [RFC3527] to message. The TRA MAY include a Link Selection sub-option [RFC3527]
indicate to the DHCP server which link to use when choosing an IP to indicate to the DHCP server which link to use when choosing an IP
address. address.
When receiving a DHCP message from the DHCP server, if the option 82 When receiving a DHCP message from the DHCP server, if the option 82
in the message contains no CRA6ADDR suboption, the TRA MUST discard in the message contains no CRA6ADDR sub-option, the TRA MUST discard
the message. Otherwise, it processes it as required by [RFC3046], the message. Otherwise, it processes it as required by [RFC3046],
and forwards it to the IPv6 address recorded in the CRA6ADDR and forwards it to the IPv6 address recorded in the CRA6ADDR sub-
suboption, with source port 67 and destination port number 68. TRA option, with source port 67 and destination port number 68. TRA
SHOULD drop DHCPv4-over-IPv6 traffic that is not originated from SHOULD drop DHCPv4-over-IPv6 traffic that is not originated from
configured server address. configured server address.
9. Security Consideration 9. Security Consideration
This mechanism may rise a new form of DHCP protocol attack. A This mechanism may rise a new form of DHCP protocol attack. A
malicious attacker in IPv6 can interference with the DHCPv4 process malicious attacker in IPv6 can interference with the DHCPv4 process
by inject fake DHCPv4-in-IPv6 messages which will be handled by TSV by inject fake DHCPv4-in-IPv6 messages which will be handled by TSV
or TRA. However, the damage is the same with the known DHCPv4 attack or TRA. However, the damage is the same with the known DHCPv4 attack
happened in IPv4. The only difference is the attacker and the victim happened in IPv4. The only difference is the attacker and the victim
could locate in different address families. could locate in different address families.
Another impact is DHCP filtering. There are firewalls today capable Another impact is DHCP filtering. There are firewalls today capable
of filtering DHCP traffic (DHCPv4 over IPv4 and DHCPv6 over IPv6 of filtering DHCP traffic (DHCPv4 over IPv4 and DHCPv6 over IPv6
packages). The DHCP messages with the new, DHCPv4-in-IPv6 style may packages). The DHCP messages with the new, DHCPv4-in-IPv6 style may
bypass these firewalls. Nevertheless it is not difficult for them to bypass these firewalls. Nevertheless it is not difficult for them to
make some slight modification and adapt to the new DHCPv4 message make some slight modification and adapt to the new DHCPv4 message
pattern. pattern.
10. IANA consideration 10. IANA consideration
IANA is requested to assign one new suboption code from the registry
IANA is requested to assign one new sub-option code from the registry
of DHCP Agent Sub-Option Codes maintained in of DHCP Agent Sub-Option Codes maintained in
http://www.iana.org/assignments/bootp-dhcp-parameters. This http://www.iana.org/assignments/bootp-dhcp-parameters. This sub-
suboption code will be assigned to the Client Relay Agent IPv6 option code will be assigned to the Client Relay Agent IPv6 Address
Address Sub-option. Sub-option.
11. Contributors 11. Contributors
Francis Dupont and Tomek Mrugalski. The following gentlemen also contributed to the effort:
12. References Francis Dupont
Internet Systems Consortium, Inc.
12.1. Normative References Email: fdupont@isc.org
Tomasz Mrugalski
Internet Systems Consortium, Inc.
[RFC2119] Bradner, S., "Key words Email: tomasz.mrugalski@gmail.com
for use in RFCs to
Indicate Requirement
Levels", BCP 14, RFC 2119,
March 1997.
[RFC2131] Droms, R., "Dynamic Host Dmitry Anipko
Configuration Protocol", Microsoft Corporation
RFC 2131, March 1997.
[RFC3046] Patrick, M., "DHCP Relay Email: danipko@microsoft.com
Agent Information Option",
RFC 3046, January 2001.
[RFC3527] Kinnear, K., Stapp, M., 12. Appendix: Discussion on One Host Retrieving Multiple Addresses
Johnson, R., and J. through One CRA
Kumarasamy, "Link
Selection sub-option for
the Relay Agent
Information Option for
DHCPv4", RFC 3527,
April 2003.
[RFC4925] Li, X., Dawkins, S., Ward, This document is written with the intention of supporting a use case
D., and A. Durand, where a single DHCP client is configuring a single tunnel endpoint
"Softwire Problem per physical link. The technique described in this document could be
Statement", RFC 4925, used by a host needing to configure more than one tunnel endpoint on
July 2007. the same physical link, i.e., to retrieve multiple addresses through
the same CRA. However, the following additional behavior is REQUIRED
to support this case.
12.2. Informative References DHCP server implementing this specification MUST implement Client
Identifier Option in DHCP server replies [I-D.ietf-dhc-client-id].
[I-D.ietf-dhc-dhcpv4-relay-encapsulation] Lemon, T., Deng, H., and In general this specification is intended not to require modification
L. Huang, "Relay Agent of DHCP clients. However, DHCP clients being used to configure
Encapsulation for DHCPv4", multiple tunnel endpoints have to be modified; otherwise there is no
relay-encapsulation-01 way for such DHCP clients to differentiate between DHCP responses.
(work in progress), Therefore, in such case, the DHCP client using this specification
July 2011. MUST use a different client identifier for each tunnel endpoint being
configured. Such DHCP clients MUST examine the response from the
DHCP server and use the client identifier to differentiate between
the DHCP client state machines for each tunnel endpoint.
[I-D.ietf-softwire-public-4over6] Cui, Y., Wu, J., Wu, P., In order to satisfy the requirement that client identifiers be
Metz, C., Vautrin, O., and unique, DHCP clients configuring multiple tunnel endpoints MUST
Y. Lee, "Public IPv4 over implement Node-specific Client Identifiers for DHCPv4 [RFC4361].
IPv6 Access Network", draf Such clients MUST use a different IAID for each tunnel endpoint.
t-ietf-softwire-public-
4over6-01 (work in It is assumed here that every client state machine on a multiple-
progress), March 2012. tunnel-endpoint link can hear all the DHCP messages (and subsequently
accept the messages intended for it). How this is accomplished is
left to the implementor. However, implementations MUST follow this
requirement; otherwise, it will be impossible for multiple tunnel
endpoints to be successfully configured. The easiest way to
accomplish this is to have a single DHCP client process with multiple
DHCP state machines, and to dispatch each DHCP message to the correct
DHCP client state machine using the client identifier. However, this
is not REQUIRED; any mechanism that results in client state machines
receiving the messages that are intended for them will suffice.
13. References
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997.
[RFC3046] Patrick, M., "DHCP Relay Agent Information Option",
RFC 3046, January 2001.
[RFC3527] Kinnear, K., Stapp, M., Johnson, R., and J. Kumarasamy,
"Link Selection sub-option for the Relay Agent Information
Option for DHCPv4", RFC 3527, April 2003.
[RFC4361] Lemon, T. and B. Sommerfeld, "Node-specific Client
Identifiers for Dynamic Host Configuration Protocol
Version Four (DHCPv4)", RFC 4361, February 2006.
[RFC4925] Li, X., Dawkins, S., Ward, D., and A. Durand, "Softwire
Problem Statement", RFC 4925, July 2007.
13.2. Informative References
[I-D.ietf-dhc-client-id]
Swamy, N., Halwasia, G., and S. Unit, "Client Identifier
Option in DHCP Server Replies",
draft-ietf-dhc-client-id-02 (work in progress),
March 2012.
[I-D.ietf-dhc-dhcpv4-relay-encapsulation]
Lemon, T., Deng, H., and L. Huang, "Relay Agent
Encapsulation for DHCPv4",
draft-ietf-dhc-dhcpv4-relay-encapsulation-01 (work in
progress), July 2011.
[I-D.ietf-softwire-public-4over6]
Cui, Y., Wu, J., Wu, P., Metz, C., Vautrin, O., and Y.
Lee, "Public IPv4 over IPv6 Access Network",
draft-ietf-softwire-public-4over6-01 (work in progress),
March 2012.
Authors' Addresses Authors' Addresses
Yong Cui Yong Cui
Tsinghua University Tsinghua University
Department of Computer Science, Tsinghua University Department of Computer Science, Tsinghua University
Beijing 100084 Beijing 100084
P.R.China P.R.China
Phone: +86-10-6260-3059 Phone: +86-10-6260-3059
EMail: cuiyong@tsinghua.edu.cn Email: yong@csnet1.cs.tsinghua.edu.cn
Peng Wu Peng Wu
Tsinghua University Tsinghua University
Department of Computer Science, Tsinghua University Department of Computer Science, Tsinghua University
Beijing 100084 Beijing 100084
P.R.China P.R.China
Phone: +86-10-6278-5822 Phone: +86-10-6278-5822
EMail: pengwu.thu@gmail.com Email: pengwu.thu@gmail.com
Jianping Wu Jianping Wu
Tsinghua University Tsinghua University
Department of Computer Science, Tsinghua University Department of Computer Science, Tsinghua University
Beijing 100084 Beijing 100084
P.R.China P.R.China
Phone: +86-10-6278-5983 Phone: +86-10-6278-5983
EMail: jianping@cernet.edu.cn Email: jianping@cernet.edu.cn
Ted Lemon Ted Lemon
Nominum, Inc. Nominum, Inc.
2000 Seaport Blvd 2000 Seaport Blvd
Redwood City 94063 Redwood City 94063
USA USA
Phone: +1-650-381-6000 Phone: +1-650-381-6000
EMail: mellon@nominum.com Email: mellon@nominum.com
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