Softwire WG I. Farrer
Internet-Draft Deutsche Telekom AG
Intended status: Standards Track Q. Sun
Expires: January 5, 2016 Y. Cui
Tsinghua University
July 4, 2015
DHCPv4 over DHCPv6 Source Address Option
draft-fsc-softwire-dhcp4o6-saddr-opt-02
Abstract
DHCPv4 over DHCPv6 [RFC7341] describes a mechanism for dynamically
configuring IPv4 over an IPv6-only network. For DHCPv4 over DHCPv6
to function with some IPv4-over-IPv6 softwire mechanisms and
deployment scenarios, the operator must learn the /128 IPv6 address
that the client will use as the source of IPv4-in-IPv6 tunnel. This
address, in conjunction with the IPv4 address and the Port Set ID
allocated to the DHCP 4o6 client are used to create a binding table
entry in the softwire tunnel concentrator. This memo defines two
DHCPv6 options used to communicate the source tunnel IPv6 address
between the DHCP 4o6 client and server. It is designed to work in
conjunction with the IPv4 address allocation process.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on January 5, 2016.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
4. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 3
5. IPv6/IPv4 Binding Message Flow . . . . . . . . . . . . . . . 4
6. DHCPv6 Options . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. DHCPv4 over DHCPv6 Source Address Hint Option . . . . . . 6
6.2. DHCPv4 over DHCPv6 Source Address Option . . . . . . . . 6
6.3. Border Router Prefix Option . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . 8
10.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
Deterministic IPv4-over-IPv6 transition technologies require that
elements are pre-configured with binding rules for routing traffic to
clients. This places a constraint on the location of the client's
tunnel endpoint: The tunnel endpoint has to be a pre-determined
prefix which is usually be configured on the home gateway device.
[I-D.ietf-softwire-map-dhcp] describes a DHCPv6 based mechanism for
provisioning such deterministic softwires.
If a dynamic provisioning model is used, such as using DHCPv4 over
DHCPv6, then pre-configuation of the softwire elements is not
possible and client rules must be created/deleted in line with the
allocation of IPv4 addresses to clients. This has the benefit of
removing the fixed address constraint for the client's tunnel
endpoint, as the address that the client will use can be learnt when
the tunnel is provisioned. The operator's tunnel concentrator(s) can
then be configured with the binding rule.
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This document describes a mechanism for informing the service
provider of the binding between the dynamically allocated IPv4
address and Port Set ID (learnt through DHCPv4 over DHCPv6) and the
IPv6 address that the softwire Initiator will use for accessing IPv4-
over-IPv6 services. It is used with DHCPv4 over DHCPv6 [RFC7341]
message flows to communicate the binding over the IPv6-only network.
The service provider can then use this binding information to
provision other functional elements in their network accordingly,
e.g. using the client's binding information to synchronise the
binding table in the border router.
The mechanism allows much more flexibility in the location of the
IPv4-over-IPv6 tunnel endpoint, as the IPv6 address is dynamically
signalled back to the service provider. The DHCP 4o6 client and
tunnel client could be run on end devices attached to any routable
IPv6 prefix allocated to an end-user, located anywhere within an
arbitrary home network topology.
2. Applicability
The mechanism described in this document is only suitable for use for
provisioning softwire clients via DHCP 4o6. The options described
here are only applicable within the DHCP 4o6 message exchange
process. Current mechanisms suitable for extending to incorporate
DHCPv4 over DHCPv6 with dynamic IPv4 address leasing include
[I-D.ietf-softwire-map] and [I-D.ietf-softwire-lw4over6].
3. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
4. Solution Overview
The solution in this document is intended for the dynamic
establishment of IPv4-over-IPv6 softwires. DHCP 4o6 [RFC7341]
supports dynamically allocating (shared) IPv4 address. For a
softwire to be successfully created, the IPv4 address has to be
linked to the client's IPv6 tunnel source address. Within this
process, the DHCP 4o6 client uses a DHCPv6 option to signal its
tunnel source IPv6 address to the DHCP 4o6 server so that the
operator's provisioning system can create the binding and configure
the tunnel concentrator accordingly.
Two new DHCPv6 options are defined in this memo:
OPTION_DHCP4O6_SADDR_HINT and OPTION_DHCP4O6_SADDR. They are
intended to be used alongside the normal DHCPv4 IPv4 address
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allocation message flow in the context of DHCPv4 over DHCPv6
[RFC7341]. If a DHCP 4o6 client supports this mechanism, it MUST
include the code of OPTION_DHCP4O6_SADDR_HINT in the Option Request
Option (ORO) [RFC3315] when requesting IPv4 configuration through
DHCP 4o6.
The communication of parameters between the client and server is a
two-way process: OPTION_DHCP4O6_SADDR_HINT is optionally used by the
DHCP 4o6 server to indicate to the client a preferred IPv6 prefix for
binding the received IPv4 configuration and sourcing tunnel traffic.
This may be necessary if there are multiple IPv6 prefixes in use in
the customer network (e.g. ULAs), or if the specific IPv4-over-IPv6
transition mechanism requires the use of a particular prefix for any
reason. When the client has selected an IPv6 address to bind the
IPv4 configuration to, it passes the address back to the DHCP 4o6
server through OPTION_DHCP4O6_SADDR.
A softwire initiator also requires the IPv6 address of the border
router (i.e. softwire tunnel concentrator). In the dynamic mode, it
SHOULD acquire an IPv6 prefix of the BR through OPTION_BR_PREFIX.
Then the /128 border router address is constructed in the same manner
as described in [I-D.ietf-softwire-map], by concatenating the
OPTION_BR_PREFIX with IPv4 address and PSID.
To configure a softwire with DHCP 4o6, the DHCP client requests the
4o6 Server Address option using DHCPv6. If the DHCPv6 server
includes the DHCP 4o6 Server Address option in its response, then
DHCPv4 over DHCPv6 can be enabled, as in [RFC7341]. If the IPv6
source address of the client changes (such as IPv6 lease expiration,
etc.), the client follows the Section 9 of [RFC7341] to re-enable the
DHCPv4-over-DHCPv6 function.
5. IPv6/IPv4 Binding Message Flow
The following diagram shows the client/server message flow and how
the options defined in this document are used. In each step, the
relevant DHCPv4 message is given above the arrow and the relevant
options below the arrow. The DHCPv4 messages are encapsulated in
DHCPv4-query or DHCPv4-response messages, and those options are
included in the 'options' field of the DHCPv4-query or
DHCPv4-response message.
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DHCP 4o6 DHCP 4o6
Client Server
| DHCPDISCOVER (DHCPv4) |
Step 1 |----------------------------------------------------->|
| ORO with OPTION_BR_PREFIX, |
| OPTION_DHCP4O6_SADDR_HINT(DHCPv6) |
| |
| DHCPOFFER (DHCPv4) |
Step 2 |<-----------------------------------------------------|
| OPTION_BR_PREFIX, OPTION_DHCP4O6_SADDR_HINT |
| (cipv6-prefix-hint with service provider's |
| preferred prefix) (DHCPv6) |
| |
| DHCPREQUEST (DHCPv4) |
Step 3 |----------------------------------------------------->|
| OPTION_BR_PREFIX, |
| OPTION_DHCP4O6_SADDR (cipv6-bound-prefix with |
| client's bound /128 IPv6 address) (DHCPv6) |
| |
| DHCPACK (DHCPv4) |
Step 4 |<-----------------------------------------------------|
| OPTION_BR_PREFIX, |
| OPTION_DHCP4O6_SADDR (cipv6-bound-prefix with |
| client's bound /128 IPv6 prefix) (DHCPv6) |
| |
IPv6/IPv4 Binding Message Flow
A client attempting dynamic softwire configuration includes the
option code for OPTION_BR_PREFIX, OPTION_DHCP4O6_SADDR_HINT in the
DHCPv6 ORO in all DHCPv4-query messages it sends.
When a DHCP 4o6 Server replies with a DHCPOFFER message, it SHOULD
include an OPTION_BR_PREFIX. It MAY also include
OPTION_DHCP4O6_SADDR_HINT, which is used to indicate a preferred
prefix that the client should use to bind IPv4 configuration to. If
this option is received, the client MUST perform a longest prefix
match between cipv6-prefix-hint and all prefixes/addresses in use on
the device. If a match is found, the selected prefix MUST then be
used to bind the received IPv4 configuration to. If the client
doesn't receive OPTION_DHCP4O6_SADDR_HINT the client can select any
valid /128 IPv6 prefix to use.
OPTION_DHCP4O6_SADDR is used by the client to inform the DHCP 4o6
Server which IPv6 address the IPv4 configuration has been bound to.
The client MUST put the selected IPv6 address into this option and
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include it in the DHCPv4-response message when it sends the
DHCPREQUEST message.
6. DHCPv6 Options
6.1. DHCPv4 over DHCPv6 Source Address Hint Option
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_DHCP4O6_SADDR_HINT | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|cipv6-hintlen | |
+-+-+-+-+-+-+-+-+ cipv6-prefix-hint .
. (variable length) .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o option-code: OPTION_DHCP4O6_SADDR_HINT (TBA1)
o option-length: 1 + length of cipv6-prefix-hint, specified in
bytes.
o cipv6-hintlen: 8-bit field expressing the bit mask length of the
IPv6 prefix specified in cipv6-prefix-hint.
o cipv6-prefix-hint: The IPv6 prefix indicating the preferred prefix
for the client to bind the received IPv4 configuration to.
6.2. DHCPv4 over DHCPv6 Source Address Option
The format of DHCPv4 over DHCPv6 Source address option is defined as
follows:
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_DHCP4O6_SADDR | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ cipv6-src-address +
. (128 bits) .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o option-code: OPTION_DHCP4O6_SADDR (TBA2)
o option-length: 16.
o cipv6-src-address: The IPv6 address that the client has bound the
allocated IPv4 configuration to.
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6.3. Border Router Prefix Option
The format of Border Router Prefix option is defined as follows:
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_BR_PREFIX | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|br-prefix6-len | |
+-+-+-+-+-+-+-+-+ br-ipv6-prefix +
. (variable length) .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o ooption-code: OPTION_BR_PREFIX (TBA3)
o option-length: 1 + length of br-ipv6-prefix specified in bytes.
o br-prefix6-len: 8 bits long field expressing the length of the
IPv6 prefix specified in the br-ipv6-prefix field.
o br-ipv6-prefix: a variable length field specifying the IPv6
address or prefix for the border router. It SHOULD be /64 or
/128.
This option provisions the softwire initiator with an IPv6 prefix of
BR. If the prefix length is /128, the softwire initiator takes this
/128 IPv6 address as the BR's tunnel endpoint address. If the prefix
length is /64, the softwire initiator MUST create the BR's /128
tunnel endpoint address by concatenating that prefix, its IPv4
address and PSID. This is similar to the initiator creating its own
IPv6 tunnel endpoint address [I-D.ietf-softwire-map].
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix from the OPTION_BR_PREFIX |
| (64-bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Zero Padding | IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Addr cont. | PSID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Prefix from the OPTION_BR_PREFIX: The IPv6 prefix got from the
OPTION_BR_PREFIX.
o Padding: Padding (all zeros).
o IPv4 Address: Public IPv4 address allocated to the client
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o PSID: Port Set ID allocated to the client, left padded with zeros
to 16-bits. If no PSID is provisioned, all zeros.
7. Security Considerations
TBD
8. IANA Considerations
IANA is requested to allocate the DHCPv6 option codes:
OPTION_DHCP4O6_SADDR_HINT, OPTION_DHCP4O6_SADDR and OPTION_BR_PREFIX.
9. Acknowledgements
The authors would like to thank Ted Lemon and Lishan Li for their
contributions.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC7341] Sun, Q., Cui, Y., Siodelski, M., Krishnan, S., and I.
Farrer, "DHCPv4-over-DHCPv6 (DHCP 4o6) Transport", RFC
7341, August 2014.
10.2. Informative References
[I-D.farrer-softwire-br-multiendpoints]
Farrer, I. and Q. Sun, "Multiple Tunnel Endpoints on
Border Router", draft-farrer-softwire-br-multiendpoints-00
(work in progress), March 2015.
[I-D.ietf-softwire-lw4over6]
Cui, Y., Qiong, Q., Boucadair, M., Tsou, T., Lee, Y., and
I. Farrer, "Lightweight 4over6: An Extension to the DS-
Lite Architecture", draft-ietf-softwire-lw4over6-13 (work
in progress), November 2014.
[I-D.ietf-softwire-map]
Troan, O., Dec, W., Li, X., Bao, C., Matsushima, S.,
Murakami, T., and T. Taylor, "Mapping of Address and Port
with Encapsulation (MAP)", draft-ietf-softwire-map-13
(work in progress), March 2015.
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[I-D.ietf-softwire-map-dhcp]
Mrugalski, T., Troan, O., Farrer, I., Perreault, S., Dec,
W., Bao, C., Yeh, L., and X. Deng, "DHCPv6 Options for
configuration of Softwire Address and Port Mapped
Clients", draft-ietf-softwire-map-dhcp-12 (work in
progress), March 2015.
[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.
Authors' Addresses
Ian Farrer
Deutsche Telekom AG
CTO-ATI, Landgrabenweg 151
Bonn, NRW 53227
Germany
Email: ian.farrer@telekom.de
Qi Sun
Tsinghua University
Beijing 100084
P.R. China
Phone: +86-10-6278-5822
Email: sunqi.csnet.thu@gmail.com
Yong Cui
Tsinghua University
Beijing 100084
P.R. China
Phone: +86-10-6260-3059
Email: yong@csnet1.cs.tsinghua.edu.cn
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