Network Working Group S. Daniel Park
Internet Draft P. Kim
Expires : October 20, 2004 Samsung Electronics
April 19, 2004
DHCP Option for Configuring IPv6-over-IPv4 Tunnels
<draft-daniel-dhc-ipv6in4-opt-03.txt>
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Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This document provides a mechanism by which the DHCPv4 servers can
provide information about the configured IPv6-over-IPv4 tunnel
end-point. The IPv4/IPv6 dual-stack nodes can use this
information to set up a configured tunnel to the tunnel end-point
to obtain IPv6 connectivity.
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Table of Contents
1. Introduction.................................................2
2. Requirements.................................................2
3. Configured Tunnel End Point Option...........................3
4. Multiple Tunnel End Point Considerations.....................3
5. Security Considerations......................................4
6. Extended Usage...............................................4
7. IANA Considerations..........................................5
8. References...................................................5
8.1 Normative References....................................5
8.2 Informative Reference...................................5
9. Authors' Addresses...........................................6
10. Acknowledgements.............................................6
1. Introduction
In the initial deployment of IPv6, the IPv6 nodes may need to
communicate with the other IPv6 nodes via IPv4 tunnel service. The
connectivity can be obtained by setting up an IPv6-over-IPv4
configured tunnel between a client and a tunnel router.
This document defines a new option by which the DHCPv4 [RFC-2131]
server can notify the client with the list of end-points of the
possible configured tunnels.
Particularly, this mechanism is useful where the ISP is providing
the IPv6 services but is doing it using tunneling over IPv4 to avoid
upgrading all their infrastructure to support IPv6 on day one.
Regarding IPv6-over-IPv4 tunnel, the tunnel broker [RFC-3053]
architecture has been widely deployed in the dual networks to obtain
IPv6 connectivity via tunnel service because of easy configuration
on the users. After configuring IPv6-over-IPv4 tunnel between the
users and the selected tunnel server, tunnel broker allows user to
get access to the 6bone or any other IPv6 network the tunnel server
is connected to. In case of no tunnel broker, the proposed
mechanism in this document can allow users to obtain the IPv6
connectivity efficiently.
2. Requirements
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The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
document, are to be interpreted as described in RFC 2119 [RFC-2119].
3. Configured Tunnel End Point Option
This option specifies the configured tunnel end-point that client
should use when discovering the IPv4 address of the ISP's tunnel
router somehow via the Dynamic Host Configuration Protocol.
Once the IPv4 address has been learned, it is configured as the
tunnel end-point for the configured IPv6-over-IPv4 tunnel.
The format of the Configured Tunnel End Point Option is shown as
below;
The code for this option is TBD. The length of this option is 4.
Code Length CTEP Order in Sequence
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_CTEP | Len | CTEP Addr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CTEP Addr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
In the above diagram, CTEP Addr is 32-bit integers corresponding to
DHCP options which specify the IP address of different configured
tunnel end-point.
As described in [RFC-2893], the dual node received CTEP option MUST
store the tunnel end-point address and this address is used as
destination address for the encapsulating IPv4 header.
The determination of which packets to tunnel is usually made by
routing information on the encapsulator. This is usually done via a
routing table, which directs packets based on their destination
address using the prefix mask and match technique. For more
information, refer to section 4. Configured Tunneling in [RFC-2893].
4. Multiple Tunnel End Point Considerations
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For the simple configured tunnel, one tunnel end-point is generally
used and it assumes that all the networks will be reached through
the same end-point. In this case, one CTEP Addr field in the CTEP
option is used for configured tunnel service.
The list of end-points can be installed as the default routes and
the routes will be tried in a round robin fashion if the IPv6 host
load-sharing is honored [IPv6LOAD]. Instead there can be specific
default routes for the different destination.
Generally, there may not be a need for installing multiple
configured tunnel end-points unless administrator wants two for
redundancy purposes. It is out of scope of this draft.
5. Security Considerations
A rouge DHCP server can issue invalid or incorrect configured tunnel
end-point. This may cause denial of service due to unreachability
or makes the client to reach incorrect destination.
The latter has very severe security issues as the tunnel end-point
is on-the-path towards all the IPv6 destinations, and can trivially
act as a man-in-the-middle attacker.
To increase secure exchange between users and tunnel end-points, the
tunnel broker or any tunnel agent can be used for configuring IPv6-
over-IPv4 tunnels including authentication, security association and
so on, but it is not scope of this document.
The authenticated DHCP [RFC-3118] can be also used for secure
exchange between users and tunnel end-points (routers).
6. Extended Usage
As stated in Introduction, the tunnel broker is a nice tool for
allowing user to get the IPv6 connectivity through IPv6-over-IPv4
tunnel. To configure tunnel between users and tunnel servers, users
have to access to the tunnel broker by web registration and then
tunnel broker set up tunnel between users and a selected tunnel
server. Prior to filling up the form on the tunnel broker, users
have to know the IPv4 address of the tunnel broker (as described in
[6], it may be IPv6 addressable but not mandatory). Regarding this
operation, this option proposed in this document can allow users to
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obtain an available tunnel broker address (or addresses) without any
manual operations.
For this operation, a new option (called Tunnel Broker Configuration
Option: option name is OPTION_TBCO and value is TBD) can be simply
made by DHCPv4 option extension which may be the same format as CTEP
option.
To increase secure exchange between users and tunnel end-points
(tunnel servers or dual routers) this extended usage can be applied
for configuring IPv6-over-IPv4 tunnel instead of direct tunnel
configuration between them. Specific method for secure exchange is
beyond scope of this document.
7. IANA Considerations
IANA is requested to an assign value for the Configured Tunnel End
Point option code in accordance with RFC 2939 [RFC-2939].
Option Name Value Described in
OPTION_CTEP TBD Section 3.
8. References
8.1 Normative References
[RFC-2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
2131, Bucknell University, March 1997.
[RFC-2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC-2939] Droms, R.,"Procedures and IANA Guidelines for Definition
of New DHCP Options and Message Types", RFC 2939,
September 2000.
[RFC-3118] Droms, R., "Authentication for DHCP Messages", RFC 3118,
June 2001.
8.2 Informative Reference
[RFC-2893] Nordmark, E. and Gilligan, R.E., "Basic Transition
Mechanisms for IPv6 Hosts and Routers", RFC 2893, August
2000.
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[IPv6LOAD] Hinden B. and Thaler D., "IPv6 Host to Router Load
Sharing", Internet-Draft (work in progress), January
2004.
[RFC-3053] Durand, A., ôIPv6 Tunnel Brokerö, RFC 3053, January
2001.
9. Authors' Addresses
Soohong Daniel Park
Mobile Platform Laboratory
Samsung Electronics.
Suwon
Korea
Phone: +81 31 200 4508
Email: soohong.park@samsung.com
Pyungsoo Kim
Mobile Platform Laboratory
Samsung Electronics.
Suwon
Korea
Phone: +81 31 200 4635
Email: kimps@samsung.com
10. Acknowledgements
Special thanks to Pekka Savola, Vijayabhaskar A K, Eric Nordmark and
Alain Durand for their many valuable revisions and comments. In
particular, Pekka Savola kindly clarified the multiple tunnel end
point considerations with his good experience as well.
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