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Operations Area                                                 T. Chown
Internet-Draft                                 University of Southampton
Expires: April 19, 2004                                 October 20, 2003


     Use of VLANs for IPv4-IPv6 Coexistence in Enterprise Networks
                    draft-chown-v6ops-vlan-usage-00

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

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   This Internet-Draft will expire on April 19, 2004.

Copyright Notice

   Copyright (C) The Internet Society (2003). All Rights Reserved.

Abstract

   Ethernet VLANs are quite commonly used in enterprise networks for the
   purposes of traffic segregation.   This document describes how such
   VLANs can be readily used to deploy IPv6 networking in an enterprise,
   including the most likely scenario of subnets running IPv6 in
   parallel with the existing IPv4 subnets in the enterprise.   The IPv6
   connectivity to the enterprise may or may not enter the site via the
   same physical link.









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Internet-Draft    Use of VLANs for IPv4-IPv6 Coexistence in Enterprise Networks                                      October 2003


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Enabling IPv6 per subnet . . . . . . . . . . . . . . . . . . .  4
   2.1 One VLAN per router interface  . . . . . . . . . . . . . . . .  4
   2.2 Collapsed VLANs on a single interface  . . . . . . . . . . . .  4
   2.3 Congruent IPv4 and IPv6 subnets  . . . . . . . . . . . . . . .  4
   3.  Example VLAN topology  . . . . . . . . . . . . . . . . . . . .  6
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  7
   5.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  8
       Normative References . . . . . . . . . . . . . . . . . . . . .  9
       Author's Address . . . . . . . . . . . . . . . . . . . . . . .  9
       Intellectual Property and Copyright Statements . . . . . . . . 10






































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Internet-Draft    Use of VLANs for IPv4-IPv6 Coexistence in Enterprise Networks                                      October 2003


1. Introduction

   Ethernet VLANs are quite commonly used in enterprise networks for the
   purposes of traffic segregation.   This document describes how such
   VLANs can be readily used to deploy IPv6 networking in subnets in an
   enterprise, including the most likely scenario of subnets running
   IPv6 in parallel with the existing IPv4 subnets in the enterprise.

   The IEEE 802.1Q VLAN standard allows separate LANs to be implemented
   over a single bridged LAN, by inserting "Virtual LAN" tagging or
   membership information into Ethernet frames.   Hosts and switches
   that support VLANs effectively allow software-based reconfiguration
   of LANs through configuration of the tagging parameters.   The
   software control means it is possible to bring in VLANs from separate
   places in the infrastructure without having to physically alter the
   wiring between the LAN segments and the IPv6 router.

   Many IPv4 enterprise networks will utilise VLAN technology.  If such
   a site wishes to introduce IPv6, it may do so as described below, by
   "overlaying" IPv6 subnets onto existing IPv4 subnets, without needing
   any changes to the IPv4 configuration.

   The IPv6 connectivity to the enterprise may or may not enter the site
   via the same physical link.



























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2. Enabling IPv6 per subnet

   The precise method by which IPv6 would be "injected" into the
   existing IPv4 network is implementation specific.   The general
   principle is that the IPv6 router device (e.g. performing IPv6 Router
   Advertisements [1] in the case of stateless autoconfiguration) is
   connected to the target subnet through the use of VLAN capable Layer
   2 equipment.

2.1 One VLAN per router interface

   In one case, an IPv6 router could be set up with an external
   interface connecting to the wider IPv6 internet, and any number of
   (IPv6-only) interfaces facing the internal network.   The external
   interface may be dual-stack if some tunnel mechanism is used for
   external connectivity, or IPv6-only if a native connection is
   available.

   By connecting the internal interfaces directly to a VLAN-capable
   switch, VLAN tagging on each port of that switch can be used to
   create virtual LANs that will carry that traffic internally to IPv6
   subnets that may be dispered widely across the internal network.

   The internal facing interfaces on the IPv6 edge router may feed other
   IPv6 routers over IPv6-only links which in turn inject the IPv6
   connectivity (the /64 subnets and associated Router Advertisements)
   into the VLANs.

   It is not necessary to do VLAN tagging in all cases. On some Layer 3
   switches, IPv6 traffic can directly be distributed to specific ports
   by adding them to the same protocol-based VLAN (in this case
   IPv6-based VLANs).

2.2 Collapsed VLANs on a single interface

   Many devices now support VLAN tagging based on virtual interfaces
   such that multiple IPv6 VLANs could be assigned from one physical
   router interface port.   Thus it is possible to use just one router
   interface for "aggregated" VLAN trunking from a switch.

2.3 Congruent IPv4 and IPv6 subnets

   The VLAN technology can be used to deploy IPv6-only VLANs in an
   enterprise network.   However most enterprises will be interested in
   dual-stack IPv4-IPv6 networking in the early stages of IPv6
   deployment.

   In such a case the IPv6 connectivity may be injected into the



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   existing IPv4 VLANs, such that the IPv4 and IPv6 subnets or links are
   congruent (i.e. they coincide exactly when superimposed).   Such a
   method may have desirable administrative properties, e.g. the devices
   in each IPv4 subnet will be in the same IPv6 subnets also.

   Further, IPv6-only devices may be gradually added into the subnet
   without any need to resize the IPv6 subnet (which may hold in effect
   an infinite number of hosts in a /64 in contrast to IPv4 where the
   subnet size is often relatively limited). The lack of requirement to
   periodically resize an IPv6 subnet is a useful administrative
   advantage.








































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Internet-Draft    Use of VLANs for IPv4-IPv6 Coexistence in Enterprise Networks                                      October 2003


3. Example VLAN topology

   The following figure shows how a VLAN topology may be used to
   introduce IPv6 in an enterprise network.


   (Subnet1) (Subnet2) (SubnetN)
        \     /            |
       [Switch1]       [SwitchN]
           \             /
            \           /
    ( VLAN infrastructure in the enterprise )
                  |
     [ Ethernet switch with VLAN support ]
                  |
          FE/GE w/ VLAN tagging
            [ IPv6-router ]
                  |
   ( connections to other IPv6 routers or the Internet )
     ( also possibly the IPv4 connectivity )


   Figure 1: IPv6 deployment using VLANs




























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4. Security Considerations

   There are no additional security considerations particular to this
   method of enabling IPv6 on a subnet.

   Where the IPv6 connectivity is delivered into the enterprise network
   by a different path from the IPv4 connectivity, care should be given
   that equivalent application of security policy (e.g. firewalling) is
   made to the IPv6 path.










































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5. Acknowledgements

   The author would like to thank colleagues on the 6NET project, where
   this technique for IPv4-IPv6 coexistence is widely deployed,
   including Janos Mohacsi (Hungarnet), Martin Dunmore and Chris Edwards
   (Lancaster University), Christian Strauf (JOIN Project, University of
   Muenster), Stig Venaas (UNINETT) and Pekka Savola (CSC/FUNET).












































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Normative References

   [1]  Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery for
        IP Version 6 (IPv6)", RFC 2461, December 1998.


Author's Address

   Tim Chown
   University of Southampton

   Southampton, Hampshire  SO17 1BJ
   United Kingdom

   EMail: tjc@ecs.soton.ac.uk




































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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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Acknowledgment

   Funding for the RFC Editor function is currently provided by the
   Internet Society.











































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