Subject: Calculating link local for IPv6 in IPv6 tunnels

From: Mukesh Gupta <[email-masked]>
Date: Wed, 06 Nov 2002 17:34:23 -0800

Hi All,

Last paragraph of Appendix A in RFC 2373 (IPv6 Addressing Architecture)
suggests various methods for creating a unique link local address for
tunnel interfaces. The RFC suggests that the implementors can choose any

algorithm as long as it meets the requirements.

I am implementing IPv6 in IPv6 tunnels (RFC 2473) and I wanted to know
how other implementations are generating the unique link local address
so that I can minimize the chances of collision by using the same
algorithm. Any information would be highly appreciated.

-------------------------------------------------------------------
Links without Identifiers

   There are a number of links that do not have any type of built-in
   identifier.  The most common of these are serial links and configured

   tunnels.  Interface identifiers must be chosen that are unique for
   the link.

   When no built-in identifier is available on a link the preferred
   approach is to use a global interface identifier from another
   interface or one which is assigned to the node itself.  To use this
   approach no other interface connecting the same node to the same link

   may use the same identifier.

   If there is no global interface identifier available for use on the
   link the implementation needs to create a local scope interface
   identifier.  The only requirement is that it be unique on the link.
   There are many possible approaches to select a link-unique interface
   identifier.  They include:

      Manual Configuration
      Generated Random Number
      Node Serial Number (or other node-specific token)

   The link-unique interface identifier should be generated in a manner
   that it does not change after a reboot of a node or if interfaces are

   added or deleted from the node.

   The selection of the appropriate algorithm is link and implementation

   dependent.  The details on forming interface identifiers are defined
   in the appropriate "IPv6 over <link>" specification.  It is strongly
   recommended that a collision detection algorithm be implemented as
   part of any automatic algorithm.
-------------------------------------------------------------------

regards
Mukesh

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