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.
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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.
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regards
Mukesh
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Mukesh Gupta
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http://www.iprg.nokia.com/~mgupta
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