Kevin Dorrell, CCIE #20765

23 Feb 2008

IPv6 BGP : Peering across link-local addresses

Filed under: IPv6 — dorreke @ 17:56

I just learned that you can peer IPv6 BGP across link-local addresses, even on a tunnel interface.  This came as a surprise to me.  I had always peered across site local addresses and I had assumed that you could not peer across link-local addresses because they are not unique.

(OTOH, I should not have been surprised.  After all, IPv6 OSPF can form adjacencies across link-local addresses, so why not BGP).

So, if you are going to peer to, say, fe80::5, how does the router know which interface to connect through?  Wel, in the example in this lab, we specify the update source too, so I am guessing that it uses that to determine which interface to connect through.

This has some strange implications.  Suppose you have two link-neighbors, but they both have the address fe80::2.  You can only peer with one of them.  For the other one, you would have to use a unique address.

Futhermore,  if your neighbor is a link-local address, then the update source must be mandatory.

The wierd and wonderful world of IP6!

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1 Comment »

  1. hi Kevin,
    i have a basic doubts in ipv6 understanding.
    1.I had always peered across site local addresses and I had assumed that you could not peer across link-local addresses because they are not unique.
    —> Link local addressess are derived from MAC, then how it is possible to being not unique?
    i think this is very basic.as i am a fresh graduate i dont know ?
    by,
    saravan prabu p

    Comment by saravan prabu — 19 Jan 2011 @ 12:42


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