ipv6 next-hop link-local

Mark Smith nanog at 85d5b20a518b8f6864949bd940457dc124746ddc.nosense.org
Sat Feb 19 11:01:29 CET 2011

On Sat, 19 Feb 2011 10:41:22 +0100
Gert Doering <gert at space.net> wrote:

> Hi,
> On Fri, Feb 18, 2011 at 11:08:13PM +0100, Francis Dupont wrote:
> >    I think both the RFC and the Cisco implementation are stupid, because
> > 
> After reading the RFC two more times, I seem to understand where the
> initial idea comes from - networks that share eBGP routers and "other
> stuff", and where you want to send ICMP redirects and/or RIPng updates
> with a next-hop pointing to "other routers".
> Our operational problems come from networks that only have eBGP 
> speakers - namely, exchange point meshes - and link-local next-hops
> have no reason for existance there.  No RIPng, no ICMP redirects.

I think they can have a place there. If your exchange point eBGP
routers "next-hop self" when they distribute routes into iBGP, then the
eBGP next hops are only visible to the eBGP router. Using link locals
(static link locals if you like) for that can provide the benefit of
making you eBGP relationships independent of the global addressing that
is being used on the exchange point mesh. 

> So what I would have wished for is some strong words in this RFC
> that discourage use of received link-local next-hop, unless other
> protocols are in use that require them.  Or something that would
> encourage router vendors to add a switch to their implementation 
> to give the network admin the choice...
> (Basically, this is what I hoped to find in the Cisco BGP implementation
> - a switch like "neighbour 2001:db8::1 always-use-global-nexhop", but that
> one doesn't exist)


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