ipv6 next-hop link-local

Gert Doering gert at space.net
Sun Feb 20 10:36:13 CET 2011


On Sun, Feb 20, 2011 at 10:35:50AM +1030, Mark Smith wrote:
> > There's a fair bit of operational experience on the routing side of things
> > (the IXPs we're connected to have offered IPv6 roughly since 2001).
> I just wonder if those sorts of deployments have followed "IPv4
> thinking". I think "IPv4 thinking" is "this is how we can do it and do
> do it in IPv4, so we'll do it the same way in IPv6, because IPv6 is
> similar enough to IPv4."

Well, partly it's "IPv4 thinking", of course.  OTOH, in certain areas,
"IPv4 thinking" has gained 15+ years of experience in doing things since
IPv6 was designed, and just because it's IPv4, it doesn't have to be

Specifically the topic at hand, using link-locals at an IXP, has some
benefits - and at the same time, serious operational drawbacks, like 
"monitoring your eBGP peers in your NMS by IPv6 address" - now which 
of the two IXPs I'm connected to is the fe80::ab:cd neighbour that just 
went down?

I've seen so much operational problems due to, well, inexperienced 
router operators (or just "fat fingers") that anything that requires
extra thinking or has the potential for extra breakage is something
I see with certain doubts.

> I get concerned about people lobbying for removal of IPv6 features when
> they seem to be doing it from an "IPv4 thinking" perspective. 

I'm actually not lobbying to take away the configuration option of
consciously using link-local addresses - give people enough rope, etc. -
(and I earn my living by fixing other people's networks).

What I'm lobbying for is what Juniper already does: on an eBGP session
that's established between global addresses, do not install the link-local
next-hop in the FIB, but use the global next-hop.

Specifically, always use the scope of the eBGP endpoint address to
decide upon the scope of the next-hop being used.

Using link-local next-hops on an eBGP session established between
directly connected neighbours on an IXP using global addresses for
the endpoints has a strong smell of "too much IPv6 thinking" to me, 
bringing extra pitfalls with no benefits that I can see (maybe I'm 
overlooking something).

Gert Doering
        -- NetMaster
did you enable IPv6 on something today...?

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