Re: ping-pong phenomenon with p2p links & /127 prefixes

["t.petch" <ietfc@btconnect.com>]

---- Original Message -----
From: "Ole Troan" <ot@cisco.com>
To: "Seiichi Kawamura" <kawamucho@mesh.ad.jp>
Cc: <v6ops@ops.ietf.org>; <ipv6@ietf.org>
Sent: Tuesday, August 17, 2010 12:02 PM

> Seiichi-san,
>
> >> BGP peerings and what not could use link-local addresses. e.g:
> >>
> >> router A --------------  router B
> >> fe80::1                        fe80::2
> >> dead:beef::1/128     c001:cafe::2/128
> >
> > if
> >   I get a BGP neighbor down message with fe80::2
> > then
> >   what address do I ping, trace? I can look at config of router A
> >   and my address is dead:beef::1. What's the other side's global address?
> >   If router B isn't mine, I may not have a clue.
> >
> > The challenge here is that we don't always have the knowledge of
> > whats on the other side of the router. When you have tons of these
> > links on one router, this is just making trouble shooting harder.
> >
> > Even if I did know the other side's global address, monitoring pings
> > cannot be sent to fe80::2. We'll have to ping c001:cafe::2 and
> > manually link that status with fe80::2 peering session on the NMS.
> > I would hate to do that with hundreds of sessions running inside my network.
> > That's always been a causes mistakes. We want to monitor what's
> > acutally running and not some alias address.
>
> yes, I see that point.
> how do you troubleshoot when you get a OSPFv3, RIP, or ISIS neighbor down
message?
> cause then you'd only have a link-local address or a CLNS address. or is BGP
troubleshooting different in some way?

I would stress that OSPF (eg) and BGP are different animals.

With BGP, a boundary runs through the middle of a link, the two ends (at least
of eBGP) belong to different administrations with, likely, different views of
how to operate a network, potentially different equipment manufacturers etc.
(Adherence to RFC matters more:-)

With OSPF etc, a boundary, such as there is one, runs through the middle of a
router, the link is all in one part (area, domain ...) and so the administration
of the two ends is closely linked and operations can be too.  Mostly there will
be common operations, naming standards etc for the whole OSPF domain.

The two are quite different to manage.

Tom Petch

>
> this is a solvable problem. it could be done through a management system,
better support in routers, a script pinging the link-local address from the
router, and I'm sure lots of other solutions.
>
> I'm trying to understand if this is "just" resistance to change (yeah, I know
both too little and too much got changed with IPv6.) with the argument being
that "this is how we have done it for the last 20 years and we will continue to
do it this way whatever argument you make", or if there are real technical and
operational issues with link-local only (optionally with /128) p2p links.
>
> we as the IETF community need operator input and we need to understand
operational complexities. thanks for replying.
> (and perhaps even Randy with his ever so charming ways also think so.)
>
> cheers,
> Ole
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