Re: Re: problem at mae-west tonight?

[eautheme () BayNetworks com (Eural Authement)]

Rob,

In the OSPF community,we faced this same issue a few years back -- the issue
being that all members of a single subnet were not reachable either by design
or by error and fooling the listeners of the Designated Router (like the
route server) into thinking that the nexthops were really reachable. We felt
the pains of this especially over virtual circuit networks (Frame Relay,
SMDS, and ATM). Temporary workarounds were created.  The two better solutions
were:

1) Using recommendations in RFC1586,"Guidelines for Running OSPF Over Frame
Relay Networks".  

2) Using Point-MultiPoint (P-MP) OSPF which is in the latest Internet-Draft
of the revision to the RFC1583 (V2 OSPF Spec.).

I prefer the P-MP solution because it is an automatic mechanism  requiring
very little configuration on a network administrators part and keeps the
number of routing hops to a minimum. 

I vote for P-MP as a "Standard" solution for BGP-4 over discontiguous
networks.  I believe this concept was proposed on this mailing list a few
months back.  Now that ATM VCs are being used at NAPs with route servers,
you'll see more and more of these problems arising...especially at NAPs where
there isn't much coordination and cooperation in building and maintaining
these high speed, virtual connections. 

Eural Authement
Bay Networks
Professional Services


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>  The problem I have with the route server this evening is that I announce
> my routes to the route server, and my policy configuration in the route
server
> reflects that I peer with Netcom, and so the route server tells Netcom how
> to reach me. Unfortunately, packets leaving Netcom headed to me at layer 2
> are going into a black hole. To fix this, I've had to dump my peering with
> the route server entirely, so that Netcom is only seeing my routes from
AGIS
> (our transit provider) and not from the route server. Ugh. My fears about
> the route server not knowing the status of the layer 2 topology have come
true,
> and there's no way to fix this that doesn't involve manual intervention.
>
> -matthew kaufman
>  matthew () scruz net

Well, I run gated on a BSDI box for the Hooked MAE West router.  I'm
thinking about implementing a "pingnouse INTERVAL" option on the
peer/group commands in gated, so it will periodically ping next hops
received from the route servers and set the nouse bit if the nexthop
is unreachable.  Any better ideas?

It would be nice to come up with a good mechanism for doing 3rd party
keepalives that cisco and other router vendors would be willing to
implement.

Rob

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