Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!ucsd!ucbvax!NSIPO.ARC.NASA.GOV!medin
From: medin@NSIPO.ARC.NASA.GOV ("Milo S. Medin", NASA ARC NSI Project Office)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Serious Routing Problems
Message-ID: <9007311833.AA22548@nsipo.arc.nasa.gov>
Date: 31 Jul 90 18:33:13 GMT
References: <61620@bu.edu.bu.edu>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
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Kent, I'm a little confused here.  Line flapping should be fixed by
having hystersis in the up/down line protocol.  It's been our
experience that OSPF in our system reroutes completely after about 3 seconds 
on average after the dead link is detected.  OSPF has it's timers
set up in a way as to avoid link flap causing a lot of simultaneous 
LSP flooding, due to deliberate jitter in the timers (LSP's being flooded
from all the gateways connected to a down net).

As for link up/downs going on every few seconds, we haven't had
experience with that sort of situation, but in the case of a link
that flaps every couple of minutes, that seems to work fine.
Because link-state protocols flood the topology information, and then
the routers recompute the routing tables more or less in parallel,
convergence can happen very quickly, and you also can do without
the complicated holddowns and such needed to prevent route looping
in vector-distance protocols.   This should be true for any reasonably
well implemented link-state protocol.  It's just easy to do this
part right.  You can certainly screw up in other ways, but if
you want fast convergance, fast enough to avoid lining up hundreds
of user TCP connections against a wall and killing them in rapid
sucession, you really need to use a link-state protocol.  This is
one reason why noone has bothered to build a new vector distance
IGP in quite some time.  Even the new proprietary IGP's these days 
are link-state based...

BARRNET also runs OSPF now, and those guys can tell you more 
about how it's performance has been.  

					Thanks,
					   Milo