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North American Network Operators Group

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router startup behavior

  • From: Ratul Mahajan
  • Date: Mon Jan 14 13:56:25 2002


at university of washington, we are doing a measurement study of bgp
misconfiguration
(http://www.cs.washington.edu/homes/ratul/bgp/index.html).  

one of the things we found is that there are a lot of announcements of
more-specifics that come and go within a matter of 2-5 minutes.

by talking to the operators involved in these incidents, we found that
most of these are caused when the router is rebooted (intentionally or
not). while some operators were aware of this side effect, most were not,
and were taken by surprise that they just injected anywhere from 1-1000
routes into BGP only to withdraw them a couple of minutes later.

i would like to understand this behavior better. is this behavior
vendor-specific (cisco?) or pervasive? is there a configuration style that
causes or avoids this "spill-over"?

my understanding is limited to this happens when the bgp session comes up
too soon, before the filters have taken effect. could someone familiar
with router internals shed some light on it?

the problem is limited to route origination only, or also propagation?  
in other words, can a router propagate a route it should not while
starting up because export filters are not yet in place?

never ever gotten my hands dirty into router configuration; your input 
would be invaluable.

thanks,
	-- ratul






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