North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical RE: router startup behavior
> the most likely cause would be one of: <items deleted for brevity> > (c) script used to configure router(s) adds a 'network' > statement prior to trimming route-filters Yeah, (c) seems most likely to me. Ratul, a script like this or some variant could cause what you are seeing: config-router# no neighbor <a> config-router# no neighbor <b> config-router# no neighbor <c> (script to rewrite filters executes) config-router# neighbor <a> remote-as <x> config-router# neighbor <a> remote-as <y> config-router# neighbor <a> remote-as <z> (sessions start coming up) config-router# neighbor <a> route-map <A> out config-router# neighbor <b> route-map <B> out config-router# neighbor <c> route-map <C> out config-router# Ctrl-Z # clear ip bgp external soft out Just guessing - you're seeing these events between midnight and 5 am? > At 01:10 PM 14/01/2002 -0800, Ratul Mahajan wrote: > > > >to the best of my knowledge, here is what is happening. > > > >1. router starts rebooting > >2. there are routes in the routing table, some of which are not to > >be announce according to filters > >3. bgp sessions comes up; the filters have not yet taken effect > >4. start announcing routes > >5. filters come up > >6. the router realizes that it made a mistake and withdraws > the routes not > >meant to be announced. > > > >i should also point out that all such incident are not 1000 > router. most > >of them are 20-50, but i have seen non-trivial number of > ~100 prefixes, > >and a couple more than that. > > > > -- ratul > > > >On Mon, 14 Jan 2002, Ratul Mahajan wrote: > > > > > > > > > > > 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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