North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: BGP route update propagation questions
I know that at least one vendor had a bug whereby when bestpath changed and the med also changed it did not always propogate the med change. - jared s74182 On Tue, Apr 16, 2002 at 08:11:41PM -0400, David G. Andersen wrote: > > I'm trying to get a better feel for the dynamics of some > "maybe-necessary" BGP routing traffic, and had a few questions: > > Under what circumstances will BGP send an update (of any sort) > to a peer when there is an internal failure that does _not_ > result in the complete isolation of a prefix? > > For example: > > __ AS1-rtr1 ---*-- AS2-rtr1 --\ > / | -- AS3 > 10/8 -X- AS1-rtr2 ---*-- AS2-rtr2 --/ > ^ > |--link goes down at X > > In this case, AS1 is announcing 10/8 to its peer, AS2. > An internal link within AS1 goes down. Are there any > circumstances under which AS2 will announce some kind of > change to AS3? My thoughts: > > * AS1 might announce a MED change to AS2, and AS2 might > propagate that to AS3 in some unknown way (manually?) > * AS2 would see the path to AS1 change, and would change > its announced MED accordingly > * For some reason, AS1 might announce a withdraw on 10/8, > and then re-announce it. Is this possible, and under > what circumstances would this happen? > * Other things? I feel like the answers might depend on > networks using ibgp with route reflectors vs. full mesh, > or using a different interior routing protocol. > > In a related situation, let's say AS1 did a 'clear ip bgp' > on AS1-rtr2, which was the preferred link for AS2 to get to 10/8. > Would AS2 propagate any internal BGP announcements to AS3? > (Same kinds of reasons as above, but this time AS1-rtr2 > actually stopped announcing anything to AS2) > > I'm not certain of the right framework in which to think about > the answers to these questions, alas. Clues from the operational > side would be very welcome indeed. > > -Dave > > -- > work: [email protected] me: [email protected] > MIT Laboratory for Computer Science http://www.angio.net/ -- Jared Mauch | pgp key available via finger from [email protected] clue++; | http://puck.nether.net/~jared/ My statements are only mine.
|