BGP-OSPF interaction has specifically been made Historic by the IETF (i.e., obsolete). It's not in the current BGP documents, and there is an administrative document that obsoletes 1364.
Sounds like Cisco meets the old RFC 1364, but new implementations won't have the restriction. >reflectors. > >The requirement for the BGP/OSPF identifier is stated in RFC 1364: > >"Varadhan [Page >4] > >RFC 1364 BGP OSPF Interaction September 1992 > > >3. BGP Identifier and OSPF router ID > > The BGP identifier must be the same as the OSPF router id at all > times that the router is up. > > This characteristic is required for two reasons. > > i. Consider the scenario in which 3 routers, RT1, RT2, and RT3, > belong to the same autonomous system. > > +-----+ > | RT3 | > +-----+ > | > > Autonomous System running OSPF > > / \ > +-----+ +-----+ > | RT1 | | RT2 | > +-----+ +-----+ > > Both RT1 and RT2 have routes to an external network X and import it > into the OSPF routing domain. RT3 is advertising the route to > network X to other external BGP speakers. RT3 must use the OSPF > router ID to determine whether it is using RT1 or RT2 to forward > packets to network X and hence build the correct AS_PATH to advertise > to other external speakers. > > More precisely, RT3 must use the AS_PATH of the route announced by > the ASBR, whose BGP Identifier is the same as the OSPF routerID > corresponding to its route for network X. > > ii. It will be convenient for the network administrator looking >at > an ASBR to correlate different BGP and OSPF routes based on > the identifier." > > >Cisco issued a field notice on the problem where there was a route >reflector. (Can't locate it in my pile(s)) > >In One Tech Note (BGP Best Path Selection Algorithm): > >"Paths marked as "not synchronized" in the show ip bgp >output. If BGP synchronization is enabled, which it is by default in >Cisco IOS. Software, there must be a match for the prefix in the IP >routing table in order for an internal (iBGP) path to be considered a >valid path. If the matching route is learned from an OSPF neighbor, its >OSPF router ID must match the BGP router ID of the iBGP neighbor. Most >users prefer to disable synchronization using the no synchronization BGP >subcommand." > >The comparison can be done using the sh ip bgp xxx.yyy.zzz.aaa and show >ip ospf data. > >HTH, Fred. > >John Neiberger wrote: >> >> We discovered something on the CCIE list recently and I'm >> wondering if anyone might be able to explain the reasoning >> behing this behavior. >> >> BGP synchronization rules require that if an iBGP peer is to >> advertise a route learned via iBGP, it must have that prefix >> *and* the next hop for that route in the routing table already. >> >> An interesting added complexity to this occurs if your IGP is >> OSPF. If the router in question has learned these prefixes via >> OSPF, then the advertising router ID in the OSPF database must >> match the router ID of the iBGP peer that advertised the route. >> >> Has this behavior caused any problems for any of you? Do you >> know why the synchronization rules have a special case for OSPF >> and not other routing protocols? >> >> I was working with someone else on a practice lab and we ran >> into this issue. We were both going nuts trying to figure out >> why the iBGP routes weren't synchronizing and this turned out >> to be the cause. >> >> Any thoughts? >> >> Thanks, >> John >> >> ________________________________________________ >> Get your own "800" number >> Voicemail, fax, email, and a lot more >> http://www.ureach.com/reg/tag Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=30367&t=30126 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
