Hi Karl, I posted this on the CCIE board the other day, might be useful for yourself.
Also want to note that the 'no sych' command is required if you are using OSPF, since there is a extra requirement that the OSPF route and BGP route have to be sourced from the same router-id. Take a look at the below CCO info. http://www.cisco.com/warp/customer/459/25.shtml 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. Regards, Albert CCIE #8705 -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Karl Brusen Sent: Tuesday, September 10, 2002 11:16 PM To: [EMAIL PROTECTED] Subject: BGP/OSPF Synchronization [7:52980] Can anyone point me towards a resource that describes in detail what it takes for BGP to consider a route synchronized when it learned it through IGP OSPF? My study partner and I are struggling understanding how it works. All of our resources provide only general information with statements like, "a route must be learned by IGP before BGP will consider it synchronized". Merely learning a route from IGP is apparently not good enough. There must be other, more specific requirements. How does route-reflection affect BGP/OSPF synchronization? Specifically, we are working on a lab with three routers running BGP. They are in the same AS (IBGP). They are not fully meshed one is acting as a router reflector for the other two. One of the RR clients has a loopback injected into BGP by redistribute connected. All three routers are also running OSPF and have an IGP route to the same network being injected into BGP. The route is synchronized on the router it is injected into and on the route reflector, but it isn't synchronized on the other route reflector client. We are aware of how BGP and OSPF router IDs can prevent synchronization, so we have specified the same router IDs for BGP and OSPF. What is interesting is that if we point a static route from the problem route-reflector client to the BGP route "next hop", BGP synchs. Due to the network topology and modifications of the ad distance, the problem router also has a route learned from EIGRP but is not normally in the IP routing table. When we shut down an interface so that the EIGRP route is placed in the IP routing table, BGP synchs. We are very confused. There is something about how BGP synchs with OSPF that we just don't understand. Any insight from the group will be greatly appreciated. Thanks, Karl Brusen Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=53061&t=52980 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
