Redistribution BGP - OSPF

• Turn off BGP sync
• Use confederations
• Use another IGP instead, eg EIGRP
• For BGP to synchronize with OSPF, the router IDs must match
• When redistributing BGP into OSPF, it writes AS_PATH of the router into external route tag field of OSPF type 5 LSA. However, when redistribute OSPF into BGP, BGP process doesn't automatically assume tag contains AS_PATH. Need to use "set as_path tag" or "set auto-tag"
• One of reasons routers to ignore paths is because of paths marked as "not synchronized" in the "show ip bgp " output. If BGP synchronization is enabled, 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
• When the RR passes BGP routes from one RR client to another, the BGP router id will be the first RR client but OSPF router id will be RR itself, so there will never be a match between them. the solutions to this are:
  • turn off sync on 2nd RR client.
  • use confederation to make 2nd RR client "ebgp" peering to prior RR
• BGP peers will ALWAYS trust eBGP routes
• If R2 and R3 are route-reflector clients of R1, ONLY when OSPF is the IGP, BGP routes originated on R2 will NEVER be seen as valid on R3 and vice-versa because:
  • BGP and OSPF router IDs are required to match for BGP routes to be seen as valid
  • BGP and OSPF router IDs will never match on R2 and R3 due to presence of the the R1 route-reflector between the iBGP peers.
• To allow redistribute iBGP into IGP, need to configure "bgp redistribute-internal".