> Drew Weaver > Sent: Thursday, October 8, 2020 2:01 PM > What I expect to happen is: > > The route to the peering edge router's loopback interface is > withdrawn when OSPF/OSPFv3 closes. > The core router will close the BGP session when the route to the dead > peering edge router is withdrawn and will begin using one of the 5 other > copies of the same route that it has. >
Number of things come to mind since you provided no details regarding the setup Case A) If all 5 peering points are not advertising best-external prefixes -then there's only a single path for each of the 700K prefixes in the entire AS via one of the 5 peering points. -in case one peering point fails all prefixes it offered a best path for will be withdrawn from all BGP speakers in the AS at OSPF convergence speeds, but then the remaining 4 peering points needs to realize they now have the overall best path for a given prefix and start advertising it to all BGP speakers in the AS -tedious process that converges at "BGP-speed". Case B) If all 5 peering points are advertising best-external prefixes and all BGP speakers in the AS already have all 5 paths available in RIB, but none of the BGP speakers has hierarchical FIB so there's a direct correlation between a prefix and it's NH, -in case one peering point fails all prefixes it offered a best path for will be withdrawn from all BGP speakers in the AS at OSPF convergence speeds, but now each BGP speaker will need to painstakingly update its FIB on a prefix by prefix bases for each of the each of the 700K prefixes. Case C) If all 5 peering points are advertising best-external prefixes and all BGP speakers in the AS already have all 5 paths available in RIB, and all BGP speakers not even have hierarchical FIBs but also PIC-CORE enabled where a backup path for each prefix is programmed in FIB, -in case one peering point fails all prefixes it offered a best path for will be withdrawn from all BGP speakers in the AS at OSPF convergence speeds and each BGP speaker will then just need to change 5 HN pointers to point to remaining 4 peering points in FIB. Note, The above assumes full mesh between all BGP speakers or otherwise assumes the RR infrastructure emulates full-mesh with regards to prefix distribution to all BGP speakers in the AS via one of the several available mechanisms. Adam _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
