bgpd: fix consider in NHT BGP update with same prefix/nexthop #17428
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All BGP configuration do not consider any BGP updates which have the same prefix and nexthop. Example: > p2# show bgp ipv4 > BGP table version is 2, local router ID is 198.51.100.3, vrf id 0 > Default local pref 100, local AS 65500 > Status codes: s suppressed, d damped, h history, * valid, > best, = multipath, > i internal, r RIB-failure, S Stale, R Removed > Nexthop codes: @NNN nexthop's vrf id, < announce-nh-self > Origin codes: i - IGP, e - EGP, ? - incomplete > RPKI validation codes: V valid, I invalid, N Not found > > Network Next Hop Metric LocPrf Weight Path > i198.51.100.5/32 198.51.100.5 0 100 0 i The consequence is that this BGP update is not considered as reachable, and is not redistributed. This is an issue on a Route Reflector case. The previous fix prevented from handling this kind of update; testing the reachability of such nexthop would lead in a loop, from routing perspective. In reality, that BGP update is frequently used in networks, today. Fix this by considering the BGP update, only if there is an existing bnc entry. Signed-off-by: Philippe Guibert <[email protected]>
ton31337
reviewed
Nov 14, 2024
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Can you give me examples of when a prefix and the same nexthop are allowed and not allowed? I'm a bit confused about what this is now. |
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This is something like: 198.51.100.5 (iBGP neighbor), which is usually accessible via IGP(not BGP?), so there might be a case. |
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All BGP configuration do not consider any BGP updates which have the same prefix and nexthop. Example:
The consequence is that this BGP update is not considered as reachable, and is not redistributed. This is an issue on a Route Reflector case.
The previous fix prevented from handling this kind of update; testing the reachability of such nexthop would lead in a loop, from routing perspective. In reality, that BGP update is frequently used in networks, today.
Fix this by considering the BGP update, only if there is an existing bnc entry.