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bgpd: nht unresolved with global address next-hop (backport #8958) #9142

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merged 1 commit into from
Jul 23, 2021

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@mergify mergify bot commented Jul 23, 2021

This is an automatic backport of pull request #8958 done by Mergify.


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When bgp peers with ipv6 link local addresses, it may receive a
BGP update with next-hop containing both LL and GA information.
By default, nexthop tracking applies to GA, and ignores presence
of LL, when both addresses are present. This is a problem for
resolving GA as next-hop as the next-hop information can be solved
by using the LL address only.

The solution consists in defaulting the nexthop ipv6 choice to LL
when available, and moving back to GA if a route-map is locally
configured at inbound.

Signed-off-by: Philippe Guibert <[email protected]>
(cherry picked from commit 17ef5a9)
@polychaeta polychaeta added the bgp label Jul 23, 2021
@donaldsharp donaldsharp merged commit f3134b8 into stable/8.0 Jul 23, 2021
@mergify mergify bot deleted the mergify/bp/stable/8.0/pr-8958 branch July 23, 2021 12:31
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Continuous Integration Result: SUCCESSFUL

Congratulations, this patch passed basic tests

Tested-by: NetDEF / OpenSourceRouting.org CI System

CI System Testrun URL: https://ci1.netdef.org/browse/FRR-FRRPULLREQ-20458/

This is a comment from an automated CI system.
For questions and feedback in regards to this CI system, please feel free to email
Martin Winter - mwinter (at) opensourcerouting.org.

@tobias-urdin
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Does anybody know if this is in the released version 8.0 or just backported for a next 8.0 minor release?

@tobias-urdin
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tobias-urdin commented Aug 18, 2021

The reason I ask is because I can't see it making the correct NHT decision based on this commit when running FRR package 8.0-0~ubuntu20.04.1 on Ubuntu 20.04

rr# show bgp 2c0f:fff0::/32
BGP routing table entry for 2c0f:fff0::/32, version 0
Paths: (1 available, no best path)
  Not advertised to any peer
  174 3741 30988 37125, (Received from a RR-client)
    2001:978:2:6f::47:1 (inaccessible) from 10.255.4.101 (10.255.0.101)
    (fe80::b696:91ff:fea6:9bf0) (used)
      Origin IGP, metric 35060, localpref 150, invalid, internal
      Last update: Wed Aug 18 10:40:04 2021
rr# show ipv6 route 2c0f:fff0::/32
% Network not in table
2021/08/18 10:40:03 BGP: [Z2KFR-ZGJC8] 10.255.4.101 rcvd UPDATE w/ attr: , origin i, mp_nexthop 2001:978:2:6f::47:1(fe80::b696:91ff:fea6:9bf0), localpref 150, metric 35060, community <censor>, path <censor>
2021/08/18 10:40:03 BGP: [P9VY3-5B6NX] 10.255.4.101 rcvd UPDATE wlen 0 attrlen 93 alen 0
2021/08/18 10:40:03 BGP: [W0R38-AAD36] 10.255.4.101 rcvd 2c0f:fff0::/32 IPv6 unicast
2021/08/18 10:40:03 BGP: [J47J0-K06GG] Found existing bnc 2001:978:2:6f::47:1/128(VRF default) flags 0x2 ifindex 0 #paths 118558 peer 0x0
2021/08/18 10:40:03 BGP: [YT4EY-7V2YV] bgp_update(0.0.0.0): NH unresolved

@tobias-urdin
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The only way to workaround it is by using ipv6 nht resolve-via-default that will make it resolve the GA nexthop but use LL nexthop.

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5 participants