[Bug 249253] missing nd6 Neighbor Advertisement on carp failover

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=249253

            Bug ID: 249253
           Summary: missing nd6 Neighbor Advertisement on carp failover
           Product: Base System
           Version: 12.1-RELEASE
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: kern
          Assignee: bugs at FreeBSD.org
          Reporter: claus.riegg at makandra.de

We're experiencing delay on CARP failovers with IPv6 in multiple setups at the
moment. 

Transition from BACKUP to master works fine and Gratuitous ARP is sent for all
IPv4 addresses immediately. The unsolicited Neighbor Advertisement for IPv6
seems to be missing (at least we don't see it when capturing traffic with
TCP-dump). 

Future Neighbor Solicitations will be answered by the current CARP MASTER
correctly but until then traffic is still arriving at the BACKUP (former
MASTER). 

Google returned this blogpost:
https://www.stoklasa.one/carp-with-ipv6-protocol/
Josef Stoklasa seems to think that this is normal behaviour but looking at
carp_master_down_locked function here looks like that there should be an
unsolicited Neighbor Advertisement:

https://github.com/freebsd/freebsd/blob/03c216ce761c84dbe6ab7611453931211e923986/sys/netinet/ip_carp.c#L1280

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