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[LaMont Jones <lamont.jones@xxxxxxxxxxxxx>]

Following apw's excellent advice pointing to
https://www.v13.gr/blog/?p=378 and abusing another ipv6 address on the
afflicted host:

tcpdump -npi br0 ip6 and not port 22 | grep -i neigh
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on br0, link-type EN10MB (Ethernet), capture size 262144 bytes

[ fire up ping6 2601:282:8100:3500:641d:9dd0:5b50:46e6 on the gateway.]
[ no traffic shows up on the bridge ]
[ echo 0 > /sys/devices/virtual/net/br0/bridge/multicast_snooping ]

09:40:49.260756 IP6 fe80::1 > ff02::1:ff50:46e6: ICMP6, neighbor solicitation, who has 2601:282:8100:3500:641d:9dd0:5b50:46e6, length 32
09:40:49.260813 IP6 2601:282:8100:3500:641d:9dd0:5b50:46e6 > fe80::1: ICMP6, neighbor advertisement, tgt is 2601:282:8100:3500:641d:9dd0:5b50:46e6, length 32

Looks like bridge multicast_snooping causes ipv6 neighbor discovery to
break.

-- 
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https://bugs.launchpad.net/bugs/1597806

Title:
  ipv6 neighbor discovery broken (on a bridge)

Status in linux package in Ubuntu:
  Confirmed

Bug description:
  I have a xenial (4.4.0-24-generic) machine that loses ipv6
  connectivity every time I reboot the gateway it uses.

  br0 is a bridge which has eth0.2 as its only member, with (currently) 6 "scope global temporary deprecated dynamic" (privacy) addresses, and:
      inet6 2601:282:8100:3500:24c:40ff:fe1a:c570/64 scope global mngtmpaddr dynamic
         valid_lft 300sec preferred_lft 120sec

  The tcpdump trace on against eth0.2 of the broken machine:
  http://paste.ubuntu.com/18170606/ (fe80::1 is the gateway)

  http://paste.ubuntu.com/18173670/ is the output of lspci -vvn on one
  of the (quad) interfaces on the machine.

  Setting the bridge to promisc and turning it back off works around the
  issue.  Tcpdump on the underlying eth0.2 does not.

  On another (yakkety) box, running 4-4-0.14-generic, I also see the
  problem: that interface is also br0, with eth0 (untagged) as its only
  member.

  All of the above leads me to believe that the kernel is not managing
  to correctly set up (at least some?) of the multicast addresses it
  needs to listen to on the bridge.

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