[Bug 272809] gre interfaces, tunnelfib is ignored

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=272809

            Bug ID: 272809
           Summary: gre interfaces, tunnelfib is ignored
           Product: Base System
           Version: 13.2-RELEASE
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: bugs@FreeBSD.org
          Reporter: dinoex@FreeBSD.org

I am unsing an IPv6 tunnel over gre

My setup works with FreeBSD-13.1

Host <-> Gateway <-> gre0 <-> Server

After Updating the gateway to FreeBSD-13.2
the routing over the tunnel failed.

Testing with tcpdump:
I see the response packages are visible on interface em0 instead on interface
vlan3.

It seems to me that "tunnelfib" is no longer evaluated.

To verify this I added an line to /etc/pf.conf:
pass in to 2XXX:XXXX:10::/64 rtable 3 no state

With this workaround in place the routing is working again.
Please look into this issue.

Diagnostics:

# ifconfig gre0
gre0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> metric 0 mtu 1476
        description: f2
        options=80000<LINKSTATE>
        tunnel inet X.X.X.15 --> X.X.X.2
        inet6 fe80::230:48ff:fecf:bcd0%gre0 prefixlen 64 scopeid 0x4
        groups: gre
        tunnelfib: 3
        nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>

# setfib 3 netstat -nr6
Routing tables (fib: 3)

Internet6:
Destination                       Gateway                       Flags     Netif
Expire
::/96                             ::1                           URS         lo0
default                           link#4                        US         gre0
::1                               link#3                        UHS         lo0
::ffff:0.0.0.0/96                 ::1                           URS         lo0
2XXX:XXXX:10::/64                 link#6                        U         vlan3
2XXX:XXXX:10::1                   link#6                        UHS         lo0
2XXX:XXXX:10::15                  link#6                        UHS         lo0
fe80::/10                         ::1                           URS         lo0
fe80::%vlan3/64                   link#6                        U         vlan3
fe80::230:48ff:fecf:bcd0%vlan3    link#6                        UHS         lo0
ff02::/16                         ::1                           URS         lo0

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