[Bug 263288] IPv6 system not responding to Neighbor Solicitation

From: <bugzilla-noreply_at_freebsd.org>
Date: Thu, 21 Apr 2022 13:59:01 UTC
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=263288

--- Comment #13 from wcarson.bugzilla@disillusion.net ---
I'm not sure how to answer your FIB questions, but here are the results of the
commands:

root@roast:~ # sysctl net.fibs
net.fibs: 1
root@roast:~ # sysctl net.add_addr_allfibs
net.add_addr_allfibs: 0
root@roast:~ # ifconfig em0 | grep fib
root@roast:~ #

Also as soon as I changed net.inet6.icmp6.nd6_onlink_ns_rfc4861 -> 1, it
started working. I find this very surprising because I hadn't even provisioned
this server yet in 2008, and IPv6 had worked for many years up until just
recently. Is the on-link flag a setting my provider could have changed?

Changing back net.inet6.icmp6.nd6_onlink_ns_rfc4861 -> 0 I expected it to break
so I could take a packet capture, and ... well, even after more than 15 minutes
it's still working. 

I did still have this in my scrollback, but I don't know if it has the data
you're looking for since it's not a full capture (tcpdump -nnvvv):

00:43:51.408006 IP6 (class 0xe0, hlim 255, next-header ICMPv6 (58) payload
length: 32) 2600:3c00::e6c7:22ff:fe10:9cc1 > ff02::1:ffb0:a56f: [icmp6 sum ok]
ICMP6, neighbor solicitation, length 32, who has 2600:3c00::f03c:91ff:feb0:a56f
          source link-address option (1), length 8 (1): e4:c7:22:10:9c:c1
            0x0000:  e4c7 2210 9cc1
00:43:51.408416 IP6 (class 0xe0, hlim 255, next-header ICMPv6 (58) payload
length: 32) 2600:3c00::e6c7:22ff:fe10:9cc1 > ff02::1:ffb0:a56f: [icmp6 sum ok]
ICMP6, neighbor solicitation, length 32, who has 2600:3c00::f03c:91ff:feb0:a56f
          source link-address option (1), length 8 (1): e4:c7:22:10:9c:c1
            0x0000:  e4c7 2210 9cc1

I will keep a close eye on this and try a reboot to see if it persists. If it
breaks again I will take a packet capture as described.

Thank you so much for all your help thus far!

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