[Bug 263288] IPv6 system not responding to Neighbor Solicitation

From: <bugzilla-noreply_at_freebsd.org>
Date: Thu, 21 Apr 2022 09:15:06 UTC

--- Comment #11 from Zhenlei Huang <zlei.huang@gmail.com> ---
(In reply to wcarson.bugzilla from comment #10)

> However in the above debug message it added an extra :1 after ff02 in the 
> destination that does not appear in the tcpdump. Is that normal?
It may be the embedded form of IPv6 link-local scoped address, see
https://docs.freebsd.org/en/books/developers-handbook/ipv6/#ipv6-scope-index .

If your host is not for production, try turn on
'net.inet6.icmp6.nd6_onlink_ns_rfc4861' to see if it helps.

# sysctl net.inet6.icmp6.nd6_onlink_ns_rfc4861=1

Be aware that knob is to prevent CVE-2008-2476, see also

The symptom is weird, and I could not reproduce it.

Do you have multiple fibs? Check these:
# sysctl net.fibs
# sysctl net.add_addr_allfibs
# ifconfig em0 | grep fib

It will also be helpful if you provide traffic dumps.
# tcpdump -nvi em0 'icmp6' -w dump.pcap
and then 
# service rtsold restart && sleep 3 && ndp -c && ping6 ipv6.google.com

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