[Bug 263288] IPv6 system not responding to Neighbor Solicitation

From: <bugzilla-noreply_at_freebsd.org>
Date: Fri, 02 Aug 2024 18:14:48 UTC
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=263288

Florent Delahaye <bugfreebsd@undead.fr> changed:

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                 CC|                            |bugfreebsd@undead.fr

--- Comment #22 from Florent Delahaye <bugfreebsd@undead.fr> ---
Hello,

I have got the same issue with the same symptoms as OP and using
net.inet6.icmp6.nd6_onlink_ns_rfc4861=1 trick solved it too.

I have got a router aka router1 announcing a prefix that freebsd (and other
hosts) uses with SLAAC. There is another router aka router2 using another
prefix only announcing a route to itself (its prefix is not announced since no
SLAAC or DHCP is expected on that prefix). All devices (routers + host) are
using the same segment.
Freebsd host gets all RA and route table is properly populated. If I try a ping
from freebsd host to router2 then router2 sends back a NS and freebsd host
never replies.

I have not checked the code but
https://www.freebsd.org/security/advisories/FreeBSD-SA-08:10.nd6.asc says "The
solution described below causes IPv6 Neighbor Discovery Neighbor Solicitation
messages from non-neighbors to be ignored"
-> It seems the patch misinterprets the definition of a neighbor since all
hosts sharing a segment are neighbors.

FYI no issues with Linux/Windows/Android stacks.

Florent

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