Date: Thu, 16 Jun 2011 16:42:14 +0900 (JST) From: Hiroki Sato <hrs@FreeBSD.org> To: spork@bway.net Cc: freebsd-net@FreeBSD.org Subject: Re: link-local needed w/static IP and gateway? Message-ID: <20110616.164214.301126302041762988.hrs@allbsd.org> In-Reply-To: <4DF9ACCC.5070506@bway.net> References: <4DF9970D.5000505@bway.net> <20110616.145712.10896502890982069.hrs@allbsd.org> <4DF9ACCC.5070506@bway.net>
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Charles Sprickman <spork@bway.net> wrote
in <4DF9ACCC.5070506@bway.net>:
sp> > LLA is a MUST for every IPv6-speaking interface, not for automatic
sp> > router discovery only. This is because ICMPv6 heavily depends on it.
sp> > Without LLA some unexpected and/or inconsistent behaviors can happen,
sp> > especially on a router as you experienced.
sp>
sp> I'm puzzled by why hosts with static IPv6 IPs could communicate with
sp> each other. I noticed in some of my netstat output that even though the
sp> ff02 multicast network was in the table, it was only bound to the
sp> loopback. However I still logged multicast to/from the box. One of the
sp> RFCs also noted that multicast is limited in scope to the link-local
sp> address, so in theory, not even the host to host ND should have worked.
sp> I guess that's what threw me.
This is because an L3 address to an L2 address resolution in NDP
works in the host-to-host case by chance; addresses in the NDP
messages do not have to have a link-local scope and FreeBSD's
implementation uses a GUA if it is configured. The host-to-router
case doesn't work properly because a router with no LLA never accepts
multicast listener discovery messages.
You can observe tcpdump output of the host-to-host case and the
host-to-router case. The primary difference will be that the
unspecified address ("::") is used in MLD report messages in the
latter.
-- Hiroki
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