Date: Tue, 17 Jan 2012 01:28:23 +0100 From: Freek Dijkstra <public@macfreek.nl> To: freebsd-questions@freebsd.org Cc: Matt Mullins <mokomull@gmail.com> Subject: Re: Disable auto_linklocal Message-ID: <4F14C0A7.4060505@macfreek.nl> In-Reply-To: <CAPyT1SETL7%2BA3rgMWhwpFaD7HNCcp1FvT6ekzP2p0kpfOY2X6A@mail.gmail.com> References: <4F12F04B.2080504@macfreek.nl> <CAPyT1SETL7%2BA3rgMWhwpFaD7HNCcp1FvT6ekzP2p0kpfOY2X6A@mail.gmail.com>
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Matt Mullins wrote: >> The link-local addresses don't really harm, but I found them confusing, >> as the host is running as a router, and rtadv announces the link-local >> address by default. > > IPv6-standards-wise, this is the correct thing to do. Router > advertisements should contain link-local source addresses and > advertise the link-local address as the router; the globally-routable > prefix that is being advertised is a completely different field in > those messages. Hi Matt, Thanks for the info. I figured out as much. It is not possible to turn of link-local addresses in FreeBSD 9. Neither sysctl net.inet6.ip6.auto_linklocal=0 nor ifconfig em0 inet6 -auto_linklocal has any effect. The man page for ifconfig explicitly states that removing the link-local IPv6 address may result in unexpected behaviour The good news is that it *is* possible to use the global scope IPv6 address in router advertisements. RFC 4861, as you mentioned, defines a prefix. However, RFC 6275 alters the property of that field if a new flag, the router address flag, is set. In that case, the prefix field can contain the actual IPv6 address of the router. Apparently, this is needed for mobile IP. Unfortunately rtadvd (the default BSD router advertisement daemon) does not support this R-flag. The radvd daemon (available in a port) does support this bit by setting: AdvRouterAddr on Wireshark show that indeed this works. Unfortunately, most of my clients on the network still don't understand this bit, so it seems that after all I just have to remember the link-local IP addresses next to the global scope IP addresses for my network. Oh well, they say it's good to train one's memory :) Freek
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