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Date: Thu, 7 Jun 2012 17:56:32 -0500 (CDT)
From: Robert Bonomi <bonomi@mail.r-bonomi.com>
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To: bruce@cran.org.uk, freebsd-questions@freebsd.org
In-Reply-To: <4FD12CFF.6020205@cran.org.uk>
Cc: 
Subject: Re: Configuration problem with IPv6 router ("cannot forward src")
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> From: Bruce Cran <bruce@cran.org.uk>
>
> I'm trying to set up a IPv6 router (running -current) on my home 
> network. My ISP gives me a /128 via PPP and I have a /48 allocation, 
> which I use to give em0 and tun0 public addresses in different subnets 
> (tun0 is assigned the address via ppp.linkup).
> I've added all the IPv6 settings to rc.conf (ipv6_gateway_enable, 
> ipv6_network_interfaces, rtadvd_enable etc.) and I can ping IPv6 sites 
> from the router.
>
> The problem is that rtadvd continues advertising the default gateway as 
> tun0's link-local address - and pinging from a machine on the network 
> results in "cannot forward src" messages on the router (strangely, 
> despite hisaddr being fe80::205:... in ppp.log, the kernel logs the 
> address as fe80:f::205:...).
>
> Is there some extra configuration I've likely missed that's needed when 
> using IPv6 via PPP?

Please provide the output from these two commands:
   ifconfig  -a
   netstat -nr
on both the router and on an 'inside' machine. (identifying which is which :)

There is also a question of 'where' the /48 comes from -- and how 
traffic to those addresses is being routed from the outside world.