Configuration problem with IPv6 router ("cannot forward src")

Matthew Seaman m.seaman at
Fri Jun 8 05:59:36 UTC 2012

On 07/06/2012 23:36, Bruce Cran wrote:
> 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.

rtadvd can be limited to operate on a specific interface.  Try setting


in /etc/rc.conf

> 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:...).

Try setting:


and possibly also

ipv6_defaultrouter="-interface tun0"

I use a gif tunnel (IPv6 over IPv4) for my IPv6 connectivity -- no
native support for IPv6 in my ADSL router -- so not exactly equivalent
but pretty similar in many ways.

> Is there some extra configuration I've likely missed that's needed when
> using IPv6 via PPP?

Probably.  The good news is that once you've got it running the IPv6
support in FreeBSD is rock solid and works like a charm.



Dr Matthew J Seaman MA, D.Phil.                   7 Priory Courtyard
                                                  Flat 3
PGP:     Ramsgate
JID: matthew at               Kent, CT11 9PW

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