bridge(4) and IPv6 link-local address

Chris Cowart ccowart at
Fri Apr 10 18:54:39 PDT 2009

Bjoern A. Zeeb wrote:
> On Mon, 30 Jun 2008, Eugene M. Kim wrote:
> > A quick question: Is bridge(4) supposed /not/ to automatically configure an 
> > IPv6 link-local address?
> yes there is a check for this in the code and if remoed (tried that
> lately) more things go wrong.
> > I'm trying to use it to bridge a wired segment and a wireless segment, and 
> > router advertisement over bridge0 wouldn't work because, with bridge0 lacking 
> > a LL address, the router uses a  non-LL address as the source address for RA 
> > packets, which then is ignored as invalid by other IPv6 nodes.
> yes, seem something similar lately but ETIMEOUT on debugging. The
> problem basically was:
>       lan    bridge    ath   ---  wlan client
> the LL address was on the "lan" interface.
> ping6 LL on lan from wlan client did not work. I could see the packets
> being bridged and visible on all interfaces and even the router on lan
> noticed them but there was no reply going to the client. ping6 from
> the bridge ``box'' to the wlan client and everything was fine as nd
> was seeded.
> Removing the check we ended up with the same LL address on both bridge
> and the lan interface if I can remember correctly and you do not want
> that... it's a bit tricky and there is something that does not work as
> expected, right. If you find the time to debug it I'll happily test
> patches;-)

I seem to be reviving a fairly old thread here, but this is what I found
when I went searching for the issue.

I am personally bridging a wireless NIC (ath0) with a VLAN interface
(vlan10). The bridge does not receive a link-local address. The bridge
interface (bridge0) is the default gateway for my LAN, both for v4 and

My Mac was logging this message in response to router advertisements:

| Apr 10 18:16:54 administrators-imac configd[29]: RTADV_VERIFY_PACKET:
| invalid RA with non link-local source from 2001:4830:1679:10::1 on en0

and was refusing to acknowledge them.

My solution was to assign a link-local address to bridge0 based on the
ethernet address (I think I did the EUI-48 stuff correctly):

| bridge0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
|     ether 92:db:a2:b4:8e:ba
|     inet netmask 0xffffff00 broadcast
|     inet6 2001:4830:1679:10::1 prefixlen 64 
|     inet6 fe80::90db:a2ff:feb4:83ba%bridge0 prefixlen 64 scopeid 0xc 
|     id 00:00:00:00:00:00 priority 32768 hellotime 2 fwddelay 15
|     maxage 20 holdcnt 6 proto rstp maxaddr 100 timeout 1200
|     root id 00:00:00:00:00:00 priority 32768 ifcost 0 port 0

According to ifconfig(8):

| Basic IPv6 node operation requires a link-local address on each interface
| configured for IPv6.  Normally, such an address is automatically config-
| ured by the kernel on each interface added to the system; this behaviour
| may be disabled by setting the sysctl MIB variable
| net.inet6.ip6.auto_linklocal to 0.

The bridge(4) page does not add any disclaimer about bridge interfaces.
Neither man page gives a good how-to on assigning your own link-local
address (I guessed and got it right with the % notation).

Shouldn't the kernel assign link-local addresses to these interfaces? Should
this address be based on the ethernet address of the bridge interface?
I'm not sure I really understood the challenges with the implementation.

Chris Cowart
Network Technical Lead
Network & Infrastructure Services, RSSP-IT
UC Berkeley
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 834 bytes
Desc: not available
Url :

More information about the freebsd-net mailing list