Re: Bridge stays down until a port is added

On Sat, 20 Aug 2011 11:47:12 +0200
Marc Haber [off-list ref] wrote:

Hi,

I was a little bit confused. The problem is that with IPv6 an IP
address configured on a bridge which is still in the NO-CARRIER state
will never leave tentative state and will thus not get useable.

On Fri, Aug 12, 2011 at 02:22:27PM +0200, Sven-Haegar Koch wrote:

quoted

For me (using kernel 3.0.0) it seems to work as I expect it:

aurora:~# brctl addbr br0
aurora:~# ifconfig br0 192.168.254.1 netmask 255.255.255.0 up
aurora:~# ping 192.168.254.1
PING 192.168.254.1 (192.168.254.1) 56(84) bytes of data.
64 bytes from 192.168.254.1: icmp_req=1 ttl=64 time=0.087 ms

Now try it with IPv6.

The problem is that IPv6 Duplicate Address Detection needs to
work. This is not a simple problem.  If the bridge asserted
carrier with no ports then:

1. IPv6 address assigned and IPv6 decides it is okay.
2. Port added later
3. Another system has the same address.
*broke*

If you want to avoid DAD, then you can configure disable DAD
by setting /proc/sys/net/ipv6/conf/br0/accept_dad to 0