FreeBSD Bridge and ARP question/strangeness

Ivan Voras ivoras at
Thu Nov 20 03:52:41 PST 2008

Cole wrote:
> Hi.
> I have been playing with FreeBSD bridging in 7.0-Release. And was just
> testing some things to see exactly how it worked and try a few things out. I
> know that this isn't how the bridge is meant to be setup, but now im just
> curious as to why the following is happening.
> I have a box with a few interfaces, and i had setup rl0 with an ip address
> and it could communicate/ping everything on the network fine, all the rest
> of the other interfaces are unplugged and have no ip's assigned. Now if i go
> ahead and create a bridge interface and then just add that single interface
> with the ip assigned to it to the bridge, without assigning a new ip to the
> bridge, i get some strange things happening. Every box on the network not
> running FreeBSD is still able to ping and receive a reply from the box on
> the ip it was using on the interface. However, no FreeBSD box is now able to
> ping the box at all. In the arp listing, it shows any of the FreeBSD boxes
> that are trying to ping it as "(incomplete)". But for every other box that
> isn't FreeBSD it gets a full arp listing and all those boxes are still able
> to communicate with the box fine.
> So i was just wondering if theres a reason for this, or if anyone has any
> idea or clues why this might be happening. If you want i can provide
> whatever dumps you would need or anything like that.

Can you rule out ARP timeouts? E.g. maybe other boxes have longer ARP
TTLs than FreeBSD boxes. It's happened to me once (it was a bug in the
em driver).

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