FreeBSD Bridge and ARP question/strangeness

Eygene Ryabinkin rea-fbsd at
Thu Nov 20 03:52:52 PST 2008

Cole, good day.

Thu, Nov 20, 2008 at 11:46:42AM +0200, Cole wrote:
> 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.

I think that the first thing to look at will be the tcpdump of the ARP
traffic -- if your peers are seeing '(incomplete)' as the bridging host
MAC, then it is good to check if ARP requests are received and are they
replied to.

'tcpdump -lvvnetti rl0 arp' should produce the fine listing.  And the
output of 'ifconfig' and 'sysctl' will be helpful too.
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 /  ' `         ,       __.--'      #  to read the on-line manual   
 )/' _/     \   `-_,   /            #  while single-stepping the kernel.
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