Finding MAC Addresses on bridge interfaces

Matthew Seaman m.seaman at
Sun Sep 5 04:47:35 PDT 2004

On Sun, Sep 05, 2004 at 10:54:45PM +1200, Mark Mumby wrote:
> Hi,
> I am running FreeBSD 4.9-RELEASE as a bridging ipfw firewall. What i
> would like to know is how to get the mac addresses of the upsteam and
> downstream neighbors (mac addresses of devices either side of the
> bridge) showing what interface they "appear" on.
> Using arp -a seems to associate the mac addresses with the interface
> that is configured with the management ip address 
> ie
>                 LAN A
>                     |
>          rl0
>                     |
>                  bridge
>                     |
>           xl0 un-numbered
>                     |
>                 LAN B
> When i do a arp -a, addresses on LAN B say they are on rl0 not xl0.

What does 'netstat -r' show you?  It should list all of the MAC
addresses in the routing cache, plus the interface it uses to
communicate to them.  You might need to ping various hosts judiciously
in order to get their details into the cache.



Dr Matthew J Seaman MA, D.Phil.                       26 The Paddocks
                                                      Savill Way
PGP:         Marlow
Tel: +44 1628 476614                                  Bucks., SL7 1TH UK
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