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Re: [Xen-users] How to tell which tapX interface belongs to which domain...

On October 9, 2007, Christian Horn wrote:
> - from the ping we have the mac in the arp-cache, and
> 'brctl showmacs xenadm0' shows the macs known on that bridge:
>    -----------
>    port no mac addr             is local?  ageing timer
>      2     00:03:d2:11:0d:fb    no            1.57
>    [....]
>      4     6e:14:9d:77:3a:cd    yes            0.00
>      4     aa:00:00:00:00:03    no          138.21
>      1     fe:ff:ff:ff:ff:ff    yes            0.00
>    -----------
> - the 'port' column of my well-known mac is important, its 4.
> Issuing 'brctl show' i get the connected tap-interface on the
> 4th line:
>    -----------
>    bridge name     bridge id       STP enabled     interfaces
>    xenadm0         8000.6e149d773acd       no      vif0.0
>                                                    peth0
>                                                    vif1.0
>                                                    tap0
>                                                    vif17.0
>    [.....]
>    -----------

One thing to watch out for: While the port number gets incremented for each 
device you add to the bridge, any devices that are removed leave a hole. If 
you remove vif1.0 from the bridge above, tap0 will still be port 4, but it 
will be the third entry in 'brctl show' output. If you start/stop instances a 
lot, you will run into that problem.

Unfortunately, the true mapping is not exposed to userspace. At least I could 
not find it in linux/if_bridge.h.

James Oakley

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