[Bridge] IP address on bridged interface
simon at superduper.net
Thu Mar 5 08:53:25 PST 2009
Normally it does not make sense to put any L3 protocol address on port
interfaces - because incoming packets are diverted to the bridge
interface before the L3 protocol is examined. This means the L3 protocol
running on the port interface will never see any incoming packets.
There are a few rare circumstances where it makes sense to have IP
addresses on the port interfaces - it can be done with the use of the
ebtables BROUTE chain - this allows one to selectively pass frames to
the L3 protocol decode on a port rather than passing them to the bridge
interface. One situation where I have used this trick is on an NFS root
mounted networking device. On kernel boot the kernel NFS code assigns an
IP address directly to the ethernet port. Once my networking code starts
it creates a bridge and puts the ethernet port into the bridge. This
stops the NFS root mount from working, and the machine halts. The work
around is to put an ebtables rule in place to allow the NFS root mount
IP address to continue working.
Dirk Gouders wrote:
> I am currently playing with bridging to learn about various
> possibilities to setup a bridge to enable networking for KVM guests.
> I learned that I cannot use an IP address on one of the bridged
> interfaces but have to assign that IP address to the bridge interface if
> I want to use it to reach the bridge itself.
> The documentation I found does not say much about this subject and I am
> wondering whether there are situations when I can use IP addresses on
> bridged interfaces or if it absolutely makes no sense to have an IP
> address assigned to a bridged interface.
> Any explanation or pointers are very welcome.
> Bridge mailing list
> Bridge at lists.linux-foundation.org
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