[Bridge] frame destinated to individual port MAC address

Benoit PAPILLAULT benoit.papillault at free.fr
Mon Aug 11 14:52:45 PDT 2008

Hash: SHA1

Hi there,

I'm working on very strange stuff using linux kernel bridge. Anyway, I
have a quick question.

Let's say I have 2 linux machines. Each has one bridge with several
interfaces. One interface of the first bridge (say eth0) is connected to
one interface of the other bridge (say eth0 again) using an Ethernet cable.

I have not configured an IP address on the bridge itself (on purpose)
but on each individual interface in the bridge. In order to be able to
communicate with those interfaces, I use ebtable broute rules in order
for the frame entering the bridge and with destination address being the
individual interface to be routed (-j DROP). Examples:

ebtables -t broute -L
Bridge table: broute

Bridge chain: BROUTING, entries: 4, policy: ACCEPT
- -d 0:ff:7f:dc:d3:4d -j DROP
- -d 0:ff:5e:7e:a5:ac -j DROP
- -d 0:ff:22:84:70:19 -j DROP
- -d 0:ff:2:fb:4:6d -j DROP

This is working as expected. So far, so good.

Now, using rtnetlink, I changed the port state (alternating between
learning and forwarding). In the learning state, ping is no longer
working between the 2 nodes. I would expect for the ping to be still
working (since IMHO bridge itself and its port should not be subject to
the bridge filtering rules).

Disclaimer : I'm not saying that the current linux implementation is
wrong, nor 802.1d is wrong.

Questions are :
- - according to 802.1d, what should happen to a frame with a destination
address being the MAC addr of a bridge port when it enters this bridge
port? Maybe this is outside of the scope of 802.1d since this frame is
not going to be "forwarded" in any way.

- - according to the current linux implementation, would it be a problem
to accept such frame? I tried a quick patch and it seems to be working.
However, it probably broke lots of other things.

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