[ovs-discuss] Flooding to multiple patch ports

Keith Holleman keith.holleman at gmail.com
Thu Oct 29 18:36:48 UTC 2015

I saw and followed the fairly recent discussion on the dev alias about
flooding and patch ports here:


But I have a slightly different question.  In one setup, I have two patch
ports connecting the same two bridges.  One bridge, is a "secure" bridge.
While not actually managed by a controller, it effectively is as all rules
are manually added in a very specific and controlled manner.  The other is
a standard stock "learning" bridge with only a normal action.  To borrow
and enhance the topology from the previous thread:

port_A --- br1 --- port_B (patch) ........ port_C (patch) --- br2 --- port_D

               --- port_E (patch) ........ port_F (patch) ---

The unexpected behavior that I'm seeing is that a broadcast packet
(say ARP) that arrives in br2 on patch port_C is not being flooded to
patch port_F.   That packet is however proper flooded to port_D and
any other ports (real or internal) in br2.  An ARP packet that arrives
on port_D is properly flooded to both port_C and port_F.  The rules in
BR1 do allow such a packet to arrive on port_A, leave on port_E, and
if it returns on port_B to to have a different set of rules applied
and may be resent out of port_A (or other ports in br1) after

Other things learned from experiments:

1) a unicast frame that arrives on port_C destined for a MAC learned
in br2 on port_F is properly forwarded out of port_F.  From this I
assume there is not a complete failure in sending from one patch port
to another between two bridges.

2) if I attach a new patch-port to br2 to another bridge (say br3),
the arp packet that arrives on patch port_C is flooded on the new
patch port to the new bridge.  From this I assume that you can flood
across patch ports just fine.

But there seems to be something or some check that is preventing a
broadcast packet arriving on port_C to be flooded out of port_F?   Is
there anything specific someone knows of that would prevent this or
any specific output or debug that could shed light on it?

Thanks for any help.
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