nxm_dst_check() requires a writable field. Since NX_LEARN_DST_MATCH only
matches on a field and doesn't write to a field, use nxm_src_check() for
that case instead.
Bug #7507.
Reported-by: Michael Mao <mmao@nicira.com>
There are a few loose ends here. First, learning actions cause too much
flow revalidation. Upcoming commits will fix that problem. The following
additional issues have not yet been addressed:
* Resource limits: nothing yet limits the maximum number of flows that
can be learned. It is possible to exhaust all system memory.
* Age reporting: there is no way to find out how soon a learned table
entry is due to be evicted.
To try this action out, here's a recipe for a very simple-minded MAC
learning switch. It uses a 10-second MAC expiration time to make it easier
to see what's going on:
ovs-vsctl del-controller br0
ovs-ofctl del-flows br0
ovs-ofctl add-flow br0 "table=0 actions=learn(table=1, hard_timeout=10, \
NXM_OF_VLAN_TCI[0..11], NXM_OF_ETH_DST[]=NXM_OF_ETH_SRC[], \
output:NXM_OF_IN_PORT[]), resubmit(,1)"
ovs-ofctl add-flow br0 "table=1 priority=0 actions=flood"
You can then dump the MAC learning table with:
ovs-ofctl dump-flows br0 table=1
