This is an issue I discovered while testing fixes for OVSDB-206.

In my test, I disabled the interface in the external router, so ODL
would send the ARP queries okay, but no responses from router even
make it back. In this situation, the temporary flow added in br-ex
that makes the potential arp response go back to the controller is
never removed.

This is also an issue when the periodic responder is removed or
it is not configured to probe for mac periodically.

===

[vagrant@devstack-control devstack(keystone_user1)]$ sudo ovs-ofctl O OpenFlow13 dump-flows br-ex | cut -d',' -f3
OFPST_FLOW reply (OF1.3) (xid=0x2):
table=0, n_packets=124, n_bytes=6440, priority=0 actions=NORMAL
table=0, n_packets=39, n_bytes=1638, priority=10000,arp,dl_dst=fa:16:3e:d7:4e:e7,arp_spa=192.168.111.254,arp_tpa=192.168.111.21,arp_op=2,arp_tha=fa:16:3e:d7:4e:e7 actions=CONTROLLER:65535
table=0, n_packets=479, n_bytes=52211, dl_type=0x88cc actions=CONTROLLER:65535
[vagrant@devstack-control devstack(keystone_user1)]$

vagrant@devstack-compute-1:~/devstack$ sudo ovs-ofctl O OpenFlow13 dump-flows br-ex | cut -d',' -f3
OFPST_FLOW reply (OF1.3) (xid=0x2):
table=0, n_packets=106, n_bytes=5684, priority=0 actions=NORMAL
table=0, n_packets=40, n_bytes=1680, priority=10000,arp,dl_dst=fa:16:3e:d7:4e:e7,arp_spa=192.168.111.254,arp_tpa=192.168.111.21,arp_op=2,arp_tha=fa:16:3e:d7:4e:e7 actions=CONTROLLER:65535
table=0, n_packets=520, n_bytes=56680, dl_type=0x88cc actions=CONTROLLER:65535
vagrant@devstack-compute-1:~/devstack$

vagrant@devstack-compute-2:~/devstack$ sudo ovs-ofctl O OpenFlow13 dump-flows br-ex | cut -d',' -f3
OFPST_FLOW reply (OF1.3) (xid=0x2):
table=0, n_packets=82, n_bytes=4676, priority=0 actions=NORMAL
table=0, n_packets=523, n_bytes=57007, dl_type=0x88cc actions=CONTROLLER:65535
vagrant@devstack-compute-2:~/devstack$