OTV route dampening

[zerorange]

Greetings, everyone.

I have a problem with OTV on N77k platform.

Some MAC addresses that are advertised via overlay interface are dampened in receiving side.

This is how it looks like:

acme-core-otv# show otv route



OTV Unicast MAC Routing Table For Overlay1



VLAN MAC-Address     Metric  Uptime    Owner      Next-hop(s)

---- --------------  ------  --------  ---------  -----------

956 0009.6b7f.47da  42      2d01h     overlay    foo-core-otv

956 0019.9c03.2060  42      00:45:51  overlay    foo-core-otv  (D)

956 0019.9c04.524e  1       00:05:15  site       port-channel94

956 0019.9c04.85ab  42      00:12:49  overlay    foo-core-otv

975 b8ac.6f3a.4679  42      23:18:30  overlay    foo-core-otv  (D)

975 b8ac.6f3a.8754  42      23:18:30  overlay    foo-core-otv



D - Being dampened

As a result, these MAC addresses are not advertised any further on the receiving side.

It seems to me there is no correlation between dampened MAC addresses.

I haven't found anything relevant in OTV docs, though I assume dampening is a feature of ISIS protocol.

Could anyone advise where I should start digging? In what cases dampening is used in ISIS?

[Steve Fuller]

Hi,

This is only from theory as I’ve not seen this myself, but from what I’ve read one of the reasons you see dampened entries in show otv route is if the remote AED changes.

Are you seeing any OTV adjacency changes or any changes affecting the AED in the remote site e.g., AED internal interface state changes, that might cause it to send an update to the OTV device you captured the above from?

Regards

[zerorange]

Hi Steve,

Thanks for the suggestion, but we haven't implemented second OTV devices yet. We have only one device on each site.

[Steve Fuller]

What does the remote AED i.e., foo-core-otv show for a MAC address that's dampened?

For example, if you go to remote OTV router and run the command show mac addr addr 0019.9c03.2060 do you see a local entry in the CAM? Presumably you see it as a locally learned MAC address and the aging timer is being reset i.e., it's not a "silent host".

Regards

[zerorange]

It appears we've solved the problem.

The reason was in L2 loop (via overlay) between two sites. The same MAC address has been systematically learned on overlay interface and on internal interface.

We've removed the loop, and amount of dampened routes decreased.

There are still few dampened routes in OTV routing table, but they appear exactly in 30 minutes after the route has been learned.

I suppose after MAC address is flushed from local OTV device FDB (due to aging), it is marked as Dampened on another side of overlay.

In that case I'm not sure if Dampened route is actually used for forwarding or not. Is there any information on that subject?