[ovs-discuss] Interval /transmission timer for particular MPs in CFM

Ethan Jackson ethan at nicira.com
Fri Feb 17 20:57:08 UTC 2012

  > Ed- same broadcast domain , you mean- I have to assign all MPs in one vlan
> or same network should be provided.

The CFM module sends multicast CCMs on the interface upon which it's
configured.  Presumably, multicast/broadcasts packets egressing this
interface can reach some set of other hosts on the network.  This set
can be restricted by using VLANs or other strategies.  How this is
done precisely, is out of the scope of the CFM module.  The important
thing is, when the CFM module broadcasts CCMs, all other MPs that
these CCMs reach need to have the same transmission interval.

>> > 2) along with that I want to know how can I see the current timer value
>> > by
>> > any show command for particular MPids, I didn' tfind any command for
>> > this.
>> ovs-appctl cfm/show will give you information about currently configured
>> CFM.

The CFM module doesn't maintain a separate timer for each remote MP.
Instead it maintains one timer that triggers at an interval of 3.5
times the transmission interval.  When the CFM module receives a CCM
from a remote MP, it sets a flag for this remote MP indicating the
reception.   When the timer triggers, any MPs which are not flagged
are considered unreachable and removed.  All of this information (the
timers, the set of reachable MPs, the reception flag) is available
from the ovs-appctl cfm/show command.

It's also worth noting that we don't implement the full 802.1ag
specification.  We implement a much simplified version which maintains
the packet format, but is quite a bit less sophisticated than the


> Ed- this command shows the configured CFM,my doubt was when CCM received
> then timer gets restarted then how can I check /verfiy this that timer has
> been restarted for a MP or MPs
>> Ethan
>> >
>> > Regards,
>> > Ed
>> >
>> > _______________________________________________
>> > discuss mailing list
>> > discuss at openvswitch.org
>> > http://openvswitch.org/mailman/listinfo/discuss
>> >

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