[ClusterLabs] corosync in multicast mode produces lots of unicast traffic

Jan Friesse jfriesse at redhat.com
Wed Oct 17 06:55:33 EDT 2018


> Hi Jan!
> Thanks for your answer.
>>> I have a Proxmox cluster which uses Corosync as cluster engine.
>>> Corosync uses the "default" multicast configuration. Nevertheless,
>>> using tcpdump I see much more packets sent by corosync using unicast
>>> between the node members than multicast packets.
>>> Is this normal behavior? If yes, please point me to some documentation.
>> It really depends. If cluster is quiet (no configuration changes) so it
>> basically only heartbeats then it's pretty normal that unicast trafic
>> (used for heartbeats) is bigger than multicast one.
> Now I am confused. I thought that corosync uses totem and the totem
> protocol has implicit keep-alive by passing the token between the ring
> members. So, even if there are no messages, the token is passed on in
> the ring giving implicit keep-alive. And all this is done using multicast.

Yes, it's exactly as you've wrote but these messages uses unicast. What 
I called heartbeat is exactly this token passing.

Multicast is used only for sending regular messages.

So if the cluster is quiet, only token passed between nodes using unicast.


> So, is my understanding wrong and corosync uses totem only for message
> delivery and there is an additonal "heartbeat" feature which sends
> unicast keep-alive to all the known members?
> Thanks
> Klaus

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