[Linux-cluster] Howto multicast?

[Christine Caulfield]

Harri.Paivaniemi at tietoenator.com wrote:
> Please explain me,
> 
> I havn't use multicasting very much so now I have problems to understand this RHCS 5- communication.
> 
> I have tought it goes this way:
> 
> - cman uses either broadcast or multicast nowadays (multicast by default)
> - openais uses always multicast, with it's default address
> 
> Is this right? What is the difference there - if we have openais communicating, why there is another thing also communicating? I have been told that openais is cman's communication channel so what the heck?

There are several "other thing"s communicating, as well as openais. In
particular tou might see ccsd or DLM traffic. Neither of which uses the
openais transports.


> So, If I have 2 clusters in the same subnet, how to tell these things to be different?

cman separates the cluster by cluster name. In fact it hashes the name
into a 16 bit cluster number and uses that to generate a multicast
address. Though this can be overriden in cluster.conf. If you have two
cluster son one subnet then they will probably use different multicast
addresses if the hash is different. If you're unlucky enough to have a
clash of hashes and they two clusters decide to use the same multicast
address, then you can override either the cluster ID or the multicast
address.

<cman cluster_id="xxx" />

or
<cman> <multicast addr="239.192.204.100/>
</cman>

> 
> D. Teigland says:
> 
> ""
> When openais is started by cman, the openais.conf file is not used.  Many of
> the configuration parameters listed in openais.conf can be set in cluster.conf
> instead.
> 
> See the openais.conf man page for the specific parameters that can be set in
> these sections.  Note that settings in the <clusternodes> section will
> override any comparable settings in the openais sections above (in particular,
> bindnetaddr, mcastaddr, mcastport and nodeid will always be replaced by values
> in <clusternodes>).
> ""
> 
> So, if I put in cluster.conf:
> 
> <clusternode....>
> <multicast addr="239.192.204.100" interface="bond0"/>
> 
> ... for each node, what it configures? Cman or openais? 

cman runs as a plugin to openais. so cman uses openais as its messaggn
and membership system


-- 

Chrissie