[Linux-cluster] multicast howto

[Patrick Caulfield]

Wolfgang Pauli wrote:
> Thanks!
> 
> First, I had to figure out how multicast works. Still don't fully understand 
> it. I can ping 224.0.0.1 and I get responses from all hosts in the same 
> subnet. It tried to ping 225.0.0.8 but that does not really work. But I don't 
> know whether it has to.
> I have changed the cluster.conf to have only two nodes. Just to get the basic 
> understanding. I have node dream on subnet 210 and neo on 223. They still 
> form their own clusters. Should I just try different addresses, or do the 
> switches/routers have to be programmed for that?


That cluster.conf file looks a lot more sensible. If the nodes are still not
seeing each other then you may have to fiddle with the routers to make sure
that the multicast traffic is being passed. tcpdump will tell you whether the
traffic is moving between subnets.

It's also worth checking that there aren't any iptables rules preventing
traffic from the cluster port (6809/udp) or the multicast address reaching the
cluster manager.

> regards,
> 
> wolfgang
> 
> <?xml version="1.0" ?>
> <cluster config_version="2" name="alpha_cluster">
>         <fence_daemon post_fail_delay="0" post_join_delay="3"/>
>         <clusternodes>
>                 <clusternode name="dream" votes="1">
>                         <multicast addr="225.0.0.9" interface="eth0"/>
>                         <fence>
>                                 <method name="1">
>                                         <device name="human" 
> nodename="dream"/>
>                                 </method>
>                         </fence>
>                 </clusternode>
>                 <clusternode name="neo" votes="1">
>                         <multicast addr="225.0.0.9" interface="eth0"/>
>                         <fence>
>                                 <method name="1">
>                                         <device name="human" nodename="neo"/>
>                                 </method>
>                         </fence>
>                 </clusternode>
>         </clusternodes>
>         <cman expected_votes="1" two_node="1">
>                 <multicast addr="225.0.0.9"/>
>         </cman>
>         <fencedevices>
>                 <fencedevice agent="fence_manual" name="human"/>
>         </fencedevices>
>         <rm>
>                 <failoverdomains/>
>                 <resources/>
>         </rm>
> </cluster>
> 
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-- 

patrick