[Linux-cluster] Choose between broadcast and multicast for cman

[Patrick Caulfield]

Riaan van Niekerk wrote:
> On Thu, 1 Jun 2006, Riaan van Niekerk wrote:
> 
>> Riaan van Niekerk wrote:
>>> Is there any reason or advantage to use multicast over broadcast, which
>>> offsets the complexity of multicast (relative to broadcast), e.g more
>>> control, less traffic, others?
>> Generally multicast behaves the same as broadcast. The only time you would
>> need multicast is if your nodes are on different subnets - in which case 
>> you
>> would also have to make sure the router had sufficiently low latencies to
>> support clustering over it.
>>
>>
> tnx Patrick
> 
> 
> The RHCS 4 documentation does not give a recommendation for a multicast
> address. cman man page and http://sources.redhat.com/cluster/doc/usage.txt
> mention 224.0.0.1, which is a non-routable multicast address range, 
> 224.0.0.0/24 .
> 
> So if I understand this correctly:
> 
> Using this address or anything in the 224.0.0.0/24 range would give the
> exact same effect as long as nodes are on the same subnet. If nodes are on
> different subnets, a multicast address in another network should be used
> (e.g. RHCS 3 defaults to 225.0.0.11).
> 

Exactly. I don't know just how that mcast address got into the documentation
but I suspect it's my fault. I do seem to remember giving someone a config
file with that address in it at some time :-)

-- 

patrick