[Linux-cluster] Multicast ccsd

Lazar Obradovic laza at yu.net
Thu Sep 2 13:58:01 UTC 2004

On Thu, 2004-09-02 at 00:53, Jonathan E Brassow wrote:
> Why did you choose 10?  I know that ttl == 1 is subnet... but 3-31 is 
> site local.  Is 10 a better choice than 3?  If so, why?  I can 
> certainly make something higher the default.

It depends on the site, mainly on network topology. Increment TTL for
every L3 device you have in the path between two cluster members. 
Value od 10 is something that "works for me" (c), since 10 is the
maximum path length my packets might have, even when flowing through
backup links. More standard setups (with servers into different vlans,
connected directly to L3 swtich) might use ttl = 3. 

One very important thing to do is to define access lists on
routers/switches, to allow only valid nodes to be senders and recievers.
Otherwise, someone else in the reach of mcast packets might listen to
cluster announcements, which might present security risk. 

> ttl could be a new option to ccsd - '-t <ttl>' for threshold or ttl.  
> Or, it could be part of the '-m' option, where the address and the ttl 
> would be separated by a ','.

It's better to leave it separate, that is, use "-t". 

> How does sound for a default?  This begs the question, 
> should I be using ff02::3:1 rather than ff02::1 for IPv6?

By looking at http://www.iana.org/assignments/multicast-addresses, you
can note that - is reserverd by IANA. 
On the other hand, seems to be unassigned.

I'm using for both ccsd and cman, so that might be a good
default :))

> On the other hand, have you tried compiling the modules outside the 
> kernel?  I'd be surprised if that didn't work yet...

This works more-or-less ok, but I have problem with
gfs-kernel/.../000001.patch, which *has* to be applied directly into
kernel, for it contains flock extensions. 

Nevermind, I'm patching by hand :)

Lazar Obradovic, System Engineer
laza at YU.net
YUnet International http://www.EUnet.yu
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