[Linux-cluster] TTL on multicast packets set to 1 by default?

[Steven Whitehouse]

Hi,

On Wed, 2007-09-19 at 01:25 -0700, Steven Dake wrote:
> My apologies I must have missed that email.
> 
> The code in openais is untested in a routed environment because I dont
> have any routed environments to test with.  This is why TTL is not
> configurable in the current openais or tested with any values greater
> then 1.  I can build you an RPM with ttl set to some greater value to
> test with if you like.
> 
> Regards
> -steve

The normal settings for multicast ttl are:
0 - node local
1 - link local
<32 - site local (so I guess a setting of 31 is reasonable here)
>128 - global

I also found a ref with the following extra values which I didn't
remember:
33-64 region local
65-128 continent local

I'm not sure if those last couple are official or not, 

Steve.


>  
> On Wed, 2007-09-19 at 18:15 +1000, Nikolas Lam wrote:
> > Some weeks ago I posted to this list reporting problems with my 2-node
> > RHEL5 cluster where I had each node on a different VLAN, connected by a
> > layer 3 router.
> > 
> > The problem was that the OpenAIS (cluster communications) packets were
> > not reaching the other node, so all sorts of annoying things were
> > happening.
> > 
> > Well, I've just had someone with extensive multicast experience help me
> > with some troubleshooting. We've discovered that the problem appears to
> > be that the packets are going out with a TTL of 1, which means the first
> > router to receive it will drop it without forwarding.
> > 
> > Here's a piece of tcpdump -v
> > 
> > 04:47:23.167506 IP (tos 0x0, ttl 1, id 0, offset 0, flags [DF], proto
> > UDP (17), length 102) 172.16.99.50.5149 > 239.224.72.11.5405: UDP,
> > length 74
> > 04:47:23.336194 IP (tos 0x0, ttl 1, id 0, offset 0, flags [DF], proto
> > UDP (17), length 102) 172.16.99.50.5149 > 239.224.72.11.5405: UDP,
> > length 74
> > 04:47:23.538871 IP (tos 0x0, ttl 1, id 0, offset 0, flags [DF], proto
> > UDP (17), length 146) 172.16.99.50.5149 > 239.224.72.11.5405: UDP,
> > length 118
> > 04:47:23.658161 IP (tos 0x0, ttl 1, id 0, offset 0, flags [DF], proto
> > UDP (17), length 102) 172.16.99.50.5149 > 239.224.72.11.5405: UDP,
> > length 74
> > 04:47:23.826268 IP (tos 0x0, ttl 1, id 0, offset 0, flags [DF], proto
> > UDP (17), length 102) 172.16.99.50.5149 > 239.224.72.11.5405: UDP,
> > length 74
> > 04:47:24.026863 IP (tos 0x0, ttl 1, id 0, offset 0, flags [DF], proto
> > UDP (17), length 146) 172.16.99.50.5149 > 239.224.72.11.5405: UDP,
> > length 118
> > 
> > 
> > So, I guess the question is, what is the correct method to set the TTL
> > to be a bit more reasonable, say 128?
> > 
> > Regards,
> > 
> > Nik Lam
> > 
> > --
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> > Linux-cluster at redhat.com
> > https://www.redhat.com/mailman/listinfo/linux-cluster
> 
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