[ntp:questions] multicast - TTL

David L. Mills mills at udel.edu
Thu Feb 22 06:10:32 UTC 2007


Martin,

Yes it does; see the RFC. In any case, you are free to design your own ttl.

Dave

Martin wrote:
>>The quick answer is to put this in your config file:
>>
>>ttl 0 1 2 3 4 5 6 7
>>
>>This creates a one-to-one mapping for ttl.
> 
> 
> There still seems to be a small problem ...
> 
> For multicast (224.0.1.1) it works as you have described, but
> for the regular UDP broadcast it does not.
> 
> The config file:
> 	ttl 0 1 2 3 4 5 6 7
> 	broadcast 192.168.XX.255 key 144 ttl 3
> 
> ntpd with -D2 flag says the TTL is 3:
> 	***** sendpkt(fd=20 dst=192.168.XX.255, src=192.168.XX.XXX, ttl=3, len=68)
> 
> but the tcpdump says the TTL is 64:
> 	IP (tos 0x0, ttl  64, id 0, offset 0, flags [DF],
> v
> The broadcast will not leave the LAN, so the TTL does not really matter,
> but the behaviour is strange.
> 
> 	Martin
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