[ntp:questions] multicast - TTL

Martin martin at pr41.sk
Wed Feb 21 15:23:05 UTC 2007


> 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],

The broadcast will not leave the LAN, so the TTL does not really matter,
but the behaviour is strange.

	Martin



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