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Old 02-08-2015, 01:36 AM   #1
psycroptic
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ntpd sending IPv6 packets with source link-local, destination global?


Noticed this in a packet dump recently on a Linux server on my LAN:

Code:
01:32:01.210795 IP6 fe80::20d:b9ff:fe33:198.123 > 2600:3c03::13:3123.123: UDP, length 48
01:32:01.211626 IP6 fe80::618:d6ff:fea1:dd3 > fe80::20d:b9ff:fe33:198: ICMP6, destination unreachable, beyond scope 2600:3c03::13:3123, source address fe80::20d:b9ff:fe33:198, length 104
It is ntpd attempting to contact the NTP server at 2600:3c03::13:3123, but using a source address of the interface's link-local. The router (at fe80::618:d6ff:fea1:dd3) then responds saying that it is (obviously) beyond the scope.

Why would this happen?
 
Old 02-08-2015, 05:58 PM   #2
Ser Olmy
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Does the system running ntpd have a public IPv6 address and a valid gateway entry in the routing table? If so, is ntpd actually bound to the "[Public_IPv6]/UDP/123" socket?
 
Old 02-08-2015, 07:39 PM   #3
psycroptic
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Quote:
Originally Posted by Ser Olmy View Post
is ntpd actually bound to the "[Public_IPv6]/UDP/123" socket?
This was the problem; it was listening on the link-local (since i never intended for it to accept incoming requests on a global address), but i didn't realize that doing this would also restrict its outgoing traffic. Changed "interface listen fe80::/64" to "interface listen ::/64" and all is well.

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