[chrony-users] NTS dropped packets

[Kurt Roeckx <kurt@xxxxxxxxx>]

Hi,

I'm seeing dropped packets when talking to an NTS enabled server.
But I'm only seeing it on my home network, not on my server in the
datacenter. I currently see this using ptbnts1.ptb.de. I think I
had the same problem with nts.ntp.se, but it seems I changed from
an IPv4 address to an IPv6 address there and don't see the issue
since.

For ptbnts1.ptb.de I only get a reply every 4th packet. The packet
size gets larger when I don't get a reply, and then smaller again
when I do get a reply. The ntp packet sizes I see are:
232: no reply
340: no reply
448: no reply
556: reply
232: no reply

So the packet gets 108 bytes larger each time. The number of
extentions also increases. The extensions I see:
232: 0x0104, 0x0204, 0x0404
340: 0x0104, 0x0204, 0x0304, 0x0404
448: 0x0104, 0x0204, 0x0304, 0x0304, 0x0404
556: 0x0104, 0x0204, 0x0304, 0x0304, 0x0304, 0x0404

So 0x0304 (NTS Cookie placeholder) gets added in between. I guess
that's just because it used cookies and needs to get new ones.

A tcpdump on the remote site shows only the 556 byte packets
arriving.

Any idea what could be going on?


Kurt


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