Re: IPv6 path MTU discovery not working (large number of retransmited TCP data packets)

On Mon, May 26, 2025 at 09:15:17PM +0200, Jörg Sonnenberger wrote:
> On 5/26/25 6:41 PM, Christof Meerwald wrote:
> > The NetBSD VPS is using vioif0 with MTU 1500, but I am actually
> > connecting to the IPv6 address via an HE tunnel (so the MTU on the
> > path is lower).
> 
> Is your default route using the public address also used in the ICMP6 error
> or a link local address of the same suffix?

Not entirely sure what you are asking, but here are the contents of
the ICMP6 packet (as shown by ngrep -x):

 2001:470:0:221::2 -> 2a03:d9c2:100:49::b5d 2:0 #1
  00 00 05 b4 60 0c bf d7    05 b4 06 3c 2a 03 d9 c2    ....`......<*...
  01 00 00 49 00 00 00 00    00 00 0b 5d 20 01 04 70    ...I.......] ..p
  59 7a 0b bb 04 19 17 19    43 48 17 25 30 39 a8 da    Yz......CH.%09..
  e8 84 b8 cb a5 7e b3 1f    80 10 10 2c 67 29 00 00    .....~.....,g)..
  01 01 08 0a 00 00 00 01    49 65 cd b9 00 00 00 00    ........Ie......
  00 00 00 00 00 00 00 00    00 00 00 00 00 00 00 00    ................
...

It seems to match up (all public addresses).


Christof

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