MSGID: <10jigka$3k8b9$1@dont-email.me> 68b11707
REPLY:  a883e8d7
PID: PyGate 1.5.2
TID: PyGate/Linux 1.5.2
CHRS: ASCII 1
TZUTC: 0000
REPLYADDR Pancho.Jones@protonmail.com
REPLYTO 3:633/10 UUCP
On 1/4/26 15:20, Richard Kettlewell wrote:
> Pancho  writes:
>> Richard Kettlewell wrote:
>>> https://www.greenend.org.uk/rjk/tech/nat.html has a worked example.
>>
>> Curiously  is an
>> example of a website that fails to load when I use IPv6 but works fine
>> under IPv4
>>
>> curl -4 https://www.greenend.org.uk/rjk/tech/nat.html
>> works fine
>> .
>> curl -6 https://www.greenend.org.uk/rjk/tech/nat.html
>> times out.
> 
> It works for me from a couple of locations (one with native IPv6 and
> the other via a Hurricance Electric tunnel). traceroute -6 might reveal
> where your problem is.
> 
>> Last thing I receive in IPv6 pcap from Greenend says
>> [TCP Previous segment not captured]
> 
> AFAICT that just means you started tracing part way through a session.
> 

Thanks both of you, that gave me confidence to investigate further.

I'm guessing it is due to  a split TCP packet. TLS asks for a change of 
cipher, which is a big packet, and then it all goes wrong.

Anyway, setting MTU=1444 fixes the problem. Internet tells me that the 
root problem is because the firewall is blocking ICMP too big, breaking 
Path MTU Discovery (PMTUD) . I can't see where, so now I have to 
understand that.

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