MTU/MSS testing IPv6

[Brian E Carpenter]

On 26/05/2016 00:33, Ignatios Souvatzis wrote:
> On Fri, Apr 29, 2016 at 08:30:50AM +0200, Mikael Abrahamsson wrote:
>>
>> Hi,
>>
>> I've run into a scenario where a website doesn't seem to be listening to
>> PTB. I can reach them just fine from an MTU1500 clean IPv6 connection, but
>> if I reach from a MTU1500<->MTU1480<->MTU1500 connection, it doesn't work. I
>> don't get the big packets after SYN handshake.
>>
>> I've been considering asking iis.se (the .SE ccTLD registry) who are already
>> running multiple testing tools for web sites and domain name owners) to
>> include these kinds of testing, and perhaps develop more of them.
> 
> Yes please.  Guess what I'm trying to debug right know, and having a 
> reliable testing point out there would be an immense help.

Make sure you cover MSS negotiation failure as well as PMTUD failure.
I've seen that cause things to stop after the SYN even if the MTU was
reduced correctly.

    Brian