ICMPv6 "too-big" packets ignored (filtered ?) by Cloudflare farms

Fri Mar 8 17:40:42 UTC 2019

On Fri, Mar 8, 2019 at 5:45 AM Brandon Martin <lists.nanog at monmotha.net>
wrote:

> ICMP is nice in that it's totally protocol agnostic and doesn't require
> altering of packets in transit.  It's a shame we can't reasonably rely
> on it being delivered.
>

Path MTU discovery is broken. It's the one place in TCP/IP where the
end-to-end principle was thrown out the window and we keep on paying for it.

A correct solution would have been for the intermediate router to truncate
the packet. Not fragment, truncate. On receiving the truncated packet, the
RECIPIENT (not the intermediate router) would report the truncation to the
sender. This could easily have been done at layer 3, just like existing
PMTUD.

IPv4's inventors did a brilliant job with what they knew at the time.
IPv6's inventors not so much. Sadly, they were too busy figuring out how to
make IPv6 integrate well with ATM. Seriously, if you dig up a copy of the
original IPng book I think it's chapter 3.

Regards,
Bill Herrin

-- 
William Herrin ................ herrin at dirtside.com  bill at herrin.us
Dirtside Systems ......... Web: <http://www.dirtside.com/>
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