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

Fri Mar 8 13:45:20 UTC 2019

On 3/8/19 8:38 AM, Saku Ytti wrote:
> Hey,
> 
>>      now for UDP, I don't know yet how does things like QUIC can be handled ...
> 
> Unfortunately the magic answer you were hoping does not exist, what
> they do is they just send smaller packets.
> 

What we almost seem to be moving toward in this discussion is an IP 
header where the path can reduce the reported MTU which can then be read 
at the receiving end.  This would be somewhat like ECN just with more 
than a couple bits.

Of course, we know how well extension headers, much less hop-by-hop 
headers, are handled on IPv6...

Re-writing a field in the L4 header works, but it seems ugly since it 
means every hop that reduces the MTU of the link has to know every L4 
that participates in such a scheme.

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.
-- 
Brandon Martin