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

[Mark Andrews <marka () isc org>]

> On 5 Mar 2019, at 5:18 pm, Mark Tinka <mark.tinka () seacom mu> wrote:
>
>
>
> On 5/Mar/19 00:25, Mark Andrews wrote:
>
> > Then Cloudflare should negotiate MSS’s that don’t generate PTB’s if
> > they have installed broken ECMP devices.  The simplest way to do that
> > is to set the interface MTUs to 1280 on all the servers.  Why should
> > the rest of the world have to put up with their inability to purchase
> > devices that work with RFC compliant data streams.
>
> I've had this issue with cdnjs.cloudflare.com for the longest time at my
> house. But as some of you may recall, my little unwanted TCP MSS hack
> for IPv6 last weekend fixed that issue for me.
>
> Not ideal, and I so wish IPv6 would work as designed, but…

It does work as designed except when crap middleware is added.  ECMP
should be using the flow label with IPv6.  It has the advantage that
it works for non-0-offset fragments as well as 0-offset fragments and
also works for transports other than TCP and UDP.  This isn’t a protocol
failure.  It is shitty implementations.

> Mark.

-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742              INTERNET: marka () isc org