MTU to CDN's

George Michaelson ggm at
Thu Jan 18 22:53:36 UTC 2018

if I was an ISP (Im not) and a CDN came and said "we want to be inside
you" (ewww) why wouldn't I say "sure: lets jumbo"

not even "asking for a friend" I genuinely don't understand why a CDN
who colocates and is not using public exchange, but is inside your
transit boundary (which I am told is actually a bit thing now) would
not drive to the packet size which works in your switching gear.

I understand that CDN/DC praxis now drives to cheap dumb switches, but
even dumb switches like bigger packets dont they? less forwarding
decision cost, for more throughput?

On Fri, Jan 19, 2018 at 6:21 AM, Dovid Bender <dovid at> wrote:
> Vincent,
> Thanks. That URL explained a lot.
> On Tue, Jan 9, 2018 at 3:11 AM, Vincent Bernat <bernat at> wrote:
>>  ❦  8 janvier 2018 15:08 -0800, joel jaeggli <joelja at> :
>> >> N00b here trying to understand why certain CDN's such as Cloudfare have
>> >> issues where my MTU is low. For instance if I am using pptp and the MTU
>> is
>> >> at 1300 it wont work. If I increase to 1478 it may or may not work.
>> > PMTUD has a lot of trouble working reliability when the destination of
>> > the PTB  is a stateless load-balancer.
>> More explanations are available here:
>> --
>> Don't comment bad code - rewrite it.
>>             - The Elements of Programming Style (Kernighan & Plauger)

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