MTU to CDN's

Thu Jan 18 23:50:42 UTC 2018

Because the CDN delivers to your customers not you.  It’s your customers link
requirements that are the ones you need to worry about.  If you support
jumbo frames to all of your customers and their gear also supports jumbo
frame then sure go ahead and use jumbo frames otherwise use the lowest
common denominator MTU when transmitting.  This is less than 1500 on
today Internet and encapsulated traffic is reasonable common.

	embedded CND <--> NAT64 <--> CLAT <--> client
		     1500       14XX     1500
	embedded CDN <--> B4 <— > 6RD <— > client
	             1500.   14XX     1500

Now you can increase the first 1500 easily.  The rest of the path not so
easily.

> On 19 Jan 2018, at 9:53 am, George Michaelson <ggm at algebras.org> wrote:
> 
> 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 telecurve.com> wrote:
>> Vincent,
>> 
>> Thanks. That URL explained a lot.
>> 
>> On Tue, Jan 9, 2018 at 3:11 AM, Vincent Bernat <bernat at luffy.cx> wrote:
>> 
>>> ❦  8 janvier 2018 15:08 -0800, joel jaeggli <joelja at bogus.com> :
>>> 
>>>>> 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:
>>> https://blog.cloudflare.com/path-mtu-discovery-in-practice/
>>> --
>>> Don't comment bad code - rewrite it.
>>>            - The Elements of Programming Style (Kernighan & Plauger)
>>> 

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