MTU to CDN's

Fri Jan 19 14:01:11 UTC 2018

Bah, never mind.. reading my PCAP wrong :-(

> On Jan 19, 2018, at 8:58 AM, Jared Mauch <jared at puck.nether.net> wrote:
> 
> 
> 
>> On Jan 18, 2018, at 8:44 PM, William Herrin <bill at herrin.us> wrote:
>> 
>>> Which packet?  Is there a specific CDN that does this?  I’d be curious to see
>>> data vs speculation.
>> 
>> Howdy,
>> 
>> Path MTU discovery (which sets the DF bit on TCP packets) is enabled
>> by default on -every- operating system that's shipped for decades now.
>> If you don't want it, you have to explicitly disable it. Disabling it
>> for any significant quantity of traffic is considered antisocial since
>> routers generally can't fragment in the hardware fast path.
> 
> I’m not seeing this in a PCAP capture to at least one CDN, either from my
> host or from the CDN endpoint.
> 
> I suspect you’re mistaken.
> 
> - Jared
> 
> PCAP: https://puck.nether.net/~jared/akamai.pcap