MTU to CDN's

Jared Mauch jared at puck.nether.net
Fri Jan 19 00:41:37 UTC 2018


> On Jan 18, 2018, at 7:32 PM, William Herrin <bill at herrin.us> wrote:
> 
> On Thu, Jan 18, 2018 at 7:14 PM, Jared Mauch <jared at puck.nether.net> wrote:
>> lets say i can
>> send you a 9K packet.  If you receive that frame, and realize you need
>> to fragment, then it’s your routers job to slice 9000 into 5 x 1500.
> 
> In practice, no, because the packet you sent had the "don't fragment"
> bit set.

Which packet?  Is there a specific CDN that does this?  I’d be curious to see
data vs speculation.


> That means my router is not allowed to fragment the packet.
> Instead, I must send the originating host an ICMP destination
> unreachable packet stating that the largest packet I can send further
> is 1500 bytes.
> 
> You might receive my ICMP message. You might not. After all, I am not
> the host you were looking for.

:-)

Nor is it likely the reply.

- Jared


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