MTU to CDN's

Mark Andrews marka at
Sat Jan 20 06:01:18 UTC 2018

Which doesn’t work with IPv6 as UDP doesn’t have the field to clamp. 

Mark Andrews

> On 20 Jan 2018, at 03:35, Radu-Adrian Feurdean <nanog at> wrote:
>> On Fri, Jan 19, 2018, at 01:14, Jared Mauch wrote:
>> If you’re then doing DSL + PPPoE and your customers really see a MTU
>> of 1492 or less, then another device has to fragment 5x again.
> In this part of the world we have even worse stuff around: PPP over L2TP over over IP with 1500 MTU interconnection. Remove another 40 bytes. Add some more headers for various tunneling scenarios and you may get into a situation where even 1400 is too much.  But it usually works with MSS clamping to the correct value. Some small ISPs don't even make the effort to check if the transport supports "more than 1500" in order to give the 1500 bytes to the customer - they just clamp down MSS.

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