[Int-area] Re: WGLC for "IP Tunnels in the Internet Architecture" draft-ietf-intarea-tunnels

[Ole Troan <[e-mail]>]

> Additionally:
> 
>> On Aug 7, 2025, at 1:15 PM, Templin (US), Fred L <Fred.L.Templin=[e-mail]> wrote:
>> 
>> Many tunneling protocols live by “grace” and assume 1500 everywhere. But, robust
>> tunneling protocols need to live by the “law”, and the law says 1280.
> 
> And its subtle - for IPv4, they assume 1500 everywhere but it’s really 576 after reassembly at the receiver.
> 
> For IPv6, it’s 1280 over each hop BUT up to 1500 after reassembly at each receiver.
> 
> These and other aspects are why this isn’t just an op-ed.

I think the current text is fine from a historical perspective.
For future recommendations I would prefer a recommendation that tunnels must support link-layer segmentation and reassembly.
That could be UDP options FRAG or something else.

Outer IP fragmentation is undesirable for multiple reasons.
E.g. a tunnel tail-end has to reassemble _before_ it can check if the fragment chain belongs to a tunnel. Last I looked, a lot of IP fragments are part of attacks, and they are costly to process.

Ole