Re: [Int-area] WG Adoption Call: IP Fragmentation Considered Fragile

[Joe Touch <[e-mail]>]

> On Aug 29, 2018, at 11:19 PM, Christian Huitema <[e-mail]> wrote:
> 
>> Regardless, middleboxes shouldn't be avoiding their own effort by creating work for others. A corollary to the Postal Principle should be "you make the mess, you clean it up". 
> 
> Joe's stubborn adherence to the letter of the RFC would be very nice if the protocol police could somehow punish the merchants of NATs…

My concerns are pragmatic - merely not supporting something does not make it unnecessary.

There was a time when Internet service in hotels would regularly block all except basically DNS and HTTP/HTTPS; that’s becoming much less the case. There was a time when devices didn’t support IPv6 at all because it was considered merely an unnecessary expense; that’s becoming much less the case too.

In this case, we have two problems 
	1) NATs/firewalls as currently implemented do not support fragments
	2) our current protocols, in many cases, require fragments (IPsec tunnel mode) and in other cases (tunnels in general) would benefit from IP fragmentation support
	3) we DO NOT HAVE an alternative (there are some piece-wise proposals for various aspects, but none support IPsec tunnel mode and none are otherwise universal

Yes, something needs to be done, but I argue that *until we have a worked alternative*, we need to keep restating the fact - NATs/firewalls MUST reassemble to work properly; where they don’t, the error is on them - not the rest of the Internet for using fragments.

> The whole discussion reminds me of Martin Thomson's draft, "use it or lose it" (draft-thomson-use-it-or-lose-it-02). Martin is describing how extension mechanisms that are not actually used get ossified away by the deployment of middle-boxes. The same happened long ago with IP segmentation. With NATs, applications cannot assume that reassembly will work. With Firewalls, transports cannot assume that ICMP will work. 

Yes, that’s the tension:
	a) identify bugs and fix them
	b) accept bugs as de-facto protocol evolution

The problem with (b) is that it is not guided by what Internet users need; it’s guided by what is profitable for individual vendors. That path is hazardous - there’s no reason to believe that the result will be a useful Internet. So until we know it’s safe to do (b), we need to stick with (a).

Joe