Re: [Int-area] draft-bonica-intarea-frag-fragile-01

[Mikael Abrahamsson <[e-mail]>]

On Thu, 31 May 2018, Joe Touch wrote:

> I disagree.
>
> UDP fragmentation has its benefits and uses, but should not be required when a transport layer isn’t needed - e.g., for IP tunneling.
>
> Fundamentally, IP fragmentation is fragile for only a few reasons:
> 1) the ID space is small (which shouldn’t matter unless there is a very large amount of reordering)
> 2) loss of fragments creates inefficiencies (true, but routers can fate-share fragments they drop sometimes, just as was eventually done for ATM AAL5)
> 3) in-network devices can’t find transport ports in some fragments, causing problems for NATs, policy filters and firewalls, etc.
>
> Of these, my view is that #3 is the only reason actually driving a claim of fragility - and all it tells me is that “the Internet is fragile when devices don’t follow the rules”.
>
> I do not think it is appropriate to validate that conclusion.

You're fundamentally right, unfortunately operational reality adds lots of 
more points to your list, meaning the end outcome is that IP fragmentation 
doesn't work well in real life.

I am as opposed to letting bad practices win as you probably are, but I 
also don't think this is fixable. This means applications need to have a 
mode where they do not rely on IP fragments for basic operation.

-- 
Mikael Abrahamsson    email: [e-mail]