Subject: Re: [Int-area] confirming consensus form themeeting: draft-templin-intarea-seal

From: [email-masked] (Noel Chiappa)
Date: Tue, 23 Feb 2010 20:44:04 -0500 (EST)

> From: "Templin, Fred L" <[email-masked]>

    > SEAL has now been published as an experimental RFC

I had a thought the other day, and this provides a good hook to ask about it.

My question is: as I expect you know, 'back in the day', in practise,
fragmentation turned out to just 'not work well'. I don't mean the code or
fragmentation/re-assembly algorithms didn't work, or anything - it's just
that in practise it provided poor performance.

This was touched on in a discussion on the Internet-History mailing list a
while back; you can find the most relevant message from the thread here:

  http://mailman.postel.org/pipermail/internet-history/2009-November/001084.html

So my question is: what expectation is there that router-to-router
fragmentation is going to work better than host-to-host fragmentation did
back then?

(This is not a snarky whack at SEAL, but a serious question. These MTU issues
are going to something _any_ encapsulation protocol is going to have to deal
with, and fragmentation is a mechanism any/all might use to help deal with
it. However, if router-to-router fragmentation doesn't work well, it's not
available for any of them.)

Now, I understand that the network is very different now from what it was
back then: congestion is much less of a problem, single-packet-buffered
interfaces are no longer common, etc, etc.

So perhaps it would work better now than it did 'back in the day', but at the
same time, I think you can see that a certain amount of reserve about this as
a potential solution is entirely reasonable?

Has there been any large-scale testing of router-to-router fragmentation,
across a variety of network paths, to see if the problems that plagued
host-to-host fragmentation are still with us?

	Noel

---

From: "Templin, Fred L" <[email-masked]>
Date: Wed, 24 Feb 2010 09:24:15 -0800

Hi Noel,

> -----Original Message-----
> From: Noel Chiappa [mailto:[email-masked]]
> Sent: Tuesday, February 23, 2010 5:44 PM
> To: [email-masked]
> Cc: [email-masked]
> Subject: Re: [Int-area] confirming consensus form themeeting: draft-templin-intarea-seal
> 

I understand that congestion is indeed much less
of a problem now.

> a potential solution is entirely reasonable?

Well, SEAL has been approx. 8 years in the making under
the public domain, so its not as if I'm popping up out
of nowhere to hit people over the head with it. Sure,
I expect skepticism, but I also expect discussion.

> host-to-host fragmentation are still with us?

I have been assured (nay, admonished!) by several from major
network equipment vendors that fragmentation is no longer a
performance concern as it once was; they did not say whether
the same was true about reassembly, however.

IP fragmentation was and still is considered harmful. That's
why SEAL does the most logical thing - it listens for IP
fragmentation and turns it off as soon as it hears any.

Thanks - Fred
[email-masked]