Subject: Re: picking an MRRU for MP

From: [email-masked]
Date: Fri, 26 May 2000 17:36:16 -0400

James,

> As long as you do the negotiation correctly and you allow the user
> to configure desired values, it's hard to see how you can go too
> terribly wrong here.

What I failed to state clearly in my previous note is that currently I was
NOT going to allow the user to configure the MRRU value directly. I'd
prefer not to throw "yet another" configuration choice at our customers
unless I see a compelling reason the customer needs to choose. And so far,
I just don't see this.

I would prefer that the code choose a "good" value for the MRRU. Probably
based on the configured MRU values for the links that could be bundled
together so that the customer's settings for the MRU gets reflected into
the MRRU.

Currently the code sets the MRRU equal to the MRU of the first link in the
bundle "plus a few 10's of bytes". The feeling I'm getting is that choice
is probably consistent with the typical settings of other PPP-MP
implementations. Yes? No? Maybe?

-john martz, 8-852-5539,  [email-masked]
IBM AS/400 TCP/IP PPP development (and stuff)

---

From: James Carlson <[email-masked]>
Date: Thu, 26 May 1994 19:40:35 -0400 (EDT)

> unless I see a compelling reason the customer needs to choose. And so far,

If all that you're supporting is low-speed (async and sync dial-up)
links, I guess that wouldn't cause too much trouble.

I agree that the customer shouldn't *have* to choose.  That's what
default values are for.  As a general matter, I absolutely hate
software that thinks it knows better than I about what I need to do in
all cases.  Hide the option in a "for experts only" menu if you must,
but omitting configuration variables entirely in the name of
ease-of-use is (in my opinion) simply wrong.  AIX is after all Unix,
not Windows.  ;-} (And, for what it's worth, AIX is the OS I'm using
at home ...)

In other words, the metric shouldn't be a compelling reason to choose
-- it should be a compelling reason to be *unable* to choose.

> together so that the customer's settings for the MRU gets reflected into

?  There's no particularly good relationship between MRU and MRRU that
I think you can use here.  MRRU on MP links is basically the IP MTU.
The MRU is hidden by MP and constitutes the maximum fragment size.

> implementations. Yes? No? Maybe?

Possibly so.  That's certainly not true in any of the implementations
I've worked on, but I can see how such a thing could happen ...

-- 
James Carlson                                  <[email-masked]>
"PPP Design and Debugging" --- http://people.ne.mediaone.net/carlson/ppp