MTU of the Internet?

Phil Howard phil at charon.milepost.com
Fri Feb 6 15:14:56 UTC 1998


Frank Kastenholz writes...

> note well that _none_ of this has to do with pmtu. none of this has
> to do with the oft-proclaimed poor quality of m.s. software.

Turn the MTU down, way down, and see how it affects things.  At what point
in number of connections does the problem happen with MTU=1500 and at what
point does it happen with MTU=600 and even MTU=200.

Of course changing MTU isn't the correct solution, nor is changing the
number of connections.  But these are workarounds that do work, for now.

Perhaps the retransmission timeout is the real problem as suggested, but
given there are different effects based on what client stack is used, as
apparently see on the end results and packet traces with Windows 95 and
Linux as the clients, there is some effect by the client.  That may not
be the true cause, but it should be discovered and logically ruled out if
it isn't.


> <soapbox>
> moral of the story
> theorizing is wonderful
> but a good packet trace beats a theory every time
> 
> and understanding how the protocols are _supposed_ to work
> and then trying to figure out why they don't is a lot more
> productive than bashing mammoth-software-corporations,
> though a lot harder
> </soapbox>

I'll admit to having never read the _whole_ protocol, so I will make a
point to do that at some point.  But having read the details on slow start
as a result of this thread, I find it's not what I proposed, although I
can now see that it, too, would have been explained as I explained my idea,
so the explanation was flawed.  I might try to implement my ideas via UDP
and see what kinds of effects I can really get over real networks of the
1990's, understanding that the original design was done in the 1980's and
before with slow links and slow routers.

-- 
Phil Howard | stop0it8 at anywhere.edu no3spam2 at s9p6a8m8.com stop2012 at anyplace.net
  phil      | ads6suck at lame8ads.net w2x7y5z2 at dumb6ads.com end8ads2 at anyplace.edu
    at      | blow1me4 at spam0mer.edu crash416 at no19ads1.com suck3it7 at no2place.edu
  milepost  | stop8149 at nowhere6.edu no88ads5 at no0where.org a5b7c4d9 at noplace5.net
    dot     | eat84me0 at dumbads2.com stop9ads at lame1ads.net die0spam at spammer9.com
  com       | end0ads2 at nowhere7.edu a9b4c4d7 at dumbads8.edu stop2ads at spammer9.org



More information about the NANOG mailing list