North American Network Operators Group

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Re: MTU of the Internet?

  • From: Alex P. Rudnev
  • Date: Wed Feb 04 15:29:59 1998

> > The reason for this change cited by many customers is that many ISPs have
> > 576 MTUs set "inside" their networks and packets get fragmented.
> I really don't buy that.  Many or most backbone links have MTU >1500, and
> MTUs <1500 outside of low-speed dialup connections aren't that common.
> They are there, yes.  But not that common.
> My understanding of why a lower MTU is demonstratable better under Win95
> is because the Win95 TCP stack is broken, and it is a good workaround.
Yep. And moreover; we mentioned the problem for the customers who use 
WIN95 and try to get information from some WIN-NT servers, in case if 
there is low-MTU (576) links somewhere between this client and server. I 
suppose Win95 TCP/IP stack is not implemented correctly for this issue.

> There are all sorts of people spouting all sorts of lies around Windows
> newsgroups about why small MTUs are good; I think novice users are simply
> getting drawn in by supposed experts.  
In theory, small MUS and priority queuering can make delays less; on 
practice (and if you remember about crasy and broken Win95 stack) the 
best choise is to use MTU 1500 everywhere when some Win95 customers exist.

Aleksei Roudnev, Network Operations Center, Relcom, Moscow
(+7 095) 194-19-95 (Network Operations Center Hot Line),(+7 095) 239-10-10, N 13729 (pager)
(+7 095) 196-72-12 (Support), (+7 095) 194-33-28 (Fax)