North American Network Operators Group
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Re: MTU of the Internet?

  • From: Perry E. Metzger
  • Date: Wed Feb 04 12:39:52 1998 
Peter Ford writes:
> Several people have noted to the Microsoft Support and Product groups that
> they want the Windows 95 PPP MTU to be set to 576 (down from 1500).  this
> change is in Windows 98.
> 
> 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 know of no modern networking media in common use at ISPs that has an
MTU below 1000, and have not heard of ISPs with MTUs that low. Also,
the ISP's PPP could simply negotiate the MTU down -- it need not
accept a large MTU, no matter what Windows would like. The entire
story sounds, to say the least, fishy.

BTW, if Windows 95 is doing path MTU discovery, it should all be
irrelevant.

Perry