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Re: MTU of the Internet?

  • From: Eric Germann
  • Date: Wed Feb 04 15:45:59 1998 
-----Original Message-----
From: Robert E. Seastrom <[email protected]>
To: [email protected] <[email protected]>
Cc: [email protected] <[email protected]>
Date: Wednesday, February 04, 1998 1:40 PM
Subject: Re: MTU of the Internet?


<SNIP>

</SNIP>
>I have no idea where they came up with this "576 internally" nonsense.
>Generally whenever one runs into that number it is as a result of
>creaky old software that expects to be running over milnet or arpanet.
>

IPX used 576 forever whenever you had to cross IPX "subnets".  The reason
was simple.  They were lazy.  576 was the least common denominator between
Ethernet, TR, and _Arcnet_

Large IPX (LIPX) allowed them to do basically what IP calls Path MTU
discovery.  Only took them a day short of forever to figure out how to do
it.

>Are Microsoft stacks known to be broken in the packet
>fragmentation/reassembly department?  Or are just acknowledging
>deficiencies in their path mtu discovery code by setting the MSS in
>the basement?  I knew they had problems with window length (this from
>my friends with long fat pipes)...
>

With all the paranoids trying to block all ICMP, not just ICMP_ECHO, doesn't
that essentially break PMTUD.  576 may not be efficient, but its probably
the safest to assume.