MTU of the Internet?

Wed Feb 4 20:06:25 UTC 1998

-----Original Message-----
From: Robert E. Seastrom <rs at bifrost.seastrom.com>
To: peterf at microsoft.com <peterf at microsoft.com>
Cc: nanog at merit.edu <nanog at merit.edu>
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.