[14982] in North American Network Operators' Group
Re: MTU of the Internet?
daemon@ATHENA.MIT.EDU (Eric Germann)
Wed Feb 4 15:26:46 1998
From: "Eric Germann" <ekgermann@cctec.com>
To: "Robert E. Seastrom" <rs@bifrost.seastrom.com>, <peterf@microsoft.com>
Cc: <nanog@merit.edu>
Date: Wed, 4 Feb 1998 15:06:25 -0500
-----Original Message-----
From: Robert E. Seastrom <rs@bifrost.seastrom.com>
To: peterf@microsoft.com <peterf@microsoft.com>
Cc: nanog@merit.edu <nanog@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.
