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From: vjs@rhyolite.wpd.sgi.com (Vernon Schryver)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: problem with ftp
Keywords: ftp tcp
Message-ID: <84890@sgi.sgi.com>
Date: 11 Feb 91 19:40:38 GMT
References: <1991Feb6.184300@sicsun.epfl.ch> <1991Feb9.190400.6078@Think.COM>
Sender: guest@sgi.sgi.com
Organization: Silicon Graphics, Inc., Mountain View, CA
Lines: 24

In article <1991Feb9.190400.6078@Think.COM>, barmar@think.com (Barry Margolin) writes:
>                                                            ....     Also,
> some TCP implementations use a larger MSS for subnet that are part of the
> same subnetted network than for outside networks (on the assumption that
> local area media are faster than wide area media, so the consequences of
> greater retransmission due to loss of a fragment are less severe).

Some might fear worse consequences of IP fragementation in such an
environment, because the routers are likely to be general purpose systems
which just happen to have additional ethernet interfaces, and may not have
an abundance of buffering.

The justification I've heard most often for such switches is that the MTU
in the local internet is at least as large as the MTU on local ethernet,
1500 bytes.  In such a case, 1500 causes no more fragmentation than 576.  I
have seen large commerical, production networks where using 1500 instead of
the approved 576 improved FTP performance 3X.


The default configuration on an IRIS is "allsubnetsarelocal=true".
Do you guys consider this Evil, Wrong, and Grounds for Belittling Remarks?


Vernon Schryver,   Silicon Graphics,  vjs@sgi.com