From owner-freebsd-questions  Mon Sep 22 07:29:37 1997
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To: Joe Beiter <jwb@xioa.cosmic.org>
cc: questions@FreeBSD.ORG
Subject: Re: SLIP and MTU 
In-reply-to: Your message of "Mon, 22 Sep 1997 09:23:06 EDT."
             <199709221323.JAA02814@xioa.cosmic.org> 
From: David Greenman <dg@root.com>
Reply-To: dg@root.com
Date: Mon, 22 Sep 1997 07:31:55 -0700
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>I began tracking a problem with sendmail getting "collect: I/O error blah blah"
>The sendmail FAQ cited MTU incompatibilities between myself and my ISP. My
>ISP told me my mtu should be set to 1536, which I set on my dip command line.
>
>However, when I do an "ifconfig sl0", it says my mtu is 552 and will not
>let me manually set it to 1536 from the command line claiming it is an
>illegal argument.
>
>Can anyone enlighten me on what is happening here?
>
>p.s. Don't bother telling me to use PPP. The version of code on the Bay
>routers my ISP is using does not like FreeBSD's PPP. Neither Bay nor the
>FreeBSD development group are concerned so that is why I'm stuck using slip.

   The maximum is 1500, so use that. That's a better value anyway since it's
also the ethernet MTU, which is often the limiting factor in the Internet.

-DG

David Greenman
Core-team/Principal Architect, The FreeBSD Project