Date: Fri, 19 Jun 1998 23:16:45 -0500 (CDT) From: Joel Ray Holveck <joelh@gnu.org> To: spork@super-g.com Cc: opsys@mail.webspan.net, root@bmccane.maxbaud.net, hackers@FreeBSD.ORG Subject: Re: TweakDUN Message-ID: <199806200416.XAA11637@detlev.UUCP> In-Reply-To: <Pine.BSF.3.96.980619220851.25847A-100000@super-g.inch.com> (message from spork on Fri, 19 Jun 1998 22:17:09 -0400 (EDT)) References: <Pine.BSF.3.96.980619220851.25847A-100000@super-g.inch.com>
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>> Okay, I'm a bit confused here. How does the broken stack affect this >> issue? I thought it was a network design issue, since (if I >> understand correctly) many ISPs' uplinks use an MTU of 576, so any >> system using an MTU of 1500 (which includes the FreeBSD default) is >> going to have their packets broken into three packets of 576, 576, and >> 348 bytes. So, to reduce overhead, the MTU is set to 576 originally >> (why not 1152 I don't know) and life goes on. > I can't think of anywhere this is true. I'll use our dialup pools as an > example: > modem-> dialup PPP 1500 -> term server -> ethernet 1500 -> router -> T1(s) > HDLC 1500 -> core router -> fast ethernet 1500 -> upstream's border > router -> FDDI 40?? -> upstream core router -> ATM/SONET/whatever ? > Generally, one avoids small MTUs on big links, I beleive. ATM's small > cell size makes *every* packet get fragmented at layer 2, but I'm not sure > that's even relevant. > Anyone else? I've never heard of the oft quoted "Internet standard MTU of > 576"... Okay. I don't know much about ATM, etc, so I'll take your word for it. Happy hacking, joelh -- Joel Ray Holveck - joelh@gnu.org - http://www.wp.com/piquan Fourth law of programming: Anything that can go wrong wi sendmail: segmentation violation - core dumped To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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