From owner-freebsd-hackers Wed Jun 7 23:13:34 2000 Delivered-To: freebsd-hackers@freebsd.org Received: from panzer.kdm.org (panzer.kdm.org [216.160.178.169]) by hub.freebsd.org (Postfix) with ESMTP id 9F31C37BA19 for ; Wed, 7 Jun 2000 23:13:25 -0700 (PDT) (envelope-from ken@panzer.kdm.org) Received: (from ken@localhost) by panzer.kdm.org (8.9.3/8.9.1) id AAA62116; Thu, 8 Jun 2000 00:13:17 -0600 (MDT) (envelope-from ken) Date: Thu, 8 Jun 2000 00:13:17 -0600 From: "Kenneth D. Merry" To: Dave Preece Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: Path MTU discovery. Message-ID: <20000608001317.A62030@panzer.kdm.org> References: <67B808B0DD93D211ABEE0000B498356B02BC70@internet.kbgroup.co.nz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2i In-Reply-To: <67B808B0DD93D211ABEE0000B498356B02BC70@internet.kbgroup.co.nz>; from dave.preece@kbgroup.co.nz on Thu, Jun 08, 2000 at 06:03:45PM +1200 Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG On Thu, Jun 08, 2000 at 18:03:45 +1200, Dave Preece wrote: > Just learning about this: I can see the advantages but does anything use it? Sure, TCP uses it. TCP (at least in FreeBSD) sets the "don't frag" bit on all its outgoing packets. If the packet gets to a router with an outgoing MTU that is too small to hold the packet without fragmentation, the router is supposed to send back and ICMP message telling the source machine to use a smaller packet size. When the source machine receives the ICMP message, it will update the MTU for that route, and try sending packets out again with the lower MTU. Ken -- Kenneth Merry ken@kdm.org To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message