Date: Thu, 8 Jun 2000 09:22:33 -0400 (EDT) From: Jim Flowers <jflowers@ezo.net> To: "Kenneth D. Merry" <ken@kdm.org> Cc: Dave Preece <dave.preece@kbgroup.co.nz>, freebsd-hackers@FreeBSD.ORG Subject: Re: Path MTU discovery. Message-ID: <Pine.BSI.3.91.1000608091810.20995C-100000@lily.ezo.net> In-Reply-To: <20000608001317.A62030@panzer.kdm.org>
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And fbsd will respond to other's queries depending on interface mtus only be careful if you are running natd. This copies the interface mtu on startup but does not learn the new value if it is reduced either manually or automatically. It can therefore respond with a to a query with a value that is still unusable. Jim Flowers <jflowers@ezo.net> #4 ISP on C|NET, #1 in Ohio On Thu, 8 Jun 2000, Kenneth D. Merry wrote: > 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 > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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