From owner-freebsd-tokenring Fri Oct 13 10:53:49 2000 Delivered-To: freebsd-tokenring@freebsd.org Received: from heathers.stdio.com (heathers.stdio.com [199.89.192.5]) by hub.freebsd.org (Postfix) with ESMTP id 4DA6937B502 for ; Fri, 13 Oct 2000 10:53:47 -0700 (PDT) Received: from heathers (heathers [199.89.192.5]) by heathers.stdio.com (8.9.3/8.8.8) with ESMTP id NAA07713; Fri, 13 Oct 2000 13:53:44 -0400 (EDT) (envelope-from lile@stdio.com) Date: Fri, 13 Oct 2000 13:53:43 -0400 (EDT) From: Larry Lile To: Nicolai Petri Cc: freebsd-tokenring@FreeBSD.ORG Subject: Re: MTU size! In-Reply-To: <008301c0352d$2d471ed0$6732a8c0@atomic.dk> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-tokenring@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG On Fri, 13 Oct 2000, Nicolai Petri wrote: > Was is the correct MTU size for tokenring ?? > > Cisco says : > > Default Media MTU Values > Media Type Default MTU > Ethernet 1500 > Serial 1500 > Token Ring 4464 I have never found a hard and fast default value, so I punted and used 1500. It could have been worse, 576 seems to be very poplular due to bridging. I think that Cisco is probably following RFC 1042: Given a token-holding time of 9 milliseconds and a 4 megabit/second ring, the maximum packet size possible is 4508 octets including all octets between the access control and the FCS inclusive. This allows 4508 - 36 (MAC header+trailer with 18 octet RIF) - 8 (LLC+SNAP header) = 4464 for the IP datagram (including the IP header). However, some current implementations are known to limit packets to 2046 octets (allowing 2002 octets for IP). It is recommended that all implementations support IP packets of at least 2002 octets. > So should I change my MTU to 4464 on my TR interfaces ?? Give it a try and let us know how it works out. -- Larry Lile lile@stdio.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-tokenring" in the body of the message