Date: Wed, 27 Jun 2001 21:12:32 +0400 From: Yar Tikhiy <yar@FreeBSD.ORG> To: Jonathan Lemon <jlemon@flugsvamp.com> Cc: audit@FreeBSD.ORG, net@FreeBSD.ORG Subject: Re: Long ether frames & MTU Message-ID: <20010627211231.B52886@comp.chem.msu.su> In-Reply-To: <20010625172318.C33375@prism.flugsvamp.com>; from jlemon@flugsvamp.com on Mon, Jun 25, 2001 at 05:23:18PM -0500 References: <20010625230255.A11496@comp.chem.msu.su> <20010625142542.Z33375@prism.flugsvamp.com> <20010626075624.D95583@gsmx07.alcatel.com.au> <20010625172318.C33375@prism.flugsvamp.com>
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On Mon, Jun 25, 2001 at 05:23:18PM -0500, Jonathan Lemon wrote: > On Tue, Jun 26, 2001 at 07:56:24AM +1000, Peter Jeremy wrote: > > On 2001-Jun-25 14:25:42 -0500, Jonathan Lemon <jlemon@flugsvamp.com> wrote: > > >On Mon, Jun 25, 2001 at 11:02:55PM +0400, Yar Tikhiy wrote: > > >> > > >> While more and more Ethernet NIC drivers start supporting long > > >> frames (>1518 bytes), the user/admin still cannot raise MTU on an > > >> Ethernet interface above the 1500 byte limit due to outdated code > > >> in net/if_ethersubr.c > > [patch removed] > > > > >I'm not at all sure how this change will help anything, unless each > > >driver alters if_hdrlen. > > > > One benefit is for 802.1Q VLAN support - the existence of lots of > > hard-wired values that restrict frames to 1518 bytes makes configuring > > VLAN's a pain. It would be nice if attaching a vlan(4) to a driver that > > handled 1522 byte frames resulted in a 1500 byte MTU on the vlan. > > Maybe I'm being dense here, but even with 1522 byte frames, the MTU > of the device should still be 1500. MTU in this context applies to IP, > so it wouldn't include either the vlan header or the ethernet header. You have a point there! I mistook the layer 3 (IP, IPX etc) MTU for the physical MTU of the ethernet NIC, which is rather high by default for many adapter types, unlike MRU. To run VLANs, one don't need to increase the IP MTU on the trunk interface. So I recall the patch, sorry. -- Yar To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-audit" in the body of the message
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