Date: Sun, 21 Feb 1999 11:16:34 -0600 From: Guy Helmer <ghelmer@scl.ameslab.gov> To: David Greenman <dg@root.com> Cc: Luigi Rizzo <luigi@labinfo.iet.unipi.it>, wpaul@skynet.ctr.columbia.edu, hackers@FreeBSD.ORG Subject: Re: How to handle jumbo etherney frames Message-ID: <Pine.SGI.4.05.9902211103430.9889-100000@demios.scl.ameslab.gov> In-Reply-To: <199902211235.EAA12927@implode.root.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On Sun, 21 Feb 1999, David Greenman wrote: > >> The jumbo frames are only useful if you also have VLAN support, which we > >> don't have currently. We also need support for large mbuf clusters; this > > > >hmmm i don't get this -- why is this related to VLAN ? > > Because most ethernets consist of a mix of hosts that don't have jumbo > frame capability. If you use jumbo frames without VLANs, then ALL hosts must > support jumbo frames (and I think would also have to be gigabit ethernet > connected since jumbo frames weren't supported in 802.3...although I'm > assuming that the gigabit spec allows for jumbo frames, which may be a > bad assumption on my part). AFAIK, Alteon is the only source right now for a Gigabit Ethernet switch that can handle jumbo frames (we have one on-site right now), and it will automatically fragment packets when a jumbo frame is forwarded to a link that uses normal frames. Seems like VLANs will not be necessary, as long as other switch manufactures provide this feature. (I'm not sure what the performance hit due to fragmentation would be, though.) BTW, we've found that jumbo frames make a significant difference in performance on the new RS/6000's we have -- peak TCP performance jumps from the 500Mbps range to the 800Mpbs range for 1500 vs. 9000 byte MTU. We assume that the Gigabit NICs in the RS/6000's are Alteon NICs, but there is no identification on the NICs other than IBM's. Guy Helmer, Ph.D. Candidate, Iowa State University Dept. of Computer Science Research Assistant, Ames Laboratory --- ghelmer@scl.ameslab.gov Research Assistant, Dept. of Computer Science --- ghelmer@cs.iastate.edu http://www.cs.iastate.edu/~ghelmer To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?Pine.SGI.4.05.9902211103430.9889-100000>