From mboxrd@z Thu Jan 1 00:00:00 1970 From: Glen Turner Subject: DHCP and jumbo frames Date: Mon, 06 Sep 2004 13:49:29 +0930 Sender: netdev-bounce@oss.sgi.com Message-ID: <1094444369.22662.32.camel@andromache> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: To: netdev@oss.sgi.com Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org Hi folks, I'm trying to make DHCP work correctly for ethernet jumbo frame media and jumbo+standard MTU subnets on jumbo media. It's turning into a bit of a long slog (RFC amendments, etc), but jumbo frames will never seen widespread host deployment without it. It turns out that the DHCP client has to be able to select from a range of potential DHCP offers (all else equal it should select the offer with the largest MTU) and has to be able to reject an offer with an MTU the hardware cannot support. Setting the MTU often re-sets the ethernet controller (as far as I can tell from the e1000 source). So checking each DHCP offer by attempting to write the MTU to the hardware isn't going to work well. Especially if an ethernet controller reset causes the PHY to drop carrier, as spanning tree hold-downs could then cause the DHCP state machine to time out. Is there any way for the DHCP client to query every interface for the MTU size ranges that the interface supports? Advice is very appreciated, Glen -- Glen Turner Tel: (08) 8303 3936 or +61 8 8303 3936 Australia's Academic & Research Network www.aarnet.edu.au