From: "Chris Friesen" Subject: Re: dhcp-based netboot over jumbo-frame network? Date: Wed, 08 Apr 2009 16:10:34 -0600 Message-ID: <49DD20DA.3020902@nortel.com> References: <49DCE470.9060109@nortel.com> <49DCF7E2.2060304@hp.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: linux-kernel@vger.kernel.org, Linux Network Development list To: Rick Jones Return-path: In-Reply-To: <49DCF7E2.2060304@hp.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Rick Jones wrote: > Chris Friesen wrote: >> We have an existing system that loads a bare kernel using tftp, then >> mounts a rootfs via NFS. The wrinkle is that this is on a jumbo-frame >> enabled network, so somehow the MTU needs to be set before mounting the >> rootfs. > > Why? Is the NFS mount not TCP? If it is TCP, then the TCP MSS exchange will > provide you cover as it will (should) cause TCP in the NFS server to segment to > the MSS option your system with the then-smaller MTU sends. > > I would think that only if the NFS mount is UDP that you would have a problem > with the system initially booting with a small MTU. Currently it uses the default, which is udp. I might be able to get them to try TCP. Thanks for the suggestion. >> In a previous version we patched ipconfig.c to support the DHCP option >> to specify the MTU value, but I'm wondering about the "proper" way to do >> this on current kernels. > > Was the change submitted to upstream and rejected? The change was submitted (not by us) back in the 2.6.10 timeframe, and was rejected with the suggestion to use initramfs. Chris