dhcp-based netboot over jumbo-frame network?

Hi all,

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.

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.

I suppose the obvious answer would be initramfs. The downsides to that solution are that it would increase the size of the kernel file, and we would need to change the existing build system. In the face of a small patch to ipconfig, it's not a very attractive solution.

Looking forward to your responses.

Chris

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.

Was the change submitted to upstream and rejected?

rick jones

Currently it uses the default, which is udp. I might be able to get them to try TCP. Thanks for the suggestion.

The change was submitted (not by us) back in the 2.6.10 timeframe, and was rejected with the suggestion to use initramfs.

Chris