CKO and MAC Forwarding

[Juan González]

Hi,

I am testing the MAC forwarding load balancer software included in the Websphere Application Server Edge Components over HP-UX 11i.

This software fails over Gigabit NICs, but works correctly over 10/100 NICs.

I suspect that maybe there is a negative interaciont between the kernel module installed by the software and the Checksum Offload feature of the NIC. The kernel module main function is avoid certain packets (the ones that must be load balanced, for example those directed to some port) reach the TCP/IP stack and MAC-forwarding them to the chosen server.

Does anybody suspect why can be going wrong?
Maybe master rick jones?

Thanks in advance.

Best regards,
Juan

[rick jones · Accepted solution]

You rang?-)

I didn't know that websphere had in-kernel components... how, well, clever of them...

But it seems not quite clever enough - I do have recollections of there being issues with Resonate Load balancing in the 'way back when' with gigabit and CKO. I'm not sure that they were ever resolved before that company went most of the way of all things.

I do not recall if we ever put-in a switch to disable CKO. I suppose a search in the knowledge bases might find something.

Longer term, the websphere folks will have to excercise their HP ISV support contacts and get the knowledge of how to properly deal with CKO in HP-UX. It might be something as simple as stripping-off the leading CKO mblk before trying to forward the packet back out the NIC(s). Then again, it might not. I've not looked at detailed code there in a long time.

[Xianjie Zhang]

If the kernel module of Websphere sits above DLPI/driver, it must insert/reserve some CKO fields in the packet sent to gigabit driver. The kernel module also needs to set some flags for the packet if it does not want drivers to do CKO.

[Jay Kidambi]

Juan,

The following document has detailed information about CKO implementation on HP-UX 11i.

http://h21007.www2.hp.com/dspp/files/unprotected/Drivers/Docs/TechPapers/cko_wlicense.pdf

Jay