Hello,

With UDP tunnel segmentation offload feature, it is possible to send large (TSO) packets encapsulated by either Vxlan or Geneve. With such udp encapsulation, the outer checksum can either be 0 or offloaded to the nic to calculate (i.e. pseudo checksum populated).

My question - Is there any field in skb or any api which can let the nic know if the outer checksum is offloaded or not? We can always parse the header to udp and then check if its 0 or not, but I feel this is some sort of hack. So, I wanted to know if there is any API in linux stack through which I can get to know if the outer checksum is offloaded or not?

Any help is appreciated.

Thanks

You can use ethtool to toggle offloading feature.

Thanks for your reply. However, what you suggested relates to how we can enable/disable offloading feature. Even if we enable the offloading feature, user can specify if udp csum is required or not in outer header when vxlan interface is created. If vxlan interface is created with noudpcsum option, then the outer header wil have udp csum as 0.

So, my question is, how do we know if outer checksum is 0 or offload via skb or any other api?

Thanks

If so, you might have to look into kernel netfilter hook and NIC driver.