VMware Cloud Community
doljira
Contributor
Contributor

Tracing packet in ESXi using pktcap-uw

Hi all,

While tracing a packet inside ESXi 6.0 host using pktcap-uw, the packet from a VM on the host to the uplink passes the following paths

12:58:49.760069[1] Captured at PktFree point, TSO not enabled, Checksum offloaded and not verified, capture length 24 of 74.

  PATH:

   +- [12:58:49.759976] | VnicTx

   +- [12:58:49.759976] | PortInput

   +- [12:58:49.759981] | IOChain

   +- [12:58:49.759985] | EtherswitchDispath

   +- [12:58:49.759986] | EtherswitchOutput

   +- [12:58:49.759986] | PortOutput

   +- [12:58:49.759987] | IOChain

   +- [12:58:49.760000] | UplinkSndKernel

   +- [12:58:49.760001] | UplinkSnd

   +- [12:58:49.760068] | PktFree

I assume these trace points are function calls at different points in ESXi. As we can see from the trace,  time(PktFree)-time(UplinkSnd)= 57usec in this case and is always in the order 40-100 usec. Can someone explain me

what happens to the packet after UplinkSnd is called. Is the packet already in TX-ring of NIC or sent out on the wire?  What is PktFree? Does it mean, there will not be any reference to the packet in the hypervisor after this function is called?   Is there packet queuing after UplinkSnd is called?

What is IOChain ? Is it a function in vSwitch or vmkernel?

What does Checksum offloaded and not verified means?

Thanks,

Reply
0 Kudos
0 Replies