What NIC is my Virtual Server using?

We had a few network issues with a client site recently which meant that we had to perform some port mirroring to understand what was happening on the VMware side.  We didn’t have the luxury of Enterprise Plus licensing so couldn’t use the inbuilt port mirror features.  So it was manual time on the switch.

Most, if not all vSphere environment have redundancy built into them, with at least two uplinks (physical NIC’s) to the LAN.  They normally have ‘Route based on the originating virtual port ID’ as the load balancing policy. So vSphere uses an algorithm which states if I have 10 VM’s, then I will place 5 on each uplink.

So the question is, if I’m trying to perform some port mirroring on my Cisco/HP switch, which port should I mirror?

This is when we use esxtop.  First of all we need to login to the ESXi Host which is responsible for the Virtual Server using SSH.

Once in we run the command as follows:

esxtop (press enter)
n (press enter)

We now see which Virtual Servers are on which uplink (physical NIC)

ESXTOP

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