How CDP (Cisco Discovery Protocol) will benefit you to identify *** Which NIC connected to what External Device on ESX ***

Source : VMware KB and www.vmetc.com 
 

This is a handy little trick, starting with version 3.5, VMware added support for Cisco Discovery Protocol (CDP) on the ESX Server vSwitches. CDP support is enabled on a vSwitch with this command:

Verify the current CDP setting for vSwitch2
ESX# esxcfg-vswitch -b vSwitch2 

down 

The above output is down - which indicates CDP is currently not enabled vSwitch2  

To enable CDP on vSwitch2

ESX# esxcfg-vswitch -B both vSwitch2

To Verify the CDP Status (Expect -> Down, Listen, Advertise, Both)

ESX# esxcfg-vswitch -b vSwitch2

Both

Check CDP information on Physical Switch

Once CDP support is enabled on the vSwitch & physical switch - execute below command on Phy.Switch. Which will show the link between each physical switch port and the matching ESX Server NIC. The output will look something like this:

# show cdp neighbor 

 Capability Codes: R-Router, T-Trans Bridge, B-Source Route Bridge

                  S-Switch, H-Host, I-IGMP, r-Repeater, P-Phone

DeviceID  Local Intrfce  Holdtme  Capability  Platform      Port ID

s3        Gig   0/26        147      T S    WS-C3524-XFas 0/24

esx04     Gig   0/22        168       S     VMware        ESXvmnic0

esx04     Gig   0/21        168       S     VMware        ESXvmnic1

As you can see in the output above, the CDP output clearly links the physical switch port and the ESX Server NIC. This makes it incredibly easy to identify the NICs in the server. This is particularly helpful in blade situations, since you can’t exactly unplug the NIC and see which one goes down with “esxcfg-nics -l” (a common approach to identifying the NICs in the server). Of course, this requires CDP switches in the blade chassis. Since the internal port mappings on the blade chassis determine which NICs connect to which ports, this command adds the mapping within ESX Server and lets us quickly and definitively identify the NICs in the server as seen by ESX Server.

Check CDP information in VI Client

Now, using the VI Client you can go to the Configuration tab of a host and select Networking. To the right of each vSwitch is what I’ll describe as a dialogue icon.

Clicking this Call out icon (Green circle) brings up the switch port info you are seeking.