It’s possible to configure the ESX host's virtual switches so the Cisco Discovery Protocol on a standard or distributed switch is issuing broadcasts containing some of your ESX host's information. After enabling the CDP on your ESX server, the Cisco administrator is able to listen for information broadcasted by your ESX host but what can he actually see? To find out I’ve installed the Tallsoft’s Cisco CDP Monitor on my vCenter server.
With Cisco CDP Monitor, you can display the information of the connecting Cisco devices, such as device names, device models, connecting port , administrative ip address, IOS version, VTP Domain Name, and so on. With this information, one could easily learn the total topology of the complete network and do troubleshooting. Once the Cisco Discovery Protocol information changes (such as the link or device failed, or the setup of Cisco device changed), Cisco CDP Monitor will detect it and will display the related info. It also shows information broadcasted by you ESX servers.
Virtual switches can be configured for four different CDP modes of operation:
Down – CDP information is neither sent nor received
Listen – CDP information is received from the physical switches
Advertise – CDP information is sent to the physical switches
Both – CDP information is sent to and received from the physical switches
For enabling CDP on standard switches you have to use command-line interface. CDP can be enabled on distributed switches using the vSphere Client. Here’s the info I was able to retrieve from an ESX host after running “esxcfg-vswitch -B both vSwitch0” in the service console.
Neigbour1:
device id: esx4-l.ntpro.local
ipaddress: 0.0.0.0
port: vmnic0 
capabilities: Switch
ios_version: Releasebuild-208167
platform: VMware ESX
prefix:
vtp_domain:
native_vlan:
duplex: full
