Switch discovery protocols allow vSphere administrators to determine which switch port is connected to a given vSphere standard switch or vSphere distributed switch.
vSphere supports Cisco Discovery Protocol (CDP) developed by Cisco and Link Layer Discovery Protocol (LLDP) Vendor Neutral.
CDP is available for vSphere standard switches and vSphere distributed switches connected to Cisco physical switches.
LLDP is available for vSphere distributed switches version 5.0.0 and later.When CDP or LLDP is enabled for a particular vSphere distributed switch or vSphere standard switch, you can view properties of the peer physical switch such as device ID, software version, and timeout from the vSphere Client.
Modes of Operation:
Listen: Esxi provides the information about the associated Physical Switch port.
Advertise: Esxi provides the information about the Virtual Switch to network admins.
Both: Esxi detects and displays the information about the Physical Switch and also provides the information of Virtual Switch to physical switch administrator.
For More Information Refer CDP and LLDP