Defending Network Switches
CDP security issues

Attackers with knowledge of how Cisco Discovery Protocol (CDP) works could find ways to take advantage of the clear text CDP packets to gain knowledge of edge of the network. The CDP runs at Layer 2 and allows Cisco devices to identify themselves to other Cisco devices. However, the information sent through CDP is transmitted in clear text and unauthenticated. Utilizing a packet analyzer, attackers could glean information about the network device from CDP advertisements.  – 

CDP is necessary for management applications and cannot be disabled without impairing some network-management applications. However, CDP can be selectively disabled on interfaces where management is not being performed.