CDP or Cisco Discovery Protocol is enable by default on Cisco routers, CDP can be disabled either globally (stops advertisements on all interfaces) or partially by disabling advertisements on specific interface(s).
Disable CDP Globally
R1# configure terminal R1(config)# no cdp run
Disable CDP on Specific Interface
R1# configure terminal R1(config)# interface fa0/0 R1(config-if)# no cdp enable
Changed your mind, that’s ok you can re-enable CDP.
R1(config)# cdp run
CDP is usually disable due to security reasons people don’t like to advertise more than they have to, another good reason is CDP happens to be Cisco proprietary if the device on the other side of the interface is not Cisco then there is no reason for CDP to be running in the first place.
Feel free to leave a comment below, who knows I maybe able to provide some extra assistance.