CISCO specialized protocol CDP

1. CDP is a Cisco proprietary protocol and can only find information about directly connected devices.
2. Cisco routers send CDP updates on all interfaces by default. The default Update time is 60 s and the retention time is 180 s.
3. CDP messages are encapsulated in the header and tail of the data link layer. Without any layer-3 protocol, the data link layer must support the subnet Access Protocol (SNAP) header. Currently, most protocols support SNAP, such as Ethernet, hdlc, PPP, and frame relay.
4. CDP is enabled by default in global mode.
CDP commands:
Show cdp display CDP Update Time and Retention Time
Show cdp neighbors displays the neighbor information of each interface
Show cdp interface shows the status of each CDP interface enabled
Show cdp traffic display CDP broadcast quantity statistics
Show cdp counters
Debug cdp packets
 
Enable and disable CDP
Global start: CDP RUN
Close: NO CDP RUN
Interface startup and Shutdown
CDP ENABLE
NO CDP ENABLE
Set CDP Update Time and retention time globally
CDP TIMER
CDP HOLDTIME

Author: "xuemeng's blog"