[Day 6] 2. CDP (Cisco Discovery Protocol)

CDP is preinstalled on all Cisco devices and is used to discover information about directly connected Cisco devices.
CDP sends packets every 60 seconds by default to share information about neighbors.

A#show cdp neighbor:
- Displays a list of directly connected Cisco devices, including switches and routers, along with key parameters such as the platform, local interface, and device ID.
- Note: This feature is exclusive to Cisco devices.
A#show cdp neighbor detail:
- Provides detailed, vertically formatted information about the neighbor devices, including the IOS version and IP address.

CDP messages are generated every 60 seconds.
The Hold Down Timer is set to 180 seconds.
- The CDP table refreshes each time an announcement is received from a neighbor, and the hold timer is reset.
- If no announcements are received from a device within the hold time (180 seconds), the device information is removed from the CDP table.

To disable CDP globally:
- ```
A(config)# no cdp run
```
To disable CDP on a specific interface:
- ```
A(config-if)# no cdp enable
```
To change the CDP packet timer (how often CDP packets are sent):
- ```
A(config)# cdp timer <seconds>
```
  - Example:
```
A(config)# cdp timer 90
```
    (sends packets every 90 seconds).
To change the hold time (how long CDP information is retained in the table):
- ```
A(config)# cdp holdtime <seconds>
```
  - Example:
```
A(config)# cdp holdtime 270
```
    (sets hold time to 270 seconds).