# Cisco Discovery Protocol

CDP is a Cisco proprietary protocol.

It is enabled on Cisco devices (routers, switches, firewalls, IP phones, etc) by default.

CDP messages are periodically sent to multicas MAC address 0100.0CCC.CCCC.

When a device receives a CDP message, it processes and discards the message. It **does not** forward it to other devices.

By default, CDP messages are sent once every **60 seconds**.

By default, the CDP holdtime is **180 seconds**. If a message isn't received from a neighbor for 180 seconds, the neighbor is removed from the CDP neighbor table.

CDPv2 messages are sent by default.

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## CDP `show` command summary

1. Shows basic information about CDP (timers, version).

```
R1# show cdp
```

2. Displays how many CDP messages have been sent and received.

```
R1# show cdp traffic
```

3. Displays which interfaces CDP is enabled on.

```
R1# show cdp interface
```

4. Lists CDP neighbors and some basic information about each neighbor.

```
R1# show cdp neighbors
```

5. Lists each CDP neighbor with more detailed information.

```
R1# show cdp neighbors detail
```

6. Displays the same infor as above, but for the specified neighbor only.

```
R1# show cdp entry <name>
```

## CDP configuration commands

* CDP is globally enabled by default.
* CDP is also enabled on each interface by default.
* To enable/disable CDP globally: `R1(config)# [no] cdp run`
* To enable/disable CDP on specific interfaces: `R1(config-if)# [no] cdp enable`
* Configure the CDP timer: `R1(config)# cdp timer <seconds>`
* Configure the CDP holdtime: `R1(config)# cdp holdtime <seconds>`
* Enable/disable CDPv2: `R1(config)# [no] cdp advertise-v2`

## Wireshark capture

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