1. IST 202
Chapter 4

2. Cisco Discovery Protocol (CDP)
Used to learn about directly connected Cisco routers & switches – neighbors
types of devices connected
interfaces used for the connections
model # s of the connected devices
Layer 2 protocol
small frame collects a lot of info
Media independent
Protocol independent
Proprietary protocol
only runs on Cisco devices
Runs over SNAP – subnetwork access protocol

3. Versions
CDP v1
Enabled by default on devices running IOS v10.3 or later
CDP v2
IOS v12 + supports

4. Network IP IPX
Data link CDP
Media LANs Frame ATM …
Supporting Relay
SNAP

5. How It Works Device boots CDP starts automatically
Detects neighbors running CDP (even if routers are running diff network protocols)
Each device running CDP sends out advertisements periodically

6. CDP Advertisements
at least one address at which it can receive SNMP messages
TTL information
blocks of info
TLV- Type Length Values
device id
interface
hold time
capability
platform
port id
VTP Mgmt Domain Name
Native VLAN
Full/half duplex

7. CDP Run Command
globally enables CDP (this is the default for IOS10.3+)
must be in global config mode
no CDP run to turn off

8. CDP Enable/Command CDP is disabled on interfaces by default
Enables CDP on an individual interface
Must be in interface config mode
No CDP enable to turn off

9. Clear CDP Counters Resets traffic counters to zero
Must be in privileged mode

10. Show CDP Displays intervals of advertisements TTL for given port
Advertisement version
May be in user or privileged mode

11. Show CDP Entry {entry name [protocol version] }
Displays info about a given neighbor
Can be limited to a protocol or version
Can be in user or privileged exec mode

12. Show CDP Interface [type & number]
Displays info about interfaces on which CDP is running
User or priv mode

13. Show CDP Neighbors [type & number] [detail]
Displays info about all neighbor devices running CDP
Detail – provides additional info
VLAN ID
Duplex mode
VTP domain name
User or Priv modes

14. Troubleshooting CDP
Table on p 620
Labs 4.1.4
4.1.6