IST 202 Chapter 4
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
Versions CDP v1 Enabled by default on devices running IOS v10.3 or later CDP v2 IOS v12 + supports
Network IP IPX Data link CDP Media LANs Frame ATM … Supporting Relay SNAP
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
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
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
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
Clear CDP Counters Resets traffic counters to zero Must be in privileged mode
Show CDP Displays intervals of advertisements TTL for given port Advertisement version May be in user or privileged mode
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
Show CDP Interface [type & number] Displays info about interfaces on which CDP is running User or priv mode
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
Troubleshooting CDP Table on p 620 Labs 4.1.4 4.1.6