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This chapter describes how to configure the Cisco Discovery Protocol (CDP) on the Catalyst 6000 family switches.
This chapter consists of these sections:
CDP is a media- and protocol-independent protocol that runs on all Cisco-manufactured equipment including routers, bridges, access and communication servers, and switches. Using CDP, you can view information about all the Cisco devices directly attached to the switch. In addition, CDP detects native VLAN and port duplex mismatches.
Network management applications can retrieve the device type and SNMP-agent address of neighboring Cisco devices using CDP. This enables applications to send SNMP queries to neighboring devices. CDP allows network management applications to discover Cisco devices that are neighbors of already known devices, in particular, neighbors running lower-layer, transparent protocols.
CDP runs on all media that support Subnetwork Access Protocol (SNAP). CDP runs over the data link layer only.
Cisco devices never forward CDP packets. When new CDP information is received, Cisco devices discard old information.
Table 23-1 shows the default CDP configuration.
| Feature | Default Value |
|---|---|
CDP global enable state | Enabled |
CDP port enable state | Enabled on all ports |
CDP message interval | 60 seconds |
CDP holdtime | 180 seconds |
These sections describe how to configure CDP:
To set the CDP global enable state, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Set the CDP global enable state on the switch. | set cdp {enable | disable} |
Step 2 Verify the CDP configuration. | show cdp |
This example shows how to enable CDP globally and verify the configuration:
Console> (enable) set cdp enable CDP enabled globally Console> (enable) show cdp CDP : enabled Message Interval : 60 Hold Time : 180 Console> (enable)
This example shows how to disable CDP globally and verify the configuration:
Console> (enable) set cdp disable CDP disabled globally Console> (enable) show cdp CDP : disabled Message Interval : 60 Hold Time : 180 Console> (enable)
You can enable or disable CDP on a per-port basis. You must enable CDP globally before the switch will transmit CDP messages on any ports.
To change the CDP enable state on a per-port basis, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Set the CDP enable state on individual ports. | set cdp {enable | disable} [mod_num/port_num] |
Step 2 Verify the CDP configuration. | show cdp port [mod_num[/port_num]] |
This example shows how to disable CDP on ports 3/1-6 and verify the configuration:
Console> (enable) set cdp disable 3/1-6 CDP disabled on ports 3/1-6. Console> (enable) show cdp port 3 CDP : enabled Message Interval : 60 Hold Time : 180 Port CDP Status -------- ---------- 3/1 disabled 3/2 disabled 3/3 disabled 3/4 disabled 3/5 disabled 3/6 disabled 3/7 enabled 3/8 enabled 3/9 enabled 3/10 enabled 3/11 enabled 3/12 enabled Console> (enable)
This example shows how to enable CDP on ports 3/1-2 and verify the configuration:
Console> (enable) set cdp enable 3/1-2 CDP enabled on ports 3/1-2. Console> (enable) show cdp port 3 CDP : enabled Message Interval : 60 Hold Time : 180 Port CDP Status -------- ---------- 3/1 enabled 3/2 enabled 3/3 disabled 3/4 disabled 3/5 disabled 3/6 disabled 3/7 enabled 3/8 enabled 3/9 enabled 3/10 enabled 3/11 enabled 3/12 enabled Console> (enable)
The CDP message interval specifies how often the switch will transmit CDP messages to directly connected Cisco devices.
To change the default CDP message interval, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Change the default CDP message interval. The allowed range is 5-900 seconds. | set cdp interval interval |
Step 2 Verify the CDP configuration. | show cdp |
This example shows how to change the default CDP message interval to 100 seconds and verify the configuration:
Console> (enable) set cdp interval 100 CDP message interval set to 100 seconds for all ports. Console> (enable) show cdp CDP : enabled Message Interval : 100 Hold Time : 180 Console> (enable)
The CDP holdtime specifies how much time can pass between CDP messages from neighboring devices before the device is no longer considered connected and the neighbor entry is aged out.
To change the default CDP holdtime, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Change the default CDP holdtime. The allowed range is 10-255 seconds. | set cdp holdtime interval |
Step 2 Verify the CDP configuration. | show cdp |
This example shows how to change the default CDP holdtime to 225 seconds and verify the configuration:
Console> (enable) set cdp holdtime 225 CDP holdtime set to 225 seconds. Console> (enable) show cdp CDP : enabled Message Interval : 100 Hold Time : 225 Console> (enable)
To display information about directly connected Cisco devices, use the show cdp neighbors command. Use the vlan keyword to display the native VLAN for the connected ports. Use the duplex keyword to display the duplex mode for the connected ports. Use the capabilities keyword to display the device capability codes for the connected device. Use the detail keyword to display detailed information about the neighboring device.
To display information about directly connected Cisco devices:
| Task | Command |
|---|---|
View information about CDP neighbors. | show cdp neighbors [mod_num[/port_num]] [vlan | duplex | capabilities | detail] |
This example shows how to display CDP neighbor information for connected Cisco devices:
Console> (enable) show cdp neighbors * - indicates vlan mismatch. # - indicates duplex mismatch. Port Device-ID Port-ID Platform -------- ------------------------------- ------------------------- ------------ 2/3 JAB023807H1(2948) 2/2 WS-C2948 3/1 JAB023806JR(4003) 2/1 WS-C4003 3/2 JAB023806JR(4003) 2/2 WS-C4003 3/5 JAB023806JR(4003) 2/5 WS-C4003 3/6 JAB023806JR(4003) 2/6 WS-C4003 Console> (enable)
This example shows how to display the native VLAN for each port connected on the neighboring device (there is a native VLAN mismatch between port 3/6 on the local switch and port 2/6 on the neighbor device, as indicated by the asterisk [*]):
Console> (enable) show cdp neighbors vlan * - indicates vlan mismatch. # - indicates duplex mismatch. Port Device-ID Port-ID NativeVLAN -------- ------------------------------- ------------------------- ---------- 2/3 JAB023807H1(2948) 2/2 522 3/1 JAB023806JR(4003) 2/1 100 3/2 JAB023806JR(4003) 2/2 100 3/5 JAB023806JR(4003) 2/5 1 3/6 JAB023806JR(4003) 2/6* 1 Console> (enable)
This example shows how to display detailed information about the neighboring device:
Console> (enable) show cdp neighbors 2/3 detail Port (Our Port): 2/3 Device-ID: JAB023807H1(2948) Device Addresses: IP Address: 172.20.52.36 Holdtime: 132 sec Capabilities: TRANSPARENT_BRIDGE SWITCH Version: WS-C2948 Software, Version McpSW: 5.1(57) NmpSW: 5.1(1) Copyright (c) 1995-1999 by Cisco Systems, Inc. Platform: WS-C2948 Port-ID (Port on Neighbors's Device): 2/2 VTP Management Domain: Lab_Network Native VLAN: 522 Duplex: full Console> (enable)
Posted: Wed Nov 10 13:06:33 PST 1999
Copyright 1989-1999©Cisco Systems Inc.