实验环境：Packet Tracert 5.0
实验设备：2621路由器两台，2960交换机两台
实验拓扑：
CDP（Cisco Discovery Protocol）思科发现协议，用来获取直连设备的一些基本信息，如设备平台，直连接口类型等。
在任一设备上输入：
routerA#show cdp
Global CDP information:
Sending CDP packets every 60 seconds
Sending a holdtime value of 180 seconds
Sending CDPv2 advertisements is enabled
Global CDP information:
Sending CDP packets every 60 seconds
Sending a holdtime value of 180 seconds
Sending CDPv2 advertisements is enabled
从上面的输出可以看出：
1.CDP包每60s发送一次。
2.CDP保持计时器是180s，超过这个时间就认为邻居失效。
3.默认启用的是CDPv2。
在Router3上输入：
routerA# show cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone
Device ID Local Intrfce Holdtme Capability Platform Port ID
routerB Fas 0/0 149 R C2600 Fas 0/0
siwtchA Fas 0/1 157 S 2960 Fas 0/1
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone
Device ID Local Intrfce Holdtme Capability Platform Port ID
routerB Fas 0/0 149 R C2600 Fas 0/0
siwtchA Fas 0/1 157 S 2960 Fas 0/1
从上面的输出可以看出：
此设备有两台直连设备，routerB 和siwtchA，直连设备的相关信息也显示出来了。
在Router3上输入：
routerA#show cdp entry *
Device ID: routerB
Entry address(es):
Platform: cisco C2600, Capabilities: Router
Interface: FastEthernet0/0, Port ID (outgoing port): FastEthernet0/0
Holdtime: 141
Entry address(es):
Platform: cisco C2600, Capabilities: Router
Interface: FastEthernet0/0, Port ID (outgoing port): FastEthernet0/0
Holdtime: 141
Version :
Cisco Internetwork Operating System Software
IOS (tm) C2600 Software (C2600-I-M), Version 12.2(28), RELEASE SOFTWARE (fc5)
Technical Support: [url]http://www.cisco.com/techsupport[/url]
Copyright (c) 1986-2005 by cisco Systems, Inc.
Compiled Wed 27-Apr-04 19:01 by miwang
Cisco Internetwork Operating System Software
IOS (tm) C2600 Software (C2600-I-M), Version 12.2(28), RELEASE SOFTWARE (fc5)
Technical Support: [url]http://www.cisco.com/techsupport[/url]
Copyright (c) 1986-2005 by cisco Systems, Inc.
Compiled Wed 27-Apr-04 19:01 by miwang
advertisement version: 2
Duplex: full
---------------------------
Duplex: full
---------------------------
Device ID: siwtchA
Entry address(es):
Platform: cisco 2960, Capabilities: Switch
Interface: FastEthernet0/1, Port ID (outgoing port): FastEthernet0/1
Holdtime: 148
Entry address(es):
Platform: cisco 2960, Capabilities: Switch
Interface: FastEthernet0/1, Port ID (outgoing port): FastEthernet0/1
Holdtime: 148
Version :
Cisco IOS Software, C2960 Software (C2960-LANBASE-M), Version 12.2(25)FX, RELEASE SOFTWARE (fc1)
Copyright (c) 1986-2005 by Cisco Systems, Inc.
Compiled Wed 12-Oct-05 22:05 by pt_team
Cisco IOS Software, C2960 Software (C2960-LANBASE-M), Version 12.2(25)FX, RELEASE SOFTWARE (fc1)
Copyright (c) 1986-2005 by Cisco Systems, Inc.
Compiled Wed 12-Oct-05 22:05 by pt_team
advertisement version: 2
Duplex: full
Duplex: full
从上面的输出结果可以看出：
这条命令显示的信息要比show cdp neighbors 更详细。
在Router3上输入：
routerA#show cdp interface
FastEthernet0/0 is up, line protocol is up
Sending CDP packets every 60 seconds
Holdtime is 180 seconds
FastEthernet0/1 is up, line protocol is up
Sending CDP packets every 60 seconds
Holdtime is 180 seconds
routerA#show cdp interface
FastEthernet0/0 is up, line protocol is up
Sending CDP packets every 60 seconds
Holdtime is 180 seconds
FastEthernet0/1 is up, line protocol is up
Sending CDP packets every 60 seconds
Holdtime is 180 seconds
从上面的输出结果可以看出来：
显示了此设备上哪些接口开启了cdp协议。
在Router3上输入：
routerA(config)#no cdp run
routerA(config)#^Z
%SYS-5-CONFIG_I: Configured from console by console
routerA#show cdp interface
% CDP is not enabled
routerA(config)#^Z
%SYS-5-CONFIG_I: Configured from console by console
routerA#show cdp interface
% CDP is not enabled
从上面的输出结果可以看出：
全局配置模式下的no cdp run禁用了设备上所有接口的cdp协议。
在Router3上输入：
routerA(config)#int f0/1
routerA(config-if)#no cdp enable
routerA(config-if)#no cdp enable
上面的命令表示只在接口f0/1禁用cdp，其他接口仍然可以使用cdp。
注：必须要等待holdtime时间超时之后才能在show cdp neighbors 输出中看见与f0/1相连的邻居没有了。
如果在全局配置模式下禁用cdp的话，那么即使在接口配置模式下启用某个接口的cdp也是无效的。
