cdp run and cdp enable in ODR Lab

Hi Guys,

I did the ODR lab and I understand that we need to use CDP enable under the tunnel interface to make ODR work.


But my question is since cdp run has already globally configured by default and is supposed to be applied automatically to all interfaces, why should we use "cdp enable" under the tunnel interface again? Why the global "cdp run"  is not applied under the tunnel interface while the other interfaces seems inherented.


Thank you!


  • Hi - bit late in adding to the post but hopefully helps illustrate for anyone reading later.

    After reading the previous posts I wanted to see what it looked like. Taken from an old GNS3 lab for tunnelling it doesn't have any cdp configuration so any settings are default.  It shows the default is for cdp only to be enabled on physical interfaces:

    R4#sho ip int br
    Interface              IP-Address      OK? Method Status                Protocol
    FastEthernet0/0      YES NVRAM  up                    up
    FastEthernet0/1  YES NVRAM  up                    up
    Loopback0       YES NVRAM  up                    up
    Tunnel0               YES NVRAM  up                    up
    Tunnel1               YES NVRAM  up                    up                              

    R4#sh cdp interface
    FastEthernet0/0 is up, line protocol is up
     Encapsulation ARPA
     Sending CDP packets every 60 seconds
     Holdtime is 180 seconds
    FastEthernet0/1 is up, line protocol is up
     Encapsulation ARPA
     Sending CDP packets every 60 seconds
     Holdtime is 180 seconds

    Also I vaguely remember a class lecturer discussing security and saying tunneling has cdp disabled by default.  His explanation being that from a security point of view you know your physical neighbours but tunnels (without any security) could in theory go anywhere and should be treated with caution.

Sign In or Register to comment.