CDP neighbors question.

[dannan lin]

hi:

i have a question about CDP neighbors.

from the topology below

R3 and R2 using same IP addre to connect each other .

so when i run "show cdp neighbor" R2 can still discover the R3 .

how did R2 discover R3, that does not make much sense here since both router were configured as same IP.

is it because CDP is layer 1 protocol ?

thanks for your help.

[joeadiutori]

Perhaps a typo??  I dont think the 2 routers can have the same IP.

[Reza Sharifi · Accepted solution]

CDP is layer-2

have a look:

http://www.cisco.com/en/US/tech/tk962/technologies_tech_note09186a00801aa000.shtml

HTH

[dannan lin]

thank you guys.

[Kishore Chennupati]

Hi danna,

You are right when you say that you see the CDP information. the moment you bring up the interface and turn on CDP it starts talking on the multicast address.

In your case  the point here is that you will see the information on only 1 device that one that gets the ip address first and the other one will start complaining about the duplicate ip address.

So you are partly right.

HTH

Kishore