CDP Not Detected

[hs08]

I have topology as attached picture, and want to know why R3 cannot detect CDP R4?

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R3 can detect CDP R1 but not detect CDP R4

R2 can detect CDP R1 and also CDP R4

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[M02@rt37]

Hello @hs08 

The link between R3 and R4 is up ?

Check the interface configurations on both R3 and R4 to ensure that they are configured correctly and that the interface status is up/up.

If the physical connection and interface configurations are correct, you may need to check the CDP configurations on both devices (in global mode not only on interfaces). CDP is a layer 2 protocol that allows devices to share information about their connected neighbors, so it is important to ensure that CDP is enabled and configured correctly on all devices in the network.

[hs08]

Hello,

Link between R3 and R4 is up and CDP is enabled for both interface

[M02@rt37]

Hello @hs08 

Between R3 and R4 is WAN Link? 

Are there any operator equipement between R3 and R4 ? Is it a LAN To LAN ? Is it a Black Fiber? 

Between your others routers, is it a WAN link too?

[hs08]

Hello M02@rt37 

Link between R3 - R4 is WAN and R2 - R4 also WAN. Both WAN using different provider / operator.

I'm not sure if on WAN connection the provider have any equipment or not.

[M02@rt37]

@hs08 

You confirm that cdp is enable on interfaces on each routers.

Then, perhaps with this WAN operator link you have an operator router in front of R3 and R4. In this case, impossible to have cdp protocol between R3 and R4 because there are not directly connected.

[hs08]

HI M02@rt37 

Yes, maybe that one reason why CDP not detected.

[MHM Cisco World]

in global you do 

CDP run 
in interface 
cdp enable 

[hs08]

Hello,

Already enabled but still not detected. Connection from R3 to R4 using WAN, and i already ask to the provider is there any filtering on their side but they say no any filtering.

[MHM Cisco World]

WAN can drop the CDP packet 
do 
debug cdp packets <<- check if the router send/receive CDP packet