NCS IOS-XR Trunk Interface CDP configuration

[adrian.bosshard]

Hello community,

How do I have to configure CDP on a trunk interface on an NCS540 with IOS-XR?

I have added the command "cdp" under the phisical Interface, but it wasn't successful :(

interface GigabitEthernet0/0/0/13
cdp
speed 1000
negotiation auto
!
interface GigabitEthernet0/0/0/13.12 l2transport
encapsulation dot1q 12
rewrite ingress tag pop 1 symmetric
!
interface GigabitEthernet0/0/0/13.13 l2transport
encapsulation dot1q 13
rewrite ingress tag pop 1 symmetric
!

Thanks for your feedback

[keanej]

I think the issue is that CDP on trunked interfaces are tagged. 

"CDP, VTP, and PAgP updates are always forwarded on trunks with a VLAN 1 tag. This is the case even if VLAN 1 has been cleared from the trunks and is not the native VLAN. Clearing VLAN 1 for user data has no impact on control plane traffic that is still sent using VLAN 1."

An easy way to get round this is to create a subinterface with tag one on either side - enable CDP on this and everything should work.

interface GigabitEthernet0/0/0/13.1
encapsulation dot1q 1

cdp enable

FYI - Im not sure why you are hard setting the speed to 1000 - normally this is set to auto.

- maybe there is some hardware compatiabliliy issue - but I wouldnt do that unless I had to.

[adrian.bosshard]

Thanks for your feedback.

Well I have changed the interface settings to auto negotiation, just to exclude any other problems.

I also have added the default vlan on the trunk configuration, and also allowed the vlan 1 on the opposite device.

interface GigabitEthernet0/0/0/13
cdp
!
interface GigabitEthernet0/0/0/13.1 l2transport
encapsulation dot1q 1
rewrite ingress tag pop 1 symmetric
!
interface GigabitEthernet0/0/0/13.12 l2transport
encapsulation dot1q 12
rewrite ingress tag pop 1 symmetric
!
interface GigabitEthernet0/0/0/13.13 l2transport
encapsulation dot1q 13
rewrite ingress tag pop 1 symmetric
!

But I still dosen't get the cdp neighbor ship working :(

I only can enable cdp on the pfysical interface, not on the sup-interface.

RP/0/RP0/CPU0:PE1#sh cdp interface gigabitEthernet 0/0/0/13
Tue Sep 17 10:04:52.448 UTC
GigabitEthernet0/0/0/13 is Up
Encapsulation ether
Sending CDP packets every 60 seconds
Holdtime is 180 seconds
RP/0/RP0/CPU0:PE1#

any idea?