udld does not work on C9500-48Y4C.

[Electronic20]

Hello community:

I have a case, where the UDLD is not working, I have 2 switches at both remote ends and connected by 2-wire fiber.

Both switches have the QSFP-40G-ER4 transceiver and the following was configured on both ports on each end:

errdisable recovery interval 60

int HundredGigE2/0/25
switchport mode trunk
udld port aggressive
channel-group 40 mode active

The C9500-48Y4C switches have firmware 17.06.04

When I disconnect a thread the port goes down but it does not go into the err-disable state that should appear in the switch logs, but does not appear.

Why does it not appear to be that state? Could it be because of the C9500-48Y4C version? Could it be because it is associated with a portchannel? Would it be because of the transceiver? Or would some configuration be missing in said model and version of the equipment?

Please kindly support me with this case.

[MHM Cisco World]

What udld mode you run?

Aggresive mode errdisable port.

MHM

[Electronic20]

Hi @MHM Cisco World  

Is aggresive mode

[MHM Cisco World]

Both side use aggresive mode.

Ok' but there is also one factor here'

Port channel' portchannel with udld I think this behavior is normal'

One port member will down but the all port channel not go to errdisable.

Check this point.

MHM

[Electronic20]

Hi @MHM Cisco World 

If aggressive mode is on both sides, the settings on both sides are the same.

You do not want the port-chanel to be disabled, only the port HundredGigE2/0/25 on both ends are the same port and rtransceivers, but the err-disable mode does not appear when we disconnect only one fiber strand.

[MHM Cisco World]

https://community.cisco.com/t5/switching/udld-config/td-p/1785341

Check this link 

[balaji.bandi]

I have 2 switches at both remote ends and connected by 2-wire fiber.

both the side cat 9500 ? or what is other side ?

check the UDLD behavior and work in best way :

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst9500/software/release/16-8/configuration_guide/lyr2_lyr3/b_168_lyr2_9500_cg/b_168_lyr2_lyr3_9500_cg_chapter_0100.html

[Electronic20]

Hi @balaji.bandi 

​The same behavior appears at both ends, the err-disable log does not appear even in its interfaces.

[balaji.bandi]

both the sides Cat 9500 ?

before Fibre remove testing, is the UDLD neighbours you see ?

before and after remove fibre can you post below output :

show int HundredGigE2/0/25

show int HundredGigE2/0/25 trans

[Electronic20]

Hi @balaji.bandi 

appears on both sides.

The neighbors cannot be seen in UDLD, since when removing a thread the port on both sides is down, but since the ports on both sides are configured by UDLD and with the same configuration, the err-disable message should appear but it does not appear in the switch logs.

As an observation, the fiber has 2 wires, and only one wire is removed to validate the operation of the UDLD.

When the 2 threads that the fiber has are present, the port is in the up state, and when we remove the thread the port is in the down state. but the err-disable message does not appear, which should be the normal behavior of the UDLD.