UDLD agressive mode configured but interface is not put in errdisable mode

Unanswered Question
May 13th, 2009

Hi all,

I have a strange problem here (or at least I think it’s strange)..

I’m using one WS-C2960-24TC-L and a WS-C2960-48TC-L running 12.2(44)SE1 software version.

I configured an etherchannel between those two devices using multimode fiber and GLC-FE-100FX connectors. I have two interfaces being part of this etherchannel .

At the beginning, I didn’t configured UDLD and I had the following behavior:

- I can disconnect one connector at the time (the RX or the TX), on one of the switches and I still have connectivity between the devices. I found some information that this is because this software version and this particular SFP connector has Far End Fault Indication capability.

I moved on and load the 12.2(50)SE software version on one of the devices. Then I got the following behavior:

- When I disconnect the RX or the TX from the first fiber link (on the 12.2(50)SE device) => no connectivity between the devices;

- When I disconnect the RX or the TX from the second fiber link I do have connectivity between the devices.

So what I imagined is that, Far End Fault Indication is not supported on this software version (even if there was a known issue related to this and it is supposed to be solved starting from the 12.2 (37)SE release) and I tried to configure “udld aggressive” as workaround. I globally enabled UDLD but there was no change in the behavior : the link was DOWN at one end ant it was still UP at the other end like UDLD didn’t even exist. Here below is the output of the “show udld Gi0/1” on one side :

Interface Gi0/1

---

Port enable administrative configuration setting: Enabled / in aggressive mode

Port enable operational state: Enabled / in aggressive mode

Current bidirectional state: Unknown

Current operational state: Advertisement

Message interval: 7

Time out interval: 5

No neighbor cache information stored

On the other side, the link was down but the interface was not put in errdisable => there was no connectivity between the devices.

I reinstalled the 12.2(44)SE1 on both switches and let the udld activated. This time, the faulty link was DOWN on both ends (so I had connectivity between the devices via the other link) but the faulty interface was not put in errdisable.

Did anyone already encounter this kind of behavior or I’m missing something somewhere.

It looks like the 12.2(44)SE1 works fine even if UDLD is not enabled. So there must be the Far End Fault capability doing the job….. ? But again, why the interface is not put in errdisable state ?

As for the 12.2(50)SE software version , this is not working even if UDLD is enabled ?

Thanks.

Regards,

Mary

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Giuseppe Larosa Wed, 05/13/2009 - 12:21

Hello Mary,

>> No neighbor cache information stored

UDLD also in aggressive mode puts a port in errordisable if an UDLD capable neighbor was on the link.

the above line tells that no neighbor has been detected and so UDLD doesn't react.

So the question becomes if UDLD was actually enabled on the other side or not.

if UDLD was enabled there is a problem a lack of support on this GLC-FE-100FX.

Otherwise you may need to enable UDLD explicitly on the interface.

Hope to help

Giuseppe

tumbulina Thu, 05/14/2009 - 00:17

Hi Giuseppe,

The UDLD was enabled on the other link and when eveything is ok (the fibers are well connected), we can see that UDLD is "seeing" the other device connected on the link :

Interface Gi0/1

---

Port enable administrative configuration setting: Enabled / in aggressive mode

Port enable operational state: Enabled / in aggressive mode

Current bidirectional state: Bidirectional

Current operational state: Advertisement - Single neighbor detected

Message interval: 15

Time out interval: 5

Entry 1

---

Expiration time: 34

Device ID: 1

Current neighbor state: Bidirectional

Device name: xxxx

Port ID: Gi0/1

Neighbor echo 1 device: yyyy

Neighbor echo 1 port: Gi0/1

Message interval: 15

Time out interval: 5

CDP Device name: Switch

Switch#show udld gigabitEthernet 0/2

Interface Gi0/2

---

Port enable administrative configuration setting: Enabled / in aggressive mode

Port enable operational state: Enabled / in aggressive mode

Current bidirectional state: Bidirectional

Current operational state: Advertisement - Single neighbor detected

Message interval: 15

Time out interval: 5

Entry 1

---

Expiration time: 40

Device ID: 1

Current neighbor state: Bidirectional

Device name: xxxx

Port ID: Gi0/2

Neighbor echo 1 device: yyyy

Neighbor echo 1 port: Gi0/2

Message interval: 15

Time out interval: 5

CDP Device name: Switch

So, we have two situations :

- both devices using 12.2(44)SE1 with or without UDLD configuration, the connectivity is not lost if the RX or TX of one of the fibers is unplugged. And again no errdisable interface.

- one device is in 12.2(50)SE version and there, connectivity is lost when the RX or the TX is unplugged for the fist fiber (Gi0/1 to Gi0/1). So I imagine that the first link of the channel is used to communicate between the devices because when I unplugged the RX or the TX from the second link, I do have connectivity.

In this case, even with UDLD enabled, the ports of the first link are not going down so the devices still try to communicate via this link.

Like I said, there is a bug (CSCsh70266) related to GLC-FE-100FX not supporting the Far-End Fault Indication but it should be fixed starting from the 12.2(37)SE version. And the workaround for this bug is configuring agressive UDLD ...

So don't really see what this could be. I also tried to configure the UDLD under the interfaces but the result is the same.

Regards,

Mary

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