Fibre cables connect the wrong way

[Andy White]

Hello,

I've not worked with fibre much, but we have had a remote switch added to a network and a new fibre link but can't see the switch, it is possible the fibre has been put in the wrong way round (tx/rx), is there any debugs I can do to prove this?

Thanks

[Jan Rolny]

Hi Andy,

i think here is not too much options how to discover if fiber was put into right rx/tx pair.

One thing which could help you is to configure UDLD on fiber port and see log if some syslog messages appears regarding UDLD.

Please see this page which describes UDLD:

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a008009477b.shtml

Best regards,

Jan

Please rate post if helpful

[paolo bevilacqua]

You cannot do any debug.

When the field technician connects the fiber, must check led on interface. If it doesn't lit, the work is not done correctly.

[manish arora]

Please have the Technician check the cable mode type as well as your Connector type. The multimode cable dont work on the single mode connectors on Cisco in past experience.

Manish

[jayson.sarausos]

Fastest way to check is to do physical check:

1. Check that you can see the red light from the fiber cable and determine if where you see the light, e.g Left or Right.

2. Check that you can see the red light from the the SFP connected to the switch and determine if where you see the light, i.e. Left or Right

3.  The fiber light should go into the sfp port where there is no light

Please see diagram below:  O means there is light if you are facing the Fiber & SFP port

Fiber: |OO|    SFP: |OO| ----> Correct

Fiber: |OO|    SFP: |OO| ----> Wrong

Hope this helps

[Simon Brooks]

Udld is easiest thing to use to check.


Sent from Cisco Technical Support Android App

[Andy White]

Hello,

Do I just set it globally on the remote switch first then globally on the one I'm on as it is a trunk?

I'm never really used fibre fully until now, on my CCNA and NP I only read about it

Thanks

[Simon Brooks]

Step 1	configure terminal	Enter global configuration mode.
Step 2	interface interface-id	Enter interface configuration mode, and specify the interface to be enabled for UDLD.
Step 3	udld port [aggressive]	Specify the UDLD mode of operation: •aggressive—(Optional) Enables UDLD in aggressive mode on the specified interface. UDLD is disabled by default. If you do not enter the aggressive keyword, the switch enables UDLD in normal mode. On a fiber-optic interface, this command overrides the udld enable global configuration command setting. For more information about aggressive and normal modes, see the "Modes of Operation" section.
Step 4	end	Return to privileged EXEC mode.
Step 5	show udld interface-id	Verify your entries.
Step 6	copy running-config startup-config	(Optional) Save your entries in the configuration file.