Switch ports (layer-3) terminates Laser link flaps

Unanswered Question
Jul 20th, 2008

Hi,

I have a Laser link between 2 buildings. The both ends of the link terminates on 4500 L3 switch ports.Both switches logs interface (both ends) flap atleast 3-4 times in a day, even when the Laser receival powers are good.

BGP is running acoss the link and once in 2-3 days the BGP takes few seconds hit. See below the switch port configs and suggest if you think anything need to be changed to avoid this. I do not see any major L1 errors to doubt on the cabling.

BLDGA-4510-S1#sh runn int gig 3/4

Building configuration...

Current configuration : 298 bytes

!

interface GigabitEthernet3/4

description :LOS/Laser link to BLDGB

no switchport

dampening 30 2000 200 20 restart

bandwidth 900000

ip address 10.40.2.1 255.255.255.252

logging event link-status

delay 15

keepalive 4

udld port aggressive

no cdp enable

end

*****************************

BLDGB-4510-S1#sh run int gig 4/3

Building configuration...

Current configuration : 283 bytes

!

interface GigabitEthernet4/3

description :LASER/LOS Link to BLDGA

no switchport

dampening 30 2000 200 20 restart

ip address 10.40.2.2 255.255.255.252

logging event link-status

delay 15

keepalive 4

udld port aggressive

no cdp enable

end

Thank you

MS

I have this problem too.
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lgijssel Mon, 07/21/2008 - 05:45

Hi MS,

Your interface config should be fine, the problem that you describe is unlikely to be caused by configuration issues.

A few thing came up when reading this:

1: Be aware that the laser's output level can also be too high which would be causing bit errors due to oversteered inputs. You could try to use a set of dampers to reduce the input levels.

2: Please check that the fiber cable is indeed single mode and is in accordance with the specs of the GBIC or SFP.

3: Verify that your fiber patchcables have the same specs as the fiber link.

regards,

Leo

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