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New Member

do I need cross over for fiber?

Hi everyone,

Thank you for your help in advance.

I am troubleshooting a fiber connectivity issue.Now I have two switches, one is 3750, and another is small biz 300 series switch. Both switch has a single mode smf gbic. Now I have two swtiches face to face and connect with a single mode cable. Do you think if I would get a link light on? Both ports are no shutdown.

The reason I said this is that...after a long story, I suspect one of the gbic is bad. Any otherway to tell if my gbic is good or bad too?
Thank you very much.

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Accepted Solutions
New Member

do I need cross over for fiber?

I know theres a way to get GBIC statistical and operational information. Ive done this on a 6500 seriess before and it was very beneficial. Im not sure of a direct way to determine if you have a bad GBIC or not simply by looking at it. I was able to issue the commands below while in Priveleged Exec mode. Not to sure if this will even work on the 3750 but depending on the IOS its always worth a shot

show inventory

show inventory raw

But check this Link out

https://supportforums.cisco.com/docs/DOC-5463

FYI not sure if you want to test with some non cisco branded GBICs but these commands will allow you to do so to determine the operational status of the port/interface

service unsupported-transceiver

no errdisable detect cause gbic-invalid

errdisable recovery cause gbic-invalid

do I need cross over for fiber?

You need not to cross.

check that picture and you see how your cable has to look like.

http://commons.wikimedia.org/wiki/File:SFP-front-RX-TX.jpg

Or cisco doc.

http://www.cisco.com/en/US/products/hw/modules/ps4999/products_tech_note09186a00807a30d6.shtml#model3

regards,

Sebastian

pls. rate if helpful

3 REPLIES
New Member

do I need cross over for fiber?

I know theres a way to get GBIC statistical and operational information. Ive done this on a 6500 seriess before and it was very beneficial. Im not sure of a direct way to determine if you have a bad GBIC or not simply by looking at it. I was able to issue the commands below while in Priveleged Exec mode. Not to sure if this will even work on the 3750 but depending on the IOS its always worth a shot

show inventory

show inventory raw

But check this Link out

https://supportforums.cisco.com/docs/DOC-5463

FYI not sure if you want to test with some non cisco branded GBICs but these commands will allow you to do so to determine the operational status of the port/interface

service unsupported-transceiver

no errdisable detect cause gbic-invalid

errdisable recovery cause gbic-invalid

do I need cross over for fiber?

You need not to cross.

check that picture and you see how your cable has to look like.

http://commons.wikimedia.org/wiki/File:SFP-front-RX-TX.jpg

Or cisco doc.

http://www.cisco.com/en/US/products/hw/modules/ps4999/products_tech_note09186a00807a30d6.shtml#model3

regards,

Sebastian

pls. rate if helpful

New Member

do I need cross over for fiber?

hi,

i actually dont agree with sebastian.

you need to cross one side of the fiber cable as otherwise the transceiving side would connect to the transceiving side and the receiving side would connect to the receiving side. and then you wouldnt get a connect.

one side of the cable must be crossed so its rx on tx.

some cables come already with a little attachment on one side, crossing them by default, but if you cable doesnt have this attachment you have to cross it manually.

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