Fibre link down down on both ends

mahesh18 · ‎11-06-2012

Hi everyone,

We have Fibre link down down from both ends.

From switch A goes to fibre box then to other fibre box then to switch B.

Switch A

Model: WS-X4418-GB-Gbic

Type: 1000BaseSX

Switch B

Model: WS-C3750G-24TS-1U

Type: 1000BaseSX SFP

Both sides are configured as trunk

Thanks

Mahesh

acampbell · ‎11-06-2012

Mahesh,

You need to make sure that the fibre link is using multimode fibre

for these gbics.

Also

SWITCH A -------- TX ------------> RX ------> SWITCH B

SWITCH A <------ RX <------------ TX ------- SWITCH B

Regards,
Alex.
Please rate useful posts.

Regards, Alex. Please rate useful posts.

mahesh18 · ‎11-06-2012

Hi Alex,

Can you please tell what prompted you to say that use multimode fibre?

how you figure this out?

Thanks

MAhesh

acampbell · ‎11-06-2012

Mahesh

Your gbics have the "SX" key

This means short haul uses MultiMode Fibre

There are many links on CCO to look at

Here is just an example

http://www.cisco.com/en/US/prod/collateral/modules/ps5455/ps6577/product_data_sheet09186a008014cb5e_ps872_Products_Data_Sheet.html

TABLE 1

Table 1. Cisco GBIC Port Cabling Specifications

GBIC

Wavelength (nm)

Fiber Type

Core Size (Micron)

Modal Bandwidth (MHz/km)***

Cable Distance

Cisco 1000BASE-SX

850

MMF

62.5

50.0

160

200

400

500

2000

722 ft (220 m)

902 ft (275 m)

1640 ft (500 m)

1804 ft (550 m)

3281 ft (1000 m)

Regards,
Alex.
Please rate useful posts.

Regards, Alex. Please rate useful posts.

darren.g · ‎11-06-2012

mahesh18 wrote:

Hi everyone,

We have Fibre link down down from both ends.

From switch A goes to fibre box then to other fibre box then to switch B.

Switch A

Model: WS-X4418-GB-Gbic

Type: 1000BaseSX

Switch B

Model: WS-C3750G-24TS-1U

Type: 1000BaseSX SFP

Both sides are configured as trunk

Thanks

Mahesh

On the 3750, do you have the following command

speed nonegotiate

on the fibre port (ge1/1/1, or whichever port you have your SFP in)?

The 3750 won't connect an SFP fibre link without this keyword.

Cheers.

mahesh18 · ‎11-06-2012

Hi Darren

I checke dthe config of port on 3750 which has fibre link and is up up.

It has no speed nonegotiate command.

i checked int status

a-full a-1000 1000BaseSX SFP

This shows that it is auto negotiating

Thanks

MAhesh

Reza Sharifi · ‎11-06-2012

Hi Mahesh,

Since your Gbic and SFP are both SX, you need multimode fiber. SX is for short reach and LX is for long reach fiber.

Usually, but not always if the color of the fiber is aqua or orange the fiber is multimode and if the color is yellow usually that is single mode.

Gbic use SC type connector on the tip of the fiber and SFP use LC type of connector. If the link is not coming up at all (down down) try crossing the fiber tips on one side. Usually for SC one strand is blue and the other is red. switch them around and test again.

HTH

Reza

mahesh18 · ‎11-07-2012

Hi Reza,

You provided very useful information.

As link is down down right now and we have another working link between 2 switches so we are ok for now.

The first thing that i will test is by crossing the fibre tips on one side.

However i can only do this after few days when we have change window.

Many thanks

Mahesh

darren.g · ‎11-06-2012

Mahesh.

I'm a little confused - your original post says your link is down down at both ends - now you're saying the 3750 is up up?

Can you clarify the interface status from both switches with the "shwo int x/x/x" commands and post the results?

The only way for the 3750 to have that interface in up/up status is if it's got a valid, working link to the other end - the line protocol won't come up unless it's got a link.

Actually, I can think of one situation where it might come up but still not work - you have receive (light) inbound, but your outbound to the other end is broken or not working.

Have you confirmed that both fibres are actually functional (swap the transmit/receive and see if you have light coming out both ends on each fibre in the pair - do *not* look directly into it). Since you're using SX transceivers, you should be able to see red light from one fibre at eache end if you have a tranceiver plugged in.

One thing nobody has asked - how long is the fibre run between the switches? Depending on the fibre type, SX tranceivers may only be good for as little as 200 metres cable distance.

Cheers.

mahesh18 · ‎11-06-2012

Hi Darren

in earlier post i mean to say that i checked config of other fibre link which is working fine.

sorry to confuse you.

For fibre link not working distance is less than 100 feet.

Regarding posting the int status i can post tomorrow as currently i have no access to ports.

Also regarding testing mostly i will do tomorrow after hours and keep you posted.

Thanks for help.

Mahesh