Multi Mode fibre not working

[Tabish Hussain]

Hi Team,

I have SFP-10G-SR Multimode module connected to two switch.(C9500)

The issue is when I plug multimode fibre in the module the link doesn't come up.

However, when I plug Single mode fibre in Multimode module both side of switch link come up.

Any reasons why it is happening. Why multimode fibre is not working with Multimode SFP Module?

Someone suggested because MM fibre is OM4 that is why it is not supported by older SFP modules in C9500 switches.

[M02@rt37]

Hello @Tabish Hussain,

Do you try with another MM fiber?

SFP-10G-SR support MM fiber with max reach 400m.

What is your IOS version ?

Thanks.

[Tabish Hussain]

Hi M02@rt37 

IOS version is 16.9.3.

Any fix?

[M02@rt37]

@Tabish Hussain,

Do you try with another MM fiber?

SFP-10G-SR support MM fiber with max reach 400m. That's the case for you ?

[Tabish Hussain]

Yes, I tried with different SFP module and fibre of same model but no luck.

[Mark Willis]

The SFP can't tell what fiber type is in use, all it knows is that it receives a good signal or not.

Every SFP has a range that depends on the fiber type and OM-4 generally has a longer range, so if you're within that limit you should be ok. How long is the fiber cable?

It could also be as simple as a polarity issue - reverse the tx/rx fibers on one side and see if that fixes it.

[ammahend]

For multimode check the light, make sure Rx and Tx are connected properly.

Multi-mode optical cables has wide fiber core 50 µm for OM4 (your case),  In contract – single mode optical cable core is narrow – 9 µm. When we connect multimode SFP with Single mode fiber fraction of low-intensity optical signal will get in but will fade after very short distance.

So, it is possible to connect multimode SFP with Single mode fiber, Yes– but connection will be unreliable and short.

[Tabish Hussain]

Hi @ammahend & @Mark Willis 

I just checked sfp module output and SFP-10G-SR showing media as single mode.

Please find below image. Also I cannot reverse tx rx as the both connector came fixed to each other.

[balaji.bandi]

what is the Full model of the switch - and what IOS XE code running.

as per your SR number - the product is  Product ID- SFP-10G-SR= read the product information what mode of fibre need to use :

https://www.cisco.com/c/en/us/products/collateral/interfaces-modules/transceiver-modules/data_sheet_c78-455693.html

Where is these 2 switches you trying to connect in same place or  what is the distance between these switches ?

Can you post show interface ten 1/0/8 trans

[Tabish Hussain]

Hi @balaji.bandi 

Already checked fibre to use for given SFP module. Both switch are in same room so distance not an issue.

However, we got the fix by using OM3 MM patch cord the link is coming up .

With OM4 MM patch cord it doesn't come up.

[balaji.bandi]

With OM4 MM patch cord it doesn't come up

its all depends on the cable where to buy - i have seen this issue the able shipped with OM4 and not works - so reliable vendor always good.

since all color are Aqua blue and blue color ( all are not OM4).

[Joseph W. Doherty]

Glad you found a MM patch cable that works.

BTW, Cisco notes:

Cisco SFP-10G-SR module

The Cisco 10GBASE-SR Module supports a link length of 26m on standard Fiber Distributed Data Interface (FDDI)-grade Multimode Fiber (MMF). Using 2000MHz*km MMF (OM3), up to 300m link lengths are possible. Using 4700MHz*km MMF (OM4), up to 400m link lengths are possible.

As you also tell us the two devices are in the same room, distance shouldn't be a factor, but there's many possible issues.  Which is why I was glad you found a working cable.

[Tabish Hussain]

Hi,

After earlier problem solved. I stuck in another problem, where 3 LiU's are connected from 1st floor(core sw) to 2nd and ground floor(access switch). So the port are not coming up on each side of switches connected to LiU. Using same SFP module (Cisco SFP-10G-SR) and tried with both OM3 & OM4 LC-SC multimode patch cord.

Any fix?

[balaji.bandi · Accepted solution]

First you can see on the Fibre is the Light coming ?

Do you see on SFP Light ?

make sure the Light going on SFP and Fibre should be different direction ( TX and RX lights)

All cat 9500 ? or different models ?

Try speed nonegiation - see if that fix the issue.

[Tabish Hussain]

Hi @balaji.bandi 

I went earlier today at site and changed Tx/Rx polarity which resulted in link being stored.

Thanks for revert.