[c-nsp] Catalyst 3750-X with SFP-10G-ZR transceiver - troubleshooting‏

Phil Mayers p.mayers at imperial.ac.uk
Mon Oct 14 05:25:20 EDT 2013

On 10/14/2013 07:53 AM, Joe Crap wrote:

> light instantly. I realise these two sets of transceivers are operating
>   at different frequencies (1310nm vs 1550nm) but afaik an OS1 cable
> should be fine with both, right? We've also swapped the ZR transceivers

Yes, OS1 should work fine at 1550.

>   into the same ports the LRs are working fine in, it makes no
> difference.

Is there any chance you've blown the RX input on one or both xcvr? ZRs 
typically can't tolerate bright light on RX, and if someone ever 
connected them without an attenuator...

As a general operational thing, I prefer fixed LC simplex attenuators to 
attenuated patch leads, because you can then leave the attenuator 
"attached" to the ZR RX input, and avoid any forgetfulness about the 
nature of what you're doing. Attenuated patch leads OTOH are too easy to 
forget about.

> I'm afraid my own fiber knowledge is quite limited (much of it learned
> from trying to troubleshoot this!), but can anyone suggest further
> troubleshooting steps? We don't have the equipment to run an OTDR test
> on the patch leads, and I'm trusting the DOM reporting to be at least
> vaguely accurate for signal strength.

Couple of things:

If you don't have a handheld lightmeter, consider getting on in the 
future - they're useful. If you do, use it! Sadly that'll only verify 
TX, which is unlikely to be where the problem lies.

The other thing you can try is substituting an LR for ZR at one end; the 
receivers in the xcvr are normally wideband and in theory a 1310 and 
1550 optic can link-up (although the last time I tried this, I think it 
failed). Obviously you'll need attenuate asymmetrically for this to work 
- the ZR will likely overdrive the LR RX, and vice-versa, but by 
different values (~3 and ~7dB, respectively). Again simplex attenuators 
win here!

Of course it's also possible that Cisco have messed up in IOS; do you 
have another device (another vendor?) you can put the xcvr in to test?

If it's an xcvr fault, and only one is dead, you might be able to 
determine which one by disabling autoneg - if one end comes up and the 
other doesn't, the link-down end has dead RX (or far-end dead TX).

Good luck!

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