Catalyst 3750X 10 Gig Optical Cable Issues

[James Hawkins]

Hi,

I have just installed a new 10 Gbps core for a small customer comprising two Catalyst 3850-24XS switches that are stacked together to form one logical switch. The 3850 stack is running software version 03.07.03E

The old core which comprised two Catalyst 3750X-48T-S and one C3750G-48TS switches stacked is now a server farm switch. Each 3750X has a C3KX-NM-10G module installed. This can support either four 1GB SFPs or two 10GB SFP+ slots. The 3750 stack is running software version 15.0(2)SE5 as this is the latest software version that the C3750G-48TS can support.

The customer also uses Catalyst 2960S-24PD-L access switches running software version 15.0(2)SE8.

To link the switches together I used SFP-10G-AOC2M= 10GBASE Active Optical SFP+ Cable 2 Meter cables. These did not work when connecting the Catalyst 3850 to the Catalyst 3750 switches but work fine when connecting the Catalyst 3850 switches to the 2960S switches.

I had some longer cables - SFP-10G-AOC7M= 10GBASE Active Optical SFP+ Cable, 7 Meter - and these work fine between the Catalyst 3850 and 3750X switches.

Has anyone else seen this and, if so, can you offer an explanation. The longer cables were bought to connect new servers at 10 Gbps and so can only be a temporary fix.

I guess I could get the customer to buy more 7 meter cables but it is a bit silly as the 3850 and 3750 are in the same rack and so lots of cable would be wasted.

Thanks for reading

James

[Reza Sharifi]

Hi James,

That is very strange. The length of that cable should not matter as long as the optic is compatible.

Since the switches are in the same rack, 2 meter cable does not work and you may end up with too much cable hanging, you may want to try 3 meter. Just a suggestion since the price is almost the same, but than again you may see the same issue with 3 meter.

http://www.fs.com/products/30889.html

HTH

[James Hawkins]

Thanks for the responses guys. If have tried the test mentioned by Leo and it does seem that the 3750X is the problem device.

There is a later version of software - 15.0.2-SE9 - which is supported on both types of 3750 switch in the stack that I can try using.

I will also look at getting some alternate cables from fs.com - thanks guys!

[Leo Laohoo]

James, 

I'm suspecting you're seeing an IOS bug.  The problem is which one of the two has the IOS bug.  

Connect the 2m cable (both ends) to the 3750X and see if the link goes up or not.  Do the same to the 3850.  

If the link doesn't go up on the 3750X then this is where the IOS bug is and this could pose problem because 3750X is considered as "old" (if you know what I'm saying, *blink*, *blink*, *blink*).