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MPO Cable for CPAK SR10 to NCS-PP-100x10-SR


Im getting a little confused with MPO cables, polarity, gender, key up,.key down etc..

I need to connect a CPAK 100GBASE-SR10 on ASR9k to a NCS panel NCS-PP-100x10-SR basically to breakout the CPAK to 10 x 10GE SR ports via the NCS panel

From datasheets and on inspection of the ports its clear that the ports are male (with pins) therefore the patch cord needs to be female.

The confusing part is the polarity. I believe polarity A is required since a straight connection between CPAK and NCS PP is needed as the fibre patch cord from the PP to the 10G port on the router connecting to the CPAK swaps A and B ports as any standard fibre patch cord would do.

Polarity A specifies KEY UP on one side and KEY DOWN on the other if I get this right, however again inspecting the ports on CPAK and NCS panel seem to have a KEY UP on either side, implying a polarity B MPO cable not polarity A, hence the confusion.

Would be great if anyone can demystify :)



13 Replies 13

Nicolas Fevrier
Cisco Employee
Cisco Employee

Hi Mark,

I'm far from a specialist on the matter but I have on my notes that to connect two routers back to back we needed to use MPO-24F (female) key up (type B). I don't see why it should be different to connect to a patch panel ?



Hi Nicolas,

I think I'd agree that you need Type B.

The difference between your setup and mine is that you are connecting routers back to back so TX from one side must reach RX on the other, so you need a 'twist' in the cable, while I have a patch panel which is essentially an extension of the line card ports.

In my case since I will have a breakout panel from 100G CPAK to 10x10GE I believe I need a straight cable, since I then get the TX to RX twist from the regular fibre patch cord from the Patch Panel to my destination router connecting to the 9k.

So while the above suggest Polarity A, they key up/key down still confuses me!


Hi Mark,

  We have bought 100G CPAK SR10 transceivers and NCS-PP-100X10-SR, I need to buy fibers before I receive new devices and I have the same doubts than you.

  How have you solve it finally?

  MPO port in NCS-PP-100X10-SR is male o female?

  What type have have you used (A or B)?

Best Regards,


Martin Dugre
Cisco Employee
Cisco Employee

For LR, cable will be SMF, MPO-24F, female to female, Key up to Key down, crossover, APC to APC

For SR, cable will be MMF, MPO-24F, female to female, Key up to Key down, crossover, UPC to UPC

Note: it would be the same cable for router to router connection.

The crossover is from A to B, but the fibers 1-12 on each row are not crossed, i.e. A-1 to B1, etc, not A-1 to B-12. As fibers 1-12 are not crossed, the connectors would be key up to key down. See illustration:


We have two CPAK 100G SR, one in each A9K and we want to connect them directly

Supplier told us that this cable is the right one

Is this correct? I was searching a lot and i could find only Polarity A with 24 Fiber cables.

Site is on German but it says "for direct connection between CFP".


The cable you mention is for CFP/CXP, which are different transceivers than CPAK 10x10. Whether that cable conforms to the specifications above I cannot tell.

We need to connect a Cisco CPAK-10X10G-LR module with a Cisco NCS-PP-100x10-LR panel.


I know that the connector must be  MPO-24 SMF APC female on both ends, but what is the polarity we have to use?


¿is it a crossover cable like you mentioned before?


Best Regards

Hi Martin,


I originally opened this thread for link from CPAK on ASR9k to breakout patch panel for 10x10G SR

For this Im quite sure we had used Type A


Now I need to ASR9k CPAK back to back to another ASR9k CPAK, again 10x10G SR.

Can you confirm that type A (female key up to female key down) is required for both cases ?


It does not sound correct somehow, as for the router to router I need to connect TX to RX, while for the breakout I need a straight cable as the TX->RX is taken care of by the regular (ie non MPO) patch fibre from the LC connector on the breakout towards my 10G router port no ?  (as otherwise i would swap TX and RX twice over)





Which MPO-24 Cable may use for back to back ASR9K 100G connectivity through CPACK-100G-SR10


 MTP®/MPO Fiber Optic Cable, 24 Fiber, Multimode 50/125, OM4/OM3  Female-Female, Method B  ???????????

See attached image. Let me know if it doesn't answer the question. 



Thanks for you your reply.


1st ; You mentioned Rollover, is it means Type-B ?

2nd; why we are using one side with KEY up and other side with Key down ? May we use Rollover (Type-B) with key up at both ends ?


please check supplier provided  MPO-24 cable data sheet (attached) may we use it for our scenario ?

(Back to back ASR9K 100G connectivity through CPACK-100G-SR10)

MPO-24 datasheet.JPG




Th nomenclature is different, but essentially it's important that:


fibre #1: connects MPO01 to MPO13

fibre #2: connects MPO02 to MPO14


fibre #11: connects MPO11 to MPO23

fibre #12: connects MPO12 to MPO24

fibre #13: connects MPO13 to MPO01

fibre #14: connects MPO14 to MPO02


fibre #23: connects MPO23 to MPO11

fibre #24: connects MPO24 to MPO12





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