I have a pair of CISCO WS-C4948-10GE's that we need to connect to a new switch that has SFP+ and QSFP ports. Is there an X2 module that supports this? If so, can someone name the part number that will work? I have found some information, but want to make sure I have the correct part number for our exact switches.

Per the discussion in the comments, I believe I have a better understanding of things now.

Would I be correct in saying that I need these SR modules on the cisco side: [url]http://www.ebay.com/itm/Cisco-original-used-X2-10GB-SR-V02-/281228948970?pt=LH_DefaultDomain_0&hash=item417a8d35ea[/url]

Then, on the switch with sfp+ ports, I can pick up an SR to SFP+ transceiver like this: [url]http://www.advantageoptics.com/SFP-10G-SR_lp.html?gclid=CKP4s-G27b4CFXQiMgodLD8AQA[/url]

and finally, an SR calbe such as this: [url]http://www.colfaxdirect.com/store/pc/viewPrd.asp?idproduct=1551[/url]

Am I on the right track here?

  • 1
    Your cisco rep would be happy to sell you the right part...give them a call? – Grant Jun 9 '14 at 15:16
  • We don't have a cisco rep. These are used switches (can't swing the prices cisco charges new). – Brian Lovett Jun 9 '14 at 15:18
  • I found these, but have no idea if they will actually work in a 4948: amazon.com/Cisco-OneX-Converter-Module-CVR-X2-SFP10G/dp/… – Brian Lovett Jun 9 '14 at 15:21
  • When you say "Is there an X2 module that supports this?" What precisely is the problem you're solving? You want a 3rd party X2 10GE optic? If so, single mode or multimode? How long is the fiber shot and is the fiber 50 micron OM3? – Mike Pennington Jun 9 '14 at 17:48
  • We have the two cisco switches mentioned in the post, and we have a third switch with sfp+ and qsfp ports. We simply need to be able to connect the CISCO WS-C4948-10GE's to the switch that has the SFP+ ports. At this point it doesn't matter how it is done, but I have to make it work. The run would only be 10 feet max at this point. (I know almost nothing about fiber and have never had to use it, so please excuse my ignorance at this point) – Brian Lovett Jun 9 '14 at 18:25

You're asking about X2 Optics, which is what the c4948-10GE uses; so the ebay picture you listed is definitely one possible option for the 4948's optics.

Whenever you build optical solutions, remember these basic issues:

  • Transceiver types must match: In this case you're using Multimode fiber SR optics. This transmit format (SR) is part of the IEEE 802.3ae standard, so just be sure that the transceiver is the same type on both sides. Vendors can be a bit picky about SFP support in their equipment, so be sure the vendor on the other side supports whichever pluggable transceiver you purchase.
  • Fiber type must match transceiver type: Buy OM3 Multimode fiber cable; the size (50 micron vs. 62.5 micron) shouldn't be a problem for the 10m distance you're considering.
  • Fiber connectors must mate with the transceiver type: You need SC connectors on one side and LC connectors on the other side.

LC Connectors:
LC Connector

SC Connectors:


If you're connecting two Cisco switches to each other, turn UDLD on the port to protect against unidirectional cabling.


If you have any problems bringing the link up, loop the transceiver to itself with a loose fiber jumper... this means technically you'd want more than just the LC-SC cable, if you don't already have fiber loopback plugs.

You can build your own MMF LC or SC loopback plug with a piece of LC-LC or SC-SC fiber. Both LC and SC connectors pull apart, and then you just take one of the strands and plug it into the TX and RX of one of the transceivers. If that transceiver lights up, then you've got a good transceiver. Conversely, if the transceiver won't loop up, you need to diagnose why (it could be something as simple as your 10GE port is administratively shutdown).

Non-Cisco optics in IOS

You've mentioned Cisco-branded parts in your question; however, in case you decide to use 3rd party optics in your Cisco, use these commands.

Switch(config)#service internal
Switch(config)#service unsupported-transceiver
Switch(config)#no errdisable detect cause gbic-invalid

Officially Cisco TAC could bark about this if they see these commands, and occasionally you find a 3rd party pluggable that doesn't work, so YMMV.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.