10GB SFP or 1GB SFP for a 10GB switch connecting to a 1Gb Switch

[hoosier2933]

Hello, I have two Catalyst 2960x's on each end of newly run 10GB fiber. One switch only has 1Gbps spf slots, and the other has 10Gpbs spf slots. Im obviously going to have to put 1Gbps sfp module in the 1Gbps switch, however I was wondering if I should buy the 1Gbps sfp module or the 10Gbps sfp module for the 10Gbps switch on the other end. It would make sense to buy the 10Gbps module for future upgrades on the other end, but I didnt know of the 10Gbps module would work connected to the 1Gbps module on the other end. Would they just auto negotiate and the 10Gbps end would run down at 1Gbps? Thanks in advance for the help.

[Reza Sharifi]

Hi,

You need to have the same type of connection speed on both side. So, if you want to do 10Gig, you need it on both side and the same for 1Gig. Do not try 10Gig on one side and 1Gig on the other side, as it will NOT work. Also, It makes sense to upgrade to 10Gig but before you do that, make sure that you switch model actually does support 10Gig.

HTH

[hoosier2933]

Thank you for your reply. So on one end i have a Catalyst 2960x that does have 2x 10Gbps sfp slots. The swtich on the other end is a Catalyst 2960x that have 4x 1Gbps sfp slots. So on the 1Gbps switch side, i know i need to use a 1Gbps sfp module, GLC-SX-MMD. So i know this connection is only going to be 1Gbps, however I was wondering if on the other end, the 10Gpbs switch end, can I used a 10Gbps sfp module like a SFP-10G-SR. Will that SFP-10G-SR be able to notice the other end of this connection is a 1Gbps sfp module, and then autonegotiate down to that 1Gbps speed? Or, do i need to use a 1Gpbs sfp module on both ends, so put a GLC-SX-MMD on both ends of this connection to get it to work? The 10Gbps swtich does support the GLC-SX-MMD 1Gbps module, i just didnt know if i had to use 1Gbps module on both ends to get it working. Thanks

[marce1000]

  >...Will that SFP-10G-SR be able to notice the other end of this connection is a 1Gbps sfp module, and then autonegotiate down to that 1Gbps speed?
                  It won't , speed must always match ,  (for fiber)

 M.

[Reza Sharifi]

 I was wondering if on the other end, the 10Gpbs switch end, can I used a 10Gbps sfp module like a SFP-10G-SR. Will that SFP-10G-SR be able to notice the other end of this connection is a 1Gbps sfp module, and then autonegotiate down to that 1Gbps speed?

No, this will not work, as the speed and duplex on fiber ports can not be negotiated up or down. So, as long as the 10Gig side support 1Gig SFP ( GLC-SX-MMD) you can simply insert 1Gig SFP and you are good. Again, make sure that the 10Gig side actually can support 1Gig SFP, as depending on the switch/module, some 10Gig ports only support 10Gig SFP+ and not 1Gig SFP.

Can you provide the exact model for both switches?

HTH

[hoosier2933]

Understood, again I appreciate the help. I did lookup both models in the sfp compatibility matrix, but if you'd like to confirm that would be great. On one end I have the 2960X-48LPD-L, and other end 2960X-48LPS-L.

[Reza Sharifi]

Ok, let's look at table-27 (#2 and 7) in this link. 

It appears that 2960X-48LPD-L supports 2 10Gig SFP+ only and 2960X-48LPS-L supports 4 1Gig SFPs only. So, you may not be able to connect these switches via fiber. 

https://www.cisco.com/c/en/us/products/collateral/switches/catalyst-2960-x-series-switches/datasheet_c78-728232.html

HTH

[hoosier2933]

Gotcha, i was looking at the sfp compatibility matrix and it appeared that the 10Gig switch does support the same 1Gig sfp module as the 1gig switch. GLC-SX-MMD

https://tmgmatrix.cisco.com/?npid=654&npid=658

[Reza Sharifi · Accepted solution]

Unfortunately, the compatibly matrix is not always correct. Usually, the uplinks for LAN Base switches are fixed, meaning they are 1 or 10 and not both. That said, to be sure, and for testing, you may want to try a  GLC-SX-MMD in one of the 10Gig ports and hope you see the link comes up.

HTH

[hoosier2933]

Thanks, bottom line it sounds like a speed mismatch on either end of fiber is a roll of the dice. I will give the 1gig module a try in the 10gig port and see if i have any luck. I can always use a fiber to ethernet media converter for now i guess on both ends and bypass the sfp slots all together. 

[Reza Sharifi]

 I can always use a fiber to ethernet media converter for now i guess on both ends and bypass the sfp slots all together. 

That is correct. If you decide that you want to use one of the copper ports, you can for example do this:

port 1/0/1----MC----fiber------------------fiber----MC-----port 1/0/1

If your fiber is Multimode with LC type connectors, you need a 1Gig MC LC/copper on both sides. If your fiber is single-mode the SFP on the media converter needs to be single-mode as well.

Good Luck! 

[hoosier2933]

Wanted to follow up and confirm the 1gig sfp module GLC-SX-MMD did work in the 10gig slp slot on the 2960X-48LPD-L. So GLC-SX-MMD sfp modules on both ends did bring up a 1gig link for me. Thanks.

[Reza Sharifi]

Nice. Thank you for the feedback!