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can the SFP-10G-SR down-support connect to SFP 1000BASE-SX ?

jerry zhung

Hi everybody:

today i use the SFP+ "SFP-10G-SR" in Cisco Catalyst 2960S-48TD-L connect to  1000BASE-SX SFP in 6509's module WS-X6724-SFP.

the port setting is trunk,but they don't work, even the led don't flush. then i also use the 1000BASE-SX SFP to replace SFP+ SFP-10G-SR in

2960S-48TD-L, then they cany working.

i look up the cisco data sheet , there are no data sheet to satament the 10G sfp+ can't down support 1G sfp. so i want to confirm the problem.

otherwise, the 10 SFP+ only can use for 10G SFP+ ; can't down suport 1G SFP.

this means: if  you want to use the 10G SFP+ the other old device also need to replace.

thanks~for your help!!

1 Accepted Solution

Accepted Solutions

Hi Marvin,

I found this conversation today, as I am looking for answer on question similar to question that Jerry asked, while opening this discussion.

So, my problem is the following. At some location, I need two 10GB and one 1GB connection over optical cables. To minimize costs, I tried with WS-C2960X-48FPD-L, but as it contain only two SFP+ ports, I tried with two WS-C2960X-24PD-L that will be connected with stack modules.

So, having two WS-C2960X-24PD-L, I can have 2 x 2 1GB SFP+ ports. There are two opened questions:

1. Can I put 1GB SFP transceiver module in SFP+ port (as I must have one 1GB connection to remote site)?

2. Can I use stack of two mentioned 2960 24-port switches, in a way that I use one of them for two 10GB connections (using SFP+ ports for 10GB connection), and second member of the stack in a way that one (of two available) SFP+ port is used for 1GB SFP connection (using SFP+ port as mentioned in question 1)?

I am not sure if your previous statement covers my questions, as it is not clear if 1GB SFP transceiver can be inserted in SFP+ port on WS-C2960X-24PD-L (or any other switch that has SFP+ port).

View solution in original post

37 Replies 37

Leo Laohoo
Hall of Fame
Hall of Fame

SFP+ will only support 10 Gbps.  It wil not support anything less.  This is the standard.

Dear leolaohoo:

Thanks for your help. I see the wiki and cisco 10G SFP+ datasheet as follow link. There is no mention about the 10G SFP+ which can down to  1G SFP or not and their shape are  same and also can use the fiber LC connector to link. If this is standard or protocol. Could you kindly please let me know where is the document or web link?

  Otherwise, if the 10G SFP+ only support 10Gbps, That means if  we want to replace older swiches to new 10G switches ,  we can't one by one change and need to all changes at one time. Because new switch 10G SFP+ can't down support older switch 1G SFP, or we must also plug the 1G SFP into the new switch  SFP+ module.




The 2960S-48TD-L data sheet indicates the uplink ports support either two 10Gbps SFP+ or two 1Gbps SFP modules.  So, you can install one of the following 1Gbps SFP types into the 2960S to interconnect to the 6509. 




I hope this helps.

There is no mention about the 10G SFP+ which can down to  1G SFP or not and their shape are  same and also can use the fiber LC connector to link.

And there is no mention of SFP+ able to negotiate to SFP speed either.

This page is the Cisco 10GBASE SFP+ Modules Data Sheet and you will notice the absence of any mention of 1 Gbps.  SFP+ will only run at 10 Gbps, full duplex and you can't have this go any lower.

Dear Tom and Leo:

  I highly appreciate that your help and time!!

Sincerely yours


In addition to what Tom and Leo correctly stated, the key point to remember is that there is no equivalent to software selectable speed or autonegotation in the optical domain. A given optical interface speed is fixed by the electro-optical conversion ASIC built into the transceiver hardware.