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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!!

37 Replies 37

Link will not come up. No. Matter. What. :)

I didn't want to say you cannot connect them since they will each physically take an LC connector. However doing so will not result in a working link.

Not entirely true.  On Nexus I'm using the 10G twinax running at 1G.  I used the "service unsupported-transceiver" command on the interface and it came right up.  So far no issues.  I know this isnt fiber so it may not apply.  

As far as I know these can only do 10 gbps ( and can't fall back to 1 gbps )

Kind regards.

If this is a Nexus switch; and one is only going to run 1gb on this
port; why wouldn't one put a 1g SFP in that particular port and save the
10g ones for ports that actually are going to be connected at 10g? The
switch itself should be able to handle both SFP's. And the connection
is point-to-point.

We have both nexus 9k's and nexus 5k's; and the 9k's auto sense the SFP
(and thus the speed) in a particular port. The 5k's seem a bit more
primitive; you have to tell it the port speed it should use.

In my case this was a quick fix because no RJ45 1G SFP's were on hand but there were excess twinax cables available.  We are ordering those now.  Other than support issues, if they work I dont see why we shouldnt use them.

That would make sense if you can obtain twinax cables of reasonable
length. I just figured if you had one 1g SFP, you probably had more.

On another note; which many folks may not know; Prolabs makes a "Cisco
compatible" 10g RJ45 copper SFP that works well in Nexus switches. I
have several in use in my lab. They also tend to work well in various
(originally fiber) ethernet cards that have removable SFP ports. As far
as I know, no one else makes 10g RJ45 SFP's. Took me a while to find
them. Not sure why more vendors - including Cisco itself - doesn't make
them; since I'm sure that many places have legacy copper (RJ45) patch
panels and trunk runs; and if they're cat6 they're probably just as
reliable (and simpler to use since you don't have to run any extra long
cables) than twinax.


We have Cisco core and edge switches with SFP-10G-SR-S connected with an OM3 fiber backbone. We are experiencing an issue that the link will run only if an OM3 patch cord is used to patch the sfp to the backbone fiber panel. The link won't come up if we patch it with an OM2 patch cord. Is there any technical reason for this failure?

You don't need to look only to the length of the OM2 patch cable, but to the entire link length.

OM2 has bandwidth 500. Max distance in 10 gbps is 82 m

OM3 has bandwidth 1500. Max distance in 10 gbps is 300 m

So your relatively short OM2 patch cord kills the link ( not enough fiber budget left over to reach the end of the entire link ) ...

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