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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


oh forget that, this is GL for OEM avago , Partnumber is AFBR-703SDZ-GL. 10G SR.




I'm running into something similar.

We just put in new 4451 routers with GLC-SX-MM Part # 30-1301-03 (SFP's)

and we're trying to connect to a new 4507R+E 10gig Module using SFP-10G-SR Part#10-2415-03.

When we plug in the new cable we get no link light on the 4507 and are unable to ping between the two devices.  I've been told you can't connect a 1Gig SFP to a 10Gig SFP, so we're trying to decipher the truth of this matter as we'd prefer fiber vs. copper.

Thanks for any suggestions!

As noted elsewhere in this thread, a Cisco SFP-10G-SR only runs at 10 Gbps.

It will never establish a link with a downstream Cisco GLC-SX-MM which only runs at 1 Gbps.

Thanks Marvin!

Now that we've established that, we'll just have to stick to the copper.

Marvin has answered your query.  You're in good hands.  :)



If i am not wrong, Sfp 10g sr must be running at single mode and GLC sx-mm must be a multimode sfp. 

I don't think they both will negotiate to make the link up.



The SFP-10G-SR operates via multimode, as does the GLC-SX-MM. It's not the coherent laser (singlemode fiber or SMF) vs. incoherent VCSEL or LED (multimode fiber MMF) light - it's the frequency that doesn' t match.

For anybody who's interested, have a look at this reference on SMF vs. MMF.

Thanks Marvin.

The SFP-10G-SR operates via multimode, If I connect the SingleMode fiber, Would it be functioning? 

No.  Wrong laser type.  

Use a SFP that is compatible with singlemode fiber (SMF), per the attached data sheet:

according Q&A the Cisco catalyst 2960 -X and -S, the SFP+ can support both speed 10Gbps and 1Gbps but not lower

Q.    Can the 10 Gigabit SFP+ slots on the Cisco Catalyst 2960-X model support 1 Gigabit SFP modules?

A.     Yes. The Cisco Catalyst 2960-S models that support 10 Gigabit SFP+ modules can also support SFP modules that operates at 1 Gigabit.
Q.    Can the 10 Gigabit SFP+ slots on the Cisco Catalyst 2960-X models support 100-Mb SFP modules?
A.     No. The Cisco Catalyst 2960-X models that support 10 Gigabit SFP+ modules cannot support SFP modules that operate at less than 1 Gigabit.

An SFP+ slot is compatible with an SFP transceiver. In that case it is acting effectively as an SFP slot.  Kind of like an old blade in a 6509 only using half of the backplane fabric.

That's different than the case of an SFP+ 10 Gbps transceiver operating at 1 Gbps. That's what will not work.

Is it possible to connect a 3850 Switch with a Cisco SFP-10G-SR to another switch with a 1000BASE-SX module.? kindly advise

Induraj - you can connect them but you won't get a link. So, no this is not a practical approach. Both switches need to have SFPs operating at the same speed.


Thank you very much !

Sorry to ask again "you won't get a link" - This mean link wont come up right  ? kindly clarify



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