Clarification on SFP+ and SFP28 compatibility

Zarathustra[H]

Extremely [H]
Joined
Oct 29, 2000
Messages
35,405
Hey everyone,

The more I google on this, the more it muddies the waters. Some sources say SFP+ and SFP28 are compatible, others say they aren't, so I figured I'd seek clarification here from someone with actual experience with them.

1.) If I have a SFP+ port with an SFP+ 10GBase-SR transducer on one end of an fiber with an LC-LC connector, and an SFP28 port with an SFP28 and a 25GBase-SR transducer on the other end of that fiber, will they generally autonegotiate the slower 10Gig speed and work?

2.) Can I stick a 10GBase-SR SFP+ transducer into an SFP28 port and have it function, just at the lower 10gig speed?

3.) Can I stick a 25GBase-SR SFP28 transducer into an SFP+ port and have it function, just at the lower speed?

Appreciate any input!
 

Nicklebon

Gawd
Joined
May 22, 2006
Messages
877
1. Generally no. In my experience there is no such thing as optical auto-negotiation. Perhaps some modules support this. As a rule matching modules on each end.
2. Yes, the socket is backwards compatible.
3. Generally yes but the module itself must support this.
 

Zarathustra[H]

Extremely [H]
Joined
Oct 29, 2000
Messages
35,405
1. Generally no. In my experience there is no such thing as optical auto-negotiation. Perhaps some modules support this. As a rule matching modules on each end.
2. Yes, the socket is backwards compatible.
3. Generally yes but the module itself must support this.

Thank you for that. I can see now why the information out there can seem conflicting.

So Port 1 on both sides would look like this:

First 25gbe NIC --> 10GBase-SR SFP+ Transducer --> 10GBase-SR SFP+ transducer --> 10G Switch --> 10GBase-SR SFP+ transducer --> 10GBase-SR SFP+ transducer --> Second 25gbe NIC

Port 2 on the other hand (on a different subnet) would look like this:

First 25gbe NIC --> 25GBase-SR SFP28 Transducer --> 25GBase-SR SFP28 Transducer --> Second 25gbe NIC


(In my setup the second port/subnet is dedicated to storage traffic so I don't overload and slow other things down)

Do you know if 10G SFP+ DAC cables generally work in 25gbe SFP28 adapters? It sounds like they probably should if they are compatible with SFP+ but there will always be compatibility issues with these things. Intel NIC's tend to be pretty friendly when it comes to which DAC cables and transducers they will work with though. At least that has been my experience.
 

Balkroth

Limp Gawd
Joined
Dec 15, 2011
Messages
441
Thank you for that. I can see now why the information out there can seem conflicting.

So Port 1 on both sides would look like this:

First 25gbe NIC --> 10GBase-SR SFP+ Transducer --> 10GBase-SR SFP+ transducer --> 10G Switch --> 10GBase-SR SFP+ transducer --> 10GBase-SR SFP+ transducer --> Second 25gbe NIC

Port 2 on the other hand (on a different subnet) would look like this:

First 25gbe NIC --> 25GBase-SR SFP28 Transducer --> 25GBase-SR SFP28 Transducer --> Second 25gbe NIC


(In my setup the second port/subnet is dedicated to storage traffic so I don't overload and slow other things down)

Do you know if 10G SFP+ DAC cables generally work in 25gbe SFP28 adapters? It sounds like they probably should if they are compatible with SFP+ but there will always be compatibility issues with these things. Intel NIC's tend to be pretty friendly when it comes to which DAC cables and transducers they will work with though. At least that has been my experience.
I haven't had a problem with 10G DACs working in SFP28 Ports, general compatibility with those things aside. In intel XVV710 Adapters I've not seen any general issues (I just always order Cisco compatible DACs, even third party ones with their firmware flashed properly seem fine).
 
Top