About 4x10G SFP+ <--> QSFP breakout cable

Question

I have my very first Nexus switch to install in our new datacenter. It's a 3172TQ that comes with 4 QSFP+ ports.

All my other devices have SFP+ modules. I did a little research and i found about the QSFP-SFP+ breakout cable.

My question is: Can I plug those four SFP+ cables to different devices or do I need to connect all of them to only one? What are my options here?

One QSFP can be connected to the same single port on the client end if got it right. — B.J.Goodman, Mar 08 '18 at 16:28

score 2 · Answer 1 · answered Mar 08 '18 at 17:52

Weirdly we've been dealing with these in the last few weeks, they can be tricky buggers. In particular we've been using them from C220 M5's into 5672UP's.

Anyway theoretically you can connect 2, and only 2, of these to one Nexus and the other 2, and again only 2, to another linked Nexus and create a Virtual Port Channel for them but in practice we've had to connect all four to one switch with the second MLOM port going to the second Nexus - that works, so long as you use ALL FOUR ports, fewer aren't supported and port channel them together - oh and you can't use LACP at all.

I'm glad that this is a stop-gap solution as they'll be converted to using regular 40Gbps QSFP cables once the 5696Q switches arrive.

That's trash I never had those issues with force10. – Jacob Evans Mar 08 '18 at 22:21 — Jacob Evans, Mar 08 '18 at 22:21

score 1 · Answer 2 · answered Mar 08 '18 at 16:49

You can use either mode:

The Cisco Nexus 3172PQ (Figure 1) is a 10-Gbps Enhanced Small Form-Factor Pluggable (SFP+)–based ToR switch with 48 SFP+ ports and 6 Quad SFP+ (QSFP+) ports. Each SFP+ port can operate in 100-Mbps, 1‑Gbps, or 10-Gbps mode, and each QSFP+ port can operate in native 40-Gbps or 4 x 10-Gbps mode. This switch is a true phy-less switch that is optimized for low latency and low power consumption.

Source Cisco

You will not have access to those ports until AFTER you plug in your 'supported' breakout cable.

The breakout ports are in administratively enabled state after the breakout of the ports into 4x10G mode or the breakin of the ports into 40G mode. On upgrade from the earlier releases, the configuration restored takes care of restoring the appropriate administrative state of the ports.

score 0 · Answer 3 · edited Jun 11 '20 at 10:02

You need to make sure you break out at the Nexus side - otherwise it treats the QSFP+ port as a single 40G connection. Once that is done, each single 10G SFP+ end of the breakout can go to a different switch.

Check the Nexus 3000/9000 Consolidated Interface Breakout configuration:

Nexus 3172

The 3172 has a single hardware profile, 48X10G+breakout6x40g. The 40GB ports can be broken out individually with the "speed 10000" command.
They can be collapsed with the "speed 40000" command.

About 4x10G SFP+ <--> QSFP breakout cable

3 Answers3

Linked