I am new to infiniband networks, but i need to extend an existing infiniband cluster with some nodes. During my exploratory web-research I came across some to me ambiguous descriptions of cables, connectors and switches.

According to Wikipedia QSFP is specified as 4x1Gb/s, and QSFP+ as 4x10 or 40 Gb/s. However many suppliers on the web are offering QSFP cables and switches for 40 Gb/s. This some how does not seem to match with the overviews on different infiniband cabling that i found.

Is this just sloppy naming and are these QSFP 40Gb/s actually QSFP+? Is there a difference in the physical connections between QSFP and QSFP+? Or are just the cables of a different quality (like CAT6 and CAT7 cables), but is the shape of the connectors the same?

I would be very thankful if some body could clarify this a bit.

  • 2
    You're talking about ethernet QSFP/QSFP+'s - Infiniband uses its own QSFP's such as QSFP28's etc. You need to use the optics that are supported by the HBAs.
    – Chopper3
    Apr 3, 2017 at 9:47
  • 1
    Yes QSFP+ has several variants 4x10, 4x14, and 4 x 28 Gbit/s. My question is about how QSFP 40Gbit/s is related to QSFP+ 4x10. Are they refering to the same, or is QSFP 40Gbit/s a commonly used but non-standard specification. Indeed my aim is usually to use supported or compatible optics, and switches.
    – Hjan
    Apr 5, 2017 at 7:22
  • 40Gb and 4x10Gb are obviously incompatible - the latter uses CWDM to carry four lambdas whereas the 40Gb native ones carry a single signal.
    – Chopper3
    Apr 5, 2017 at 7:53
  • Unfortunately, QSFP+ cables (and furthermore the addition of 4x14 cables in addition to the 4x10 cables) are usually referred to by a colloquialism of QSFP cables. More commonly, cables used for InfiniBand use are referred to by the data rates they run. E.g. QDR cable or FDR cable. Since you can often run FDR equipment at FDR rates with FDR cables, you'll just need to know if the vendor certifies the cable in question for the rate you need before buying it. If a vendor doesn't know, it's probably not going to work for the rate you need.
    – Paul
    Nov 15, 2017 at 21:41

2 Answers 2


QSFP+ stands for Quad (4-channel) Small Form-Factor Pluggable Plus, also known as QSFP10. Now QSFP/QSFP+/QSFP28 all use 4 channels to pass data.

QSFP - People mistake this for QSFP+ ALL the time. Make sure you read the full description. QSFP is a 4x4Gbps (16GB) transceiver/cable. These are outdated and not really used from what I have seen

QSFP+ these are 40G or 4x10Gbps as each channel has 10GB speeds. These can be a single cable, QSFP+ to QSFP+ or QSFP+ breakout to 4xSFP+

QSFP28 are 100G cables, can also be 4x25G or 2x50G breakout cables.

  • 1
    Thanks. Do you happen to know if the physical connections between QSFP and QSFP+ are the same/identical. Is it physically possible to mistakenly connect a QSFP cable in to a QSFP+ port? Or are the connectors sufficiently different, to avoid such a mistake?
    – Hjan
    Aug 24, 2017 at 9:27
  • 2
    Unfortunately, All QSFP/QSFP+/QSFP28 that I have seen all look identical and have the same connector. On the label that comes with the cable it should have the data rate listed as a part# or description. You can also plug them into the switch or system and view the inventory or transceiver information and it will tell you.
    – KrisGT
    Aug 24, 2017 at 18:36
  • They have the same connectors because they are compatible - you can plug a QSFP+ into a QSFP28 "port" and it will run with QSFP+ speeds ;) This makes it hard to distinguish them, but is convenient for a lot of things.
    – TomTom
    Apr 13, 2018 at 8:55

Additionally, QSFP modules are commonly available in several different types: 4x1G QSFP, 4x10G QSFP+, 4x28G QSFP28. From this side, QSFP/QSFP+/QSFP28 all share the same small form-factor. Literally QSFP uses 4x1G lanes and was only found in some FC/IB contexts.

QSFP+ was evolved from 4x1G lanes (QSFP) to 4x10G lanes, which is designed to support 40G Ethernet, Serial Attached SCSI, QDR (40G) and FDR (56G) Infiniband, and other communications standards. So QSFP+ can break out into 4x10G or 1x40G connection.

(source: http://www.fiber-optic-equipment.com/difference-between-qsfp-qsfp-qsfp28.html)

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