Best 40G QSFP+ Transceivers for Aggregation Links

40GBASE-SR4 is four 10G lanes running in parallel at 850 nm across multimode fiber. The physical consequence is the connector: an MPO-12 ferrule carrying twelve fibers, of which four transmit, four receive and four are unused. It is not a bigger version of the duplex LC pair a 10G link uses — it is a different cabling shape, and the two are not interchangeable with an adapter improvised on the day.

That leaves two honest ways to light an SR4 link. Pull an MPO trunk end to end, which is the clean answer for a new run and for anything that will later carry 100G. Or terminate the existing structured plant into MPO-to-LC cassettes at both ends, which reuses the fiber you own and adds two connection points of loss to the budget. Either is fine; discovering which one you need after the modules arrive is what costs a maintenance window.

Rated distance then varies by part rather than by standard, and every module in this list publishes its own figure. Read it against the actual run length and the fiber grade in the plant — OM3 and OM4 are not the same budget — and leave margin for the patch panels, the cassettes and the connectors the drawing does not show. Where the number lands short, the extended-reach parts on this page are the direct substitute at the same port and the same connector.

Because SR4 is four independent 10G lanes, a QSFP+ port can often be split into four 10GBASE-SR links instead of one 40G one. On a spine or aggregation switch that is a genuinely useful density trick: one port and one module serve four access-layer devices, and a chassis that looked out of 10G ports gains a whole row of them.

Two conditions have to be true, and both are on the switch rather than the optic. The platform has to support breakout on that specific port group, and the port has to be configured for it — frequently a reload, and on some platforms a restriction on which ports in a group may be split. The cable is different too: a straight MPO trunk carries one 40G link, while a breakout needs an MPO-to-4×LC harness that fans the lanes to four duplex pairs. Confirm both before the optics are ordered, because a breakout plan the switch will not honour turns four planned 10G links back into one.

The modules on this page are MSA-compliant optics built by third-party manufacturers and programmed with the identification data a given switch vendor's ports expect. That is the market this category is: the coding is what makes a module register cleanly in a Cisco, Arista, HPE, Extreme, Dell EMC or Brocade port, and it is also what makes the part non-interchangeable — the same optics under a different vendor's coding is a different order.

What they are not is an OEM part. There is no OEM warranty and no OEM support entitlement attached to a third-party module; the warranty you are buying is the module manufacturer's own, stated on the product record. Switch vendors publish their own positions on third-party optics and those positions differ, so the sensible sequence for a fleet is to confirm your support posture with the switch vendor first and standardize second. For a single lab bench or a spare kept in a drawer that conversation rarely matters; for two hundred uplinks it does.

The practical fleet advice is unglamorous. Standardize on as few part numbers as the estate allows, label the coding on the spare so nobody seats an Arista-coded module in an HPE port at two in the morning, and size the spares pool against port groups rather than against switch count.