40GbE - The Older Generation, Often the Cheapest Switched Tier

40GbE (QSFP+) network cards in stock now

QSFP+ direct-attach cables (including 40G-to-4x10G breakout)

Passive direct-attach copper, by length. A DAC is a fixed-length cable with the transceivers moulded on - you buy the whole run at once rather than a cable plus two modules.

QSFP+ transceivers

Every "compatible with" phrase below is the seller's own wording, recorded as a claim and badged. We have not tested any module against any switch.

QSFP+ optics availability, stated as documented

QSFP+ transceivers exist for this tier - our table above tracks 40GBASE-SR4 multimode modules - but the selection is narrower than the SFP28 tier above it, reflecting a smaller, older, more specialised market rather than anything about the standard itself.

40GBASE-SR4 uses an MPO/MTP multi-fibre connector rather than the duplex LC connector the 10G and 25G optics in this cluster use - a physically different fibre patch lead, not just a different transceiver. Check that your fibre plant (or patch cable purchase) matches MPO/MTP before assuming an existing LC run works with a 40G optic.

As everywhere else in this cluster, a passive QSFP+ DAC sidesteps the whole optics question for a short run, and is the cheaper, cooler default recommendation for two machines near each other.

Breakout behaviour, per the standard

A QSFP+ 40G port is four 10G lanes bundled into one connector, and a breakout DAC splits them into four independent SFP+ legs - the same relationship a 100G QSFP28 port has with four 25G legs, one tier up. Live 40G-to-4x10G breakout listings are in the DAC table above and in the cabling guide.

Whether a specific switch or card actually supports breaking out a given port is a per-model, vendor-documented fact rather than something guaranteed by the connector alone - check the switch's own documentation before buying a breakout cable expecting it to work on every port.

Where to go next

The 25/40/100GbE hub has the full cluster and the form-factor map · 100GbE is the tier above this one, where breakout cabling usually is the point · ConnectX-4 is the card this page's live builds use · the cabling guide covers every DAC, AOC and optic across all three tiers · rack disk shelves are common hardware behind a build like this.

Frequently asked questions

Sources

Specification claims on this page were checked against the pages below on 4 August 2026. Where a widely-repeated figure did not survive that check, we report what the source says now and say so in the text rather than repeating the familiar number.

1. NVIDIA (Mellanox) - ConnectX-3 EN product line and lifecycle status (nvidia.com, 2026)
   Used for: that ConnectX-3 has reached end-of-life status with NVIDIA, and the MCX311A / MCX312A / MCX314A part-number family. EOL means no new firmware or driver work from the maker; it does not mean the card stops working, and the page says so in those terms.
2. The Linux kernel project - mlx4, mlx5, ixgbe and i40e in-tree Ethernet drivers (kernel.org, 2026)
   Used for: that mlx4 (ConnectX-3), mlx5 (ConnectX-4 and later), ixgbe (Intel 82599/X520, X540, X550) and i40e (X710) ship in the mainline Linux kernel. This is why an end-of-life card can still be a sane purchase, and it is a documented fact rather than a forum claim.
3. DatacenterDisk - Live catalogue - NIC, DAC and transceiver listings (datacenterdisk.com, 2026-08-11)
   Used for: every price on this page, read from our catalogue at request time. Seeded 11 August 2026: 24 network cards across 6 models, 24 DAC cables, 8 transceivers. Every card is split tier 1 (the listing is that part) or tier 2 (a third-party board asserting that silicon).
4. DatacenterDisk - Sourcing note - power figures and compatibility claims (datacenterdisk.com, 2026-08-11)
   Used for: We publish no per-port wattage for either cabling path. The relationship - 10GBASE-T draws more power and runs hotter than SFP+ direct attach - is documented at product level and is stated here. The magnitude is not, because we have not fetched and logged a source we can cite for it. Separately: every 'compatible with' phrase shown on this site is stored as a seller claim at tier 2 and badged wherever it renders. We have not tested any module against any switch.
5. NVIDIA - ConnectX-5, ConnectX-4 Lx and ConnectX-4 EN user manuals - end-of-life status (networking-docs.nvidia.com, 2026-09-13)
   Used for: that NVIDIA's own manuals state "The ConnectX-5 product line has moved to end-of-life" and "The ConnectX-4 Lx product line has moved to end-of-life" in those exact words (connectx5enhw and connectx4lxhw respectively, both dated 2026). The standard ConnectX-4 EN manual (connectx4enhw) carries an "EOL'd Ordering Part Numbers" table for every MCX413A/414A/415A/416A SKU but not the same plain-English banner sentence - stated as that asymmetry rather than smoothed into one claim. Also the per-SKU PCIe generation and lane count (PCIe 3.0 x8 or x16 depending on SKU; PCIe 3.0/4.0 on ConnectX-5 Ex variants) from the same manuals.
6. NVIDIA - Linux Kernel Upstream Release Notes - driver and firmware support table (networking-docs.nvidia.com, 2026-09-13)
   Used for: that ConnectX-4, ConnectX-4 Lx and ConnectX-5 all use the mlx5 driver family per NVIDIA's own "Supported Uplinks to Servers" table, dated June 2026 - current documentation, confirming the in-kernel driver is still maintained for hardware NVIDIA itself calls end-of-life for ordering. Also that NVIDIA's current DOCA-Host device list (docs dated September 2026) includes ConnectX-5 and ConnectX-4 Lx but not the standard ConnectX-4 - a real difference in ongoing software-package support between the two, stated as found rather than smoothed over.
7. The Linux kernel project - i40e and ice in-tree Ethernet driver documentation (kernel.org, 2026-09-13)
   Used for: that the i40e driver explicitly lists Intel Ethernet Controller XXV710 as supported hardware alongside X710/XL710/X722 (same page also notes XXV710's speed cannot be forced via ethtool - auto-negotiation only). The companion ice driver page (device_drivers/ethernet/intel/ice.html) is titled for the "800 Series" - the family E810 belongs to - without naming E810 verbatim in the rendered portion, which is stated as the limit of what this specific page confirms rather than stretched into a direct quote. Intel's own ARK product pages did not render in this sourcing pass (see the 100GbE and NIC pages' own note); PCIe generation and EOL status for XXV710 and E810 parts are marked not sourced for that reason.
8. Arista Networks - 7050X and 7050X3 Series switch specifications, and End-of-Sale advisories (arista.com, 2026-09-13)
   Used for: the 7050X family's own published figures: "10GbE Typical Power: 1.2W per port", and for the 7050QX-32S specifically "Typical Power Draw: 150W (4.5W per port)" - the only per-port power figures this cluster publishes, because they are the only ones a vendor datasheet actually rendered and stated. Also Arista's own End-of-Sale advisory archive (arista.com/en/support/advisories-notices/endofsale), which carries a dated 2016 end-of-sale notice for "Select Models of the Arista 7050SX, 7050TX and 7050QX Series" and, separately, 2026-dated end-of-sale notices for the newer 7050SX3-48YC12 and 7050SX3-48YC8/48C8 models - a used 7050-family switch may be running silicon its own maker has since end-of-saled, stated with the notice's own date rather than ours.
9. DatacenterDisk - Live catalogue and sourcing note - 25/40/100GbE cluster (datacenterdisk.com, 2026-09-13)
   Used for: every price in this cluster's tables, read from our catalogue at request time. Seeded 13 September 2026: 12 NICs across 3 models (ConnectX-5, ConnectX-4, Intel E810), 40 DAC cables (25G/40G/100G including breakout), 18 transceivers, 11 used-enterprise and current-SMB switches. Two vendor documentation gaps stated plainly rather than filled: NVIDIA/Mellanox's per-model switch datasheets (SN2010/SN2100/SN2410/SN2700) did not render in this sourcing pass beyond a series-level marketing page, so those four switches carry no sourced power, acoustic or EOL figures; Intel's ark.intel.com did not render at all in this pass, so XXV710 and E810 PCIe generation and formal EOL status are marked not sourced rather than assumed from the 700/800-series family pattern.