25/40/100GbE Cabling - DAC, AOC and Breakout, by Standard

DAC vs AOC vs transceiver-plus-fibre, at every speed here

The same three-way choice the 10GbE cluster documents for SFP+ repeats at each speed in this tier, because it is a property of the connector families, not the speed. A passive direct-attach copper cable has both transceiver ends moulded on permanently - one object, no modules to match, nothing to be rejected for identifying wrongly. It is the cheapest path at every speed and what most short builds between machines you own should use.

An active optical cable packages optics and fibre into the same kind of sealed, fixed-length object as a DAC, trading a higher price for much longer reach. Separate transceivers plus a fibre patch lead cost the most per link and are the only option that scales to real distance with parts that can be swapped independently - a module can be replaced without replacing the fibre run, and vice versa.

Passive copper's reach ceiling is shorter at higher speeds - a documented consequence of the signalling getting more demanding as the rate goes up, not a quality difference between makers. Check the specific listing's stated length rather than assuming the 10GbE cluster's roughly seven-metre practical ceiling holds unchanged at 25G, 40G or 100G.

Breakout cabling: what splits into what

A QSFP28 100G port is, per the standard, four independent 25G lanes bundled into one physical connector. A 100G-to-4x25G breakout DAC has one QSFP28 end and four separate SFP28 legs, wired lane-to-leg rather than converting anything - which is why the four legs go to four different devices rather than giving one device four times the bandwidth.

A QSFP+ 40G port is the same idea one tier down: four 10G lanes in one connector, and a 40G-to-4x10G breakout DAC splits it into four SFP+ legs. Both breakout shapes are standard, documented port behaviour, not a workaround - and both appear as live, priced listings in the tables below.

Whether a specific card or switch port actually supports breaking out is a per-model fact stated in that device's own documentation (see each switch and card's own page in this cluster for what we could source), not something the connector alone guarantees. Confirm before buying a breakout cable expecting a specific port to split.

Vendor coding, at this tier

The same vendor-coding reality the 10GbE cluster documents for SFP+ modules applies here: a transceiver or DAC's moulded ends identify themselves to the port, and equipment enforcing vendor coding can refuse one that does not identify as an approved part. This is documented product-level behaviour, not folklore, and it is reported more often for optical modules than for DAC cables.

Every 'compatible with' phrase in the tables below is the seller's own claim about how their part identifies itself, recorded and badged as a claim rather than verified by us. We have not tested any module or cable against any specific switch or card - the same limit the 10GbE cluster states for its own tables.

The practical mitigation is unchanged from one tier down: buy from a seller with a returns policy if using third-party optics, check whether your switch or card has a setting to accept unapproved modules, and prefer a direct-attach cable for a short run between machines you own, since there is no module identity to reject in the first place.

SFP28 direct-attach cables

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.

SFP28 transceivers and active optical cables

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+ direct-attach cables (straight and 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.

QSFP28 direct-attach cables (straight and 100G-to-4x25G 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.

QSFP28 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.

Where to go next

The 25GbE hub, 40GbE and 100GbE each price a complete build using these cables live · The 10GbE cluster's DAC page and transceivers page cover SFP+ specifically, one tier down · ConnectX-5, ConnectX-4 and Intel E810 are the cards these cables plug into.

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.