How it works

A Direct Attach Copper cable (DAC) is twinax copper with SFP+, SFP28, or QSFP cages molded onto both ends, so two switches or a NIC and a switch can run a short high-speed Ethernet link without buying separate optical transceivers. Passive DAC is the common rack pick: the hosts’ cages drive the copper directly, power draw stays low, and latency is tiny. Active DAC adds electronics in the cable for slightly longer copper runs. Neither is a fiber AOC (active optical cable)—AOCs still look like DAC form-factor but carry light inside a thin fiber jacket for longer aisles.

The cages follow the same MSA footprint as hot-pluggable SFP+ optics, so you seat a DAC the same way you seat a module—except the “module” is permanently attached to the twinax. Typical 10G SFP+ passive lengths are 0.5–3 m for top-of-rack or adjacent-rack jumps; longer copper usually means thicker gauge, higher power, or a move to optics. Match speed and form factor on both ends (10G SFP+ to 10G SFP+, 25G SFP28 to SFP28, and so on). Vendor EEPROM coding can matter on picky switches—MSA “open” or Cisco-coded third-party DACs cover most home-lab and SMB gear.

Think of DAC as an Ethernet patch cord that already includes the pluggable ends, built for the short hops inside a rack instead of across a building.

When it matters

It matters when two SFP+/QSFP ports sit within a few meters and you want 10G (or faster) without the cost and optics inventory of fiber modules—not when the run crosses rooms or floors. Prefer DAC for switch stacking, NIC-to-ToR, or lab benches where a short twinax is cleaner than RJ45 multi-gig adapters. Skip DAC when you need longer reach, electrical isolation, or the hosts only expose copper RJ45—then use fiber optics, AOC, or a multi-gig copper path instead.

DAC does not replace link aggregation: if you need more aggregate bandwidth or failover across several ports, pair short DAC (or copper) members with LACP. SFP+ cages and 2.5/5/10G copper are related glossary topics when you are choosing between DAC and RJ45 multi-gig uplinks.

A short Cable Matters SFP+ DAC for adjacent ports, plus a 3 m 10Gtek twinax when the jump spans a bit more of the rack.

The Cable Matters 10Gbps DAC Twinax SFP+ Cable (0.5 m) is a passive 10GBASE-CU twinax for very short switch-to-switch or NIC-to-switch hops. View on Amazon when the ports sit in the same rack unit stack or neighboring chassis.

The 10Gtek SFP+ DAC Twinax Cable (3 m) is a passive 10G Direct Attach copper patch aimed at Intel-coded and many open SFP+ ports. View on Amazon when you need a longer in-rack twinax without moving to fiber optics.

For bundling multiple Ethernet members for bandwidth and failover, see LACP. For copper category cabling on RJ45 paths, see Cat6.