Direct-Attach Cables

Which DAC fits your ports

Choose a DAC by the connector on both ports and the link speed, then take the shortest length that reaches: SFP+ for 10G, SFP28 for 25G, QSFP+ for 40G and QSFP28 for 100G, with a breakout cable when one fast port feeds four slower ones. The length ranges below are Cisco's for its own cables; Dell's cables come in their own lengths, so check the length on each Dell listing.

A breakout cable splits one QSFP port into four SFP-class ports, which lets a 40G or 100G switch port feed four servers.

Passive DAC, active DAC or AOC

A passive DAC is the shortest and lowest-power link, an active DAC goes a little further, and an active optical cable (AOC) swaps the copper for fiber while keeping the fixed plugs. Cisco's data sheets give these figures:

Past the reach of a cable, fiber and Optical Transceivers take over, such as 10GBASE-SR SFP+ or 40G QSFP+ optics.

Coding, InfiniBand and related pages

Buy a DAC made or coded for the equipment it connects: Cisco's SFP+ data sheet, which covers its twinax cables alongside its optics, says the Cisco quality ID feature lets a Cisco platform identify whether a module is certified and tested by Cisco. Cisco's own twinax carries that coding, and cables with Dell part numbers are Dell Networking parts to match Dell Networking switches. Searching by Cisco part number? The Cisco SFP-H10GB-CU3M is Cisco's 3 m passive twinax cable. QSFP copper built for InfiniBand links is its own class, and InfiniBand vs Ethernet explains how the two fabrics differ. Switch stacking cables have their own page, Stacking Cables, and every cable family sits under Cabling.

DAC cable questions

Passive or active DAC: which do I need?

Go by length. Passive twinax covers the short runs, 1 to 5 m for Cisco's 10G and 25G cables and 0.5 to 5 m for its 40G cables, at about 0.1 W. Active twinax extends a 10G or 40G link to 7 or 10 m at about 1 W, and beyond that an active optical cable or two optics with fiber is the better fit. Order the shortest cable that reaches.

Can I use a DAC between two different switch brands?

Only if each switch accepts the end plugged into it. Switches check the module they see: Cisco's quality ID lets a Cisco platform identify whether a module is Cisco-certified, and Cisco's Catalyst guide says the switch reads the module's EEPROM and can error-disable a port whose vendor data fails. For two brands, order a cable coded for the switch at each end, or ask us to match one before you order.