Dell Networking S4048-ON 10GbE Switch

The Dell Networking S4048-ON is a 1U open-networking top-of-rack switch with 48x 10GbE SFP+, 6x 40GbE QSFP+. It moves 1.44 Tbps full-duplex (720 Gbps half-duplex) through a non-blocking cut-through fabric at 1080 Mpps with Sub-650 ns port-to-port latency.

Where the S4048-ON sits in a data center

This is the fibre and direct-attach member of its family. The S4048-ON presents 48 ports of SFP+, which take either optical transceivers or passive twinax DAC cables. Inside a rack, DAC is the normal choice - it is cheaper than optics, draws almost no power and keeps port-to-port latency at Sub-650 ns. Optics take over for cross-row and cross-room runs.

Deployed as a top-of-rack leaf, the fixed ports face the servers and the 6x 40GbE QSFP+ face the spine. In a two-tier leaf-spine build a pair of these switches sits in each rack running VLT, so each server can dual-home with LACP into two physically separate chassis and survive the loss of either one. VLT is the reason there is no stacking port on this switch: Dell's S-Series uses multi-chassis link aggregation rather than a stack ring, which means the two peers keep independent control planes and can be upgraded one at a time without dropping the rack.

Port layout and breakout math

Each of the 6 QSFP+ uplinks breaks out to 4x 10GbE with a breakout cable, so 48 fixed SFP+ ports plus 24 broken-out ports reach the 72-port 10GbE maximum Dell publishes for this switch.

Fixed ports: 48x 10 Gigabit Ethernet SFP+, 6x 40 Gigabit Ethernet QSFP+. That breakout capability is the reason a 48-port switch is worth quoting against a larger chassis - the uplinks are not dead weight if you do not need them at their native speed, they convert into usable access ports with a passive breakout cable.

Airflow: standard and reverse builds

This listing covers both airflow builds of the S4048-ON. Select the direction under the Airflow option: air direction is set by the power supplies and fan modules physically fitted, so it is chosen when the unit is built rather than switched afterwards. Power supplies and fans must both face the same way - a mismatched pair raises the switch's incompatible-airflow alarm.

Standard airflow (I/O to PSU)

The normal-airflow (NA) build, also written I/O-to-PSU or front-to-back. Air enters at the port face and exhausts at the power-supply end. Fit it when the switch is mounted with its ports facing the hot aisle, which is the conventional orientation in a cold-aisle-containment room where servers also pull from the front.

Airflow is fixed by the power supplies and fan modules that are physically installed, and the two must match each other. If your rack presents the switch ports to the cold aisle, you want the Reverse Airflow option above - converting a chassis in the field means swapping both the PSUs and the fan modules, not flipping a setting.

Reverse airflow (PSU to I/O)

The reverse-airflow (RA) build, sometimes written PSU-to-I/O or back-to-front. Air is drawn in at the power-supply end of the chassis and exhausted out of the port face. Fit it when the switch is mounted with its ports facing the cold aisle - the common arrangement when you want to patch from the front of the rack and keep cabling out of the hot aisle.

Airflow is not a setting. It is determined by the physical power supplies and fan modules installed, and the two must agree: a reverse-airflow chassis needs reverse-airflow PSUs and reverse-airflow fans. Mixing directions makes the switch raise an incompatible-airflow alarm and leaves a stalled thermal path. If your rack is laid out the other way - ports on the hot aisle - order the Normal Airflow option above of trying to reverse this one in the field.

Operating system and licensing on a used S4048-ON

Dell Networking OS9 (FTOS); ONIE-enabled for OS10 or third-party NOS. Because the platform is ONIE-based, the operating system is not welded to the hardware: the switch boots into the ONIE installer and pulls whichever network operating system you point it at. That is the whole premise of Dell's open-networking line and it is what makes these switches practical on the secondary market.

Be precise about which OS you are planning around, because the scale numbers differ. The figures Dell publishes for this chassis - 160K MAC addresses, 128K IPv4 routes - are the OS9 numbers. OS9 (the FTOS lineage) is the software this generation shipped with. OS10 also runs on this hardware and third-party NOS options such as SONiC and Cumulus have historically been supported on the platform.

What a used unit does not carry is an active Dell software entitlement or support contract. Licensing and OS entitlement are handled directly between you and Dell (or the NOS vendor) and are not transferred by the sale of hardware. Plan for that in your build: if you need a licensed, vendor-supported OS10 image, source the entitlement separately. If you are running an open NOS, this is a non-issue and is one of the main reasons buyers choose ONIE hardware secondhand. We describe the hardware condition and back the hardware with a warranty; we make no representation about Dell software support status.

Choosing between the S4000-series models

The suffix letters are the fastest way to read this family. F means SFP+ fibre and direct-attach ports. T means 10GBASE-T copper on RJ45. U means unified ports that run either Ethernet or Fibre Channel. The two-digit number before the letter is the fixed port count - 12, 28, 40 or 48.

The generation gap matters as much as the letter. The S4048-ON and S4048T-ON are the 2014 open-networking wave: 1.44 Tbps of fabric, 1080 Mpps, six 40GbE uplinks and no 100GbE anywhere. The S4100-ON models - S4148F-ON, S4148T-ON, S4128F-ON and S4128T-ON - are the 2017 refresh on Broadcom Maverick silicon: up to 1.76 Tbps, 1320 Mpps, and QSFP28 uplinks that give you real 100GbE and multi-rate 25/50GbE breakout. If you are buying to sit under a 100GbE spine, the S4100 generation is the one that connects to it natively; the S4048 generation tops out at 40GbE.

Above both sits the S4248FB-ON from the S4200-ON series, which trades a few access ports for six QSFP28 uplinks and a much larger control-plane complex - the configuration usually chosen for border-leaf and WAN-edge duty rather than plain server access.

Condition, testing and warranty

Every S4048-ON we ship is refurbished enterprise hardware: inspected, cleaned, powered up and functionally tested before it leaves the building, and supplied with warranty coverage. Configure the power supplies, fan modules, rail kit, console cable and optics you need above and the unit is built to that specification rather than shipped as a bare chassis. If you are matching an existing pair for a VLT peer, tell us the airflow direction and PSU part numbers you already run and we will match them.

Specifications