Dell Networking S4128F-ON 10GbE Switch

The Dell Networking S4128F-ON is a 1U open-networking top-of-rack switch with 28x 10GbE SFP+, 2x 100GbE QSFP28. It moves 960 Gbps through a non-blocking cut-through fabric at 720 Mpps with 800 ns port-to-port latency.

Where the S4128F-ON sits in a data center

This is the fibre and direct-attach member of its family. The S4128F-ON presents 28 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 800 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 2x 100GbE QSFP28 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

28 SFP+ ports plus 4x10GbE breakout on each of the 2 QSFP28 ports (8) reaches the 36-port maximum 10GbE density Dell publishes for this model.

Fixed ports: 28x 10GbE SFP+, 2x 100GbE QSFP28. That breakout capability is the reason a 28-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 S4128F-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 S4128F-ON

Dell EMC Networking OS10 Enterprise Edition (OS10.3); ONIE-enabled for 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.

The scale figures for this chassis - 272K MAC addresses, 200K IPv4 routes, 130K IPv6 routes - are OS10 Enterprise Edition numbers in the scaled L2/L3 profiles. OS10 is the software this generation was designed around.

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.

Within the S4100 generation, the 28-port models are the right size for a half-populated rack or a small colocation cage. They give up half the access ports of the 48-port models and two of the four QSFP28 uplinks, and the fabric drops from 1.76 Tbps to 960 Gbps - but the feature set, the operating system and the scale tables are identical.

Condition, testing and warranty

Every S4128F-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