Short answer: The Cisco Catalyst WS-C3850-48XS-F-S and WS-C3850-48XS-S are the same 48-port 10G SFP+ switch with four 40G QSFP+ uplinks and the IP Base license. The only difference is airflow direction. The -F-S is back-to-front (FAN-T3-F fans, PWR-C3-750WAC-F power supplies). The 48XS-S is front-to-back (FAN-T3-R fans, PWR-C3-750WAC-R power supplies). Order the one that matches your rack's hot-aisle/cold-aisle layout. Resilient Tec has the refurbished WS-C3850-48XS-F-S in stock for $1,450, with free US shipping and a lifetime warranty.
Why this part number gets mixed up
The "F" in WS-C3850-48XS-F-S looks like it could stand for "front," and some listings online describe the -F-S as front-to-back. Cisco's own part descriptions say otherwise: Cisco lists the FAN-T3-F as the Catalyst 3850 Type 3 back to front cooling fan and the FAN-T3-R as the front to back fan, and the PWR-C3-750WAC-F and PWR-C3-750WAC-R power supplies follow the same pattern. On these models, -F means back-to-front.
Side-by-side comparison
| WS-C3850-48XS-F-S | WS-C3850-48XS-S | |
|---|---|---|
| Airflow | Back-to-front | Front-to-back |
| Fan modules | 3 × FAN-T3-F | 3 × FAN-T3-R |
| Power supply | PWR-C3-750WAC-F | PWR-C3-750WAC-R |
| Downlinks | 48 × 1/10G SFP+ | 48 × 1/10G SFP+ |
| Uplinks | 4 × 40G QSFP+ | 4 × 40G QSFP+ |
| License | IP Base | IP Base |
| Switching capacity | 1,280 Gbps | 1,280 Gbps |
| Form factor | 1RU | 1RU |
How to tell which one you have
- Check the fan modules. Each of the three hot-swappable fans is labeled FAN-T3-F (back-to-front) or FAN-T3-R (front-to-back).
- Check the power supply label. PWR-C3-750WAC-F is back-to-front; PWR-C3-750WAC-R is front-to-back.
- Check the chassis PID label for the exact product ID.
Every fan and power supply in the switch should carry the same suffix. A switch with mixed -F and -R modules is fighting its own airflow and will run hot. When buying used or refurbished, ask the seller to confirm the fan and PSU part numbers, not just the chassis model.
Which one should you buy?
Cisco defines the port side as the front of the switch. Choose by where the port side faces in your rack:
- Ports face the hot aisle (common in top-of-rack setups where switch ports face the server rear): choose back-to-front, WS-C3850-48XS-F-S.
- Ports face the cold aisle: choose front-to-back, WS-C3850-48XS-S.
If you add a second power supply for redundancy, buy the same airflow type as the one installed. For an -F-S switch, that is another PWR-C3-750WAC-F.
Lifecycle: what buyers should know in 2026
Cisco announced end-of-sale for the Catalyst 3850 fiber models with a last order date of April 30, 2022. The last date to renew a Cisco service contract was July 29, 2026, and Cisco's Last Date of Support, including security fixes, is April 30, 2027. Cisco names the Catalyst C9500-48Y4C as the replacement.
That means you can no longer put a new SmartNet contract on a 3850-48XS. Resilient Tec covers every switch it sells with a lifetime warranty, including advance replacement when the part is in stock, so support continues after Cisco's ends.
Frequently asked questions
Is the WS-C3850-48XS-F-S front-to-back or back-to-front?
Back-to-front. It ships with FAN-T3-F fans and PWR-C3-750WAC-F power supplies, which Cisco lists as back-to-front cooling parts.
Can I use a PWR-C3-750WAC-R power supply in a WS-C3850-48XS-F-S?
Don't. Mixing airflow directions in one chassis works against the switch's cooling. Use PWR-C3-750WAC-F power supplies in the -F-S.
Is there any feature difference between the two models?
No. Ports, uplinks, switching capacity, and the IP Base license are the same. Only the airflow direction differs.
Can I still buy SmartNet for a Catalyst 3850-48XS?
No. Cisco's final service contract renewal date for these models was July 29, 2026, and the Last Date of Support is April 30, 2027.
Where can I buy a WS-C3850-48XS-F-S, and how much does it cost?
Resilient Tec sells the refurbished, tested WS-C3850-48XS-F-S for $1,450, in stock, with free US shipping and a lifetime warranty. Buy it here.
Pairing the 48XS with uplinks? The Cisco Catalyst hub lists every 10G SFP+ and 40G QSFP+ optic and DAC we stock for it, plus the CVR-QSFP-SFP10G adapter.
You Might Also Need
- Cisco SFP-H10GB-CU1M 10G SFP+ DAC, 1m (New): $82.00. Server-to-switch 10G links.
- Cisco SFP-H10GB-CU3M 10G SFP+ DAC, 3m (New): $79.33. Longer in-rack 10G runs.
- Cisco QSFP-40G-SR4 40G QSFP+ Transceiver (Refurbished): $31.29. 40G uplinks over multimode fiber.
- Cisco QSFP-40/100-SRBD BiDi Transceiver (Refurbished): $45.00. 40G uplinks over existing duplex LC fiber.
- Cisco QSFP-H40G-CU1M 40G QSFP+ DAC, 1m (Refurbished): $144.77. Short 40G switch-to-switch links.
Ready to Buy?
Cisco Catalyst WS-C3850-48XS-F-S, Refurbished/Tested: $1,450. In stock at Resilient Tec. Includes 3 × FAN-T3-F, 1 × PWR-C3-750WAC-F, rack mount kit, console cable, and power cord. Free US shipping, lifetime warranty.