WS-C3750X-24P-S Replacement: Migrate to Catalyst 3850

If you still have a Cisco Catalyst 3750-X 24-port PoE switch (PID WS-C3750X-24P-S) carrying production traffic, it is running well past every Cisco support boundary. End-of-Sale was October 30, 2016; software maintenance ended October 30, 2017; and the Last Date of Support (LDoS) passed on October 31, 2021. That last date is the one that matters most: as of today the platform has had no security patches for years and is entirely outside Cisco's TAC and RMA umbrella. This guide explains what those milestones mean operationally and lays out a concrete, low-risk migration to the named successor, the Catalyst 3850 24-port PoE IP Base (WS-C3850-24P-S).

Why a 3750-X past LDoS is a liability, not just an old switch

A switch that still forwards packets can feel like a switch that is still fine. It is not. After LDoS, Cisco's PSIRT no longer issues fixed software for the 3750-X, so any new vulnerability disclosed in its IOS train, including ones that affect the broader IOS code base, will never be patched on this hardware. There is no engineering escalation path through TAC and no advance hardware replacement, so a failed power supply or a dead supervisor becomes a scavenge-the-spares-shelf problem rather than a next-business-day RMA.

What each milestone date actually means

• End-of-Sale (2016-10-30): Cisco stopped selling the WS-C3750X-24P-S new. Any unit acquired after this is used, refurbished, or gray-market. The lifecycle clock started here.
• End of SW Maintenance (2017-10-30): the last date Cisco released maintenance and bug-fix software. After this, only severe security fixes were considered, and only until LDoS.
• Last Date of Support (2021-10-31): the hard stop. No TAC, no RMA, no PSIRT fixes, regardless of any SmartNet contract you may still be paying for. Support contracts cannot be renewed past this date.

The replacement: WS-C3850-24P-S and what it buys you

Cisco's own bulletin named the Catalyst 3850 24-port (WS-C3850-24P-S) as the direct successor, and it is a meaningful generational jump rather than a sidegrade. Both switches present the same physical edge: 24 ports of 10/100/1000 with 802.3at PoE+ at up to 30W per port. What changes is everything behind the ports.

• Stacking bandwidth: StackWise Plus on the 3750-X is a 32 Gbps ring. The 3850 uses StackWise-480, a 480 Gbps backplane, a 15x increase that removes the stack interconnect as a bottleneck and supports up to nine members.
• Operating system: the 3750-X runs classic IOS; the 3850 runs IOS-XE, a Linux-based, modular OS with patchability, model-driven telemetry (NETCONF/YANG), and a clean path toward programmability and ISSU-style updates.
• Wired-plus-wireless convergence: the 3850 has an integrated wireless LAN controller that can terminate up to 50 access points and 2000 clients directly on the switch, something the 3750-X simply cannot do.
• Uplinks: the 3850 network modules add 10G SFP+ and 40G QSFP+ options, versus the 3750-X's C3KX-NM ceiling of 2x10G, giving you real headroom for aggregation.
• PoE headroom: the 3850-24P delivers a 435W PoE+ budget on one supply, expandable with a second power supply, comfortably covering a modern edge of Wi-Fi 6 APs, IP phones, and cameras.

The licensing shift you must plan for

The 3750-X used the old per-image IP Base / IP Services model with right-to-use licensing baked into the software train. The 3850 moves to the IOS-XE world: IP Base and IP Services as on-box licenses, and later releases adopting Cisco Smart Licensing and the Cisco DNA subscription tiers. The practical implication is that you no longer treat the license as a static attribute of the box. You will register the 3850 to a Smart Account (or a Smart Software Manager On-Prem satellite for air-gapped environments), and DNA Essentials or Advantage entitlements ride alongside the hardware. Build the Smart Account and entitlement mapping into the project up front so switches do not land in a non-compliant licensing state on day one.

A practical migration plan

1. Assess and inventory

Catalog every 3750-X stack: member count, IP Base vs IP Services, uplink module type, PoE draw, and the running config size. Pull show version, show inventory, and show power inline from each stack so you size the 3850 supplies and uplinks correctly. Use our Cisco EoL hub to cross-check any co-located gear that is also aging out, since refreshing the access layer is the natural moment to retire end-of-life uplinks and aggregation switches in the same window.

2. Establish licensing and config parity

Stand up the Smart Account and map each 3750-X feature set to the equivalent 3850 license tier (IP Base to Network Essentials-class, IP Services to Advantage-class for routing-heavy stacks). Then translate the configuration: most IOS CLI carries directly to IOS-XE, but validate the differences, including interface naming under the new platform, the QoS model (the 3850 uses MQC throughout), and any embedded event manager or netflow that needs reworking. Build the target config in a lab or on a single 3850 before touching production.

3. Plan the physical layer

Both are 1RU, but the cabling and power are not drop-in. The 3750-X's StackWise Plus cables and StackPower cables do not fit the 3850; you will use StackWise-480 and the 3850's own redundant power supplies. Confirm rack PDU capacity for the higher PoE budget, reuse compatible 1G/10G optics where the compatibility matrix allows, and order the correct 3850 network module for your uplinks rather than assuming the old C3KX-NM transfers.

4. Phased cutover and secure decommission

Migrate one closet or stack at a time during a maintenance window. Pre-stage the 3850 with the validated config, move uplinks first to verify the upstream path, then shift access ports in batches, watching PoE negotiation and spanning-tree convergence as you go. Keep the old stack powered but isolated until the new one is proven, then decommission it securely: wipe the configuration and VLAN database, remove from monitoring and the asset register, and dispose through a process that meets NIST SP 800-88 media-sanitization requirements for any unit that held sensitive config or keys.

Procurement notes for government and enterprise buyers

Source the replacement from an authorized partner so you get TAA-compliant, traceable hardware with valid Cisco licensing rather than gray-market stock that can fail an audit or arrive unlicensed. As an authorized Cisco partner, uniqcli supplies TAA-compliant 3850 (and current-generation Catalyst 9300) units, accepts the Government Purchase Card (GPC) for in-threshold orders, and supports DoDIN APL sourcing paths. Note that the 3850 itself is now end-of-sale with an LDoS of October 30, 2025, so for new purchases we will also quote the Catalyst 9300 successor so you can weigh budget against lifecycle. Lead times on refresh hardware move with demand, so it is worth locking quantities early.

You can review the full lifecycle detail for this exact unit on our WS-C3750X-24P-S end-of-life page, browse the replacement in our catalog, and when you are ready to scope the refresh, get a quote and we will size the 3850 or 9300 path, licensing, optics, and cutover plan for your environment.