Key Technical Specifications
| Parameter | Specification |
|---|---|
| Model / Part Number | A4H124-24TX / P0973JM |
| Port Configuration | 24 × 10/100 Mbps RJ-45 copper ports |
| Uplink / Stacking | 2 × SFP slots + 2 × 10/100/1000 Mbps RJ-45 uplink/stacking ports (per A4H124-24 family spec) |
| Switching Capacity | 12.8 Gbps (switch); 102.4 Gbps (stacked) |
| Forwarding Rate | 9.5 Mpps (switch); 76.2 Mpps (stacked) |
| MAC Address Table | 16,000 entries |
| Supported Protocols | TCP/IP, UDP, Modbus TCP, Foxboro I/A Series protocols, VLAN (802.1Q), QoS |
| Redundancy | External RPS (Redundant Power Supply) support; stacking capability |
| Operating Temperature | −20°C to +60°C (−4°F to 140°F) |
| Humidity | 5% to 95% non-condensing |
| Protection Rating | IP20 (panel/cabinet mount) |
| Safety Standards | UL 60950-1, CSA 22.1 60950, EN 60950-1, IEC 60950-1 |
| Power Input | DC 24 V (±10%) or AC variant depending on configuration; verify nameplate |
Product Introduction
I’ve pulled this exact switch out of Foxboro I/A Series racks more times than I’d like to count. The A4H124-24TX isn’t fancy — it’s a 24-port 10/100 managed switch that sits between your DCS controllers, operator stations, and field devices. It doesn’t run your process logic. But when it dies, the entire node goes dark, and suddenly you’re troubleshooting a “DCS communication failure” that’s really just a dead Ethernet port.The P0973JM designation is Foxboro’s ordering code for this specific A4H124-24TX configuration. It delivers 12.8 Gbps of non-blocking switching capacity and supports stacking up to 102.4 Gbps, which was solid for its era. The 16,000-entry MAC table means it can handle dense I/A Series node deployments without flooding. VLAN and QoS support let you segment control traffic from general plant LAN traffic — something I always recommend doing, even if the original installer didn’t bother. One thing to watch: the A4H124-24TX is a 10/100 switch with gigabit uplinks. If your plant has migrated to an all-gigabit backbone, this unit will bottleneck at the edge. It’ll still work, but don’t expect it to feed a high-bandwidth historian stream.
Quality SOP & Tech Pitfalls
The Lab Report (SOP):
- Visual & Counterfeit Check: Inspect the front panel for model “A4H124-24TX” and P/N “P0973JM.” Check for burnt ports, swollen capacitors, or resoldered RJ-45 jacks.
- Port Continuity Test: Use a Fluke cable tester or equivalent to verify all 24 RJ-45 ports establish link with a known-good device.
- Power-On Test: Apply rated power (verify AC or DC per nameplate); confirm PWR LED is steady and SYS/RUN LED is normal.
- Managed Function Test: Connect via console or web interface; verify firmware boots, VLAN/QoS configuration loads, and all ports respond to SNMP queries.
- Firmware Revision Logging: Record the firmware version (e.g., 03.xx.xx); cross-check against your existing stack members for compatibility.
- Anti-Static Sealing: Bag in ESD packaging with test record, firmware version, and serial number.
The Engineer’s Warning (Pitfalls):Two traps I see regularly. First, someone replaces the switch without documenting the VLAN assignments and port configurations. The new unit boots fine, all link lights are green, but the DCS controllers can’t talk because the management VLAN was never recreated. Export your config before you pull the old switch.Second, the firmware mismatch. If you’re stacking multiple A4 switches, they need to run compatible firmware versions. I once watched a four-switch stack refuse to form because one replacement unit was running a three-major-revisions-older image. The stack split, half the nodes went offline, and it took two hours to TFTP the correct image onto the replacement. Always check firmware before installation.
Installation & Configuration Guide
30-Minute Swap Procedure:
- Pre-Installation (⚠️ Critical):
- Notify operations that network connectivity to affected DCS nodes will be interrupted.
- Export and save the current switch configuration (VLANs, port assignments, SNMP community strings, IP address).
- Photograph the existing unit’s nameplate, firmware version, and port patch layout.
- Confirm the replacement model matches: A4H124-24TX, P/N P0973JM.
- Removal:
- Label all Ethernet cables before disconnecting.
- If stacked, remove stacking cables last to avoid disrupting remaining stack members.
- Release mounting hardware and slide the unit out.
- Installation:
- Verify model A4H124-24TX and P/N P0973JM on the replacement unit.
- Mount the unit and secure all fasteners.
- Reconnect Ethernet cables per your labels.
- Reconnect stacking cables if applicable.
- Power-On & Testing:
- Apply power; verify PWR and SYS LEDs are normal.
- Load the saved configuration via console, web interface, or TFTP.
- Verify all 24 ports establish link with connected devices.
- Confirm DCS node communication is restored (check I/A Series node status).
- If stacking, verify stack membership and firmware compatibility.
Compatible Replacement Models
| Tier | Model | Notes |
|---|---|---|
| ✅ Drop-in | A4H124-24TX (P0973JM) | Exact match. Verify firmware revision matches existing stack. |
| ⚠️ Software Compatible | A4H124-24P (P0973JN or similar) | Adds 802.3af PoE on 24 ports. Same form factor and management. Requires config migration and PoE budget verification. |
| ⚠️ Upgrade Path | Extreme Networks A4H124-24 (current generation) | Successor platform. Same A4 family, but firmware and CLI may differ. Plan for config translation and firmware upgrade. |
| ❌ Hardware Mod Required | A4H124-24FX (P0973UN) | Fiber-port variant. Different physical interfaces — requires fiber patching changes. Not a direct copper-to-copper swap. |
Frequently Asked Questions (FAQ)
Q1: Can I hot-swap this switch in a live Foxboro I/A Series network?
Not cleanly. Unlike a redundant power supply or a hot-swappable I/O card, replacing a managed switch interrupts all connected nodes. If you have redundant network paths (dual NICs on controllers, ring topology), you can swap one side at a time. Otherwise, plan a maintenance window.Q2: Is P0973JM the same as A4H124-24TX?
Yes. P0973JM is the Foxboro I/A Series ordering code for the A4H124-24TX hardware. You’ll see both on the nameplate. If a supplier only lists one or the other, ask for a photo of the actual unit to confirm.Q3: Will my VLAN and port configuration survive a replacement?
No. The configuration lives in the switch’s flash memory, not on a central server. You must export the config from the old unit (or from your backup) and load it onto the replacement. This is the single most common cause of post-replacement downtime.Q4: Can I stack this with other A4 switches?
Yes. The A4H124-24TX supports stacking via the two dedicated 10/100/1000 Mbps uplink/stacking ports. All stack members should run the same or compatible firmware versions. Mismatched firmware is the top cause of stack formation failures.Q5: Does it support PoE?
The standard A4H124-24TX (P0973JM) does not provide PoE. If you need PoE, look for the A4H124-24P variant. Don’t assume a P0973JM unit can power IP phones or wireless APs — it can’t.Q6: What firmware version should I run?
Match the firmware version of your existing stack members or the unit you’re replacing. If you’re running a standalone unit, use the latest stable release supported by your I/A Series platform. Check the Extreme Networks (formerly Enterasys) documentation for the current recommended version.Q7: What warranty should I expect?
Typical surplus stock carries a 12-month defect warranty. For a network-critical switch, test all 24 ports and verify configuration loading within the first week. A switch that passes a basic power-on test can still have marginal RJ-45 contacts that cause intermittent link drops under vibration.
