Compatibility check 1: failover versus load-balancing behavior
For dual-wan routers, record the exact value, standard, measurement, or supported condition behind failover versus load-balancing behavior before checkout. A broad category label does not prove that the selected variant fits. Confirm the manufacturer, complete model, hardware revision, region, port layout, firmware branch, and included power hardware rather than assuming similarly named products share limits.
Compatibility check 2: health-check target and timing
Test health-check target and timing across the actual topology, client mix, cable path, traffic load, and recovery window—not a product-photo setup. If this dual-wan routers fit depends on specific cabling, transceivers, power budgets, adapters, controller software, service tiers, or client capabilities, confirm the exact part, service, or behavior as part of compatibility.
Compatibility checks 3 and 4: session interruption during switchover; modem, DNS, and inbound-service constraints
For dual-wan routers, session interruption during switchover and modem, DNS, and inbound-service constraints are the limiting conditions most likely to surface only after installation. Measure the smallest clearance, weakest connection, least compatible user or device, and the most demanding normal task. Passing an ideal bench test is not enough.
Prove fit in a reversible order
Use this sequence: bring up both WAN links independently, set health checks, test a controlled failure, and document which services must recover manually. Keep labels, packaging, manuals, and the previous system until the product works through normal use and a recovery test. Photograph wiring, measurements, or assembly states that would be difficult to reconstruct.
A failed fit check is a stop signal
Stop when the second link shares the same physical failure path, sessions cannot tolerate a new public IP, or manual phone tethering is enough for rare outages. Do not repair a fundamental mismatch with unapproved accessories, copied settings, or community anecdotes. Use a standard router with manual failover when it meets the job with a clearer compatibility path.