Each manufacturer has specific rules for access to firmware, software and drivers for their devices and will make it hard for you as the end user to understand them. It really comes down to how you access the firmware, software and drivers, and the ways you are entitled to that access. Some manufacturers don't require a valid maintenance entitlement to get to the software and just allow access to it via download links. Others may require you to enter a serial number first to validate an entitlement to firmware, software and drivers.
Dell PowerEdge servers
HP ProLiant servers
Lenovo ThinkServer
IBM xSeries
SuperMicro, Quanta and other ODM manufacturers
Cisco Catalyst Switches
Cisco Routers
HP/Aruba Switches
Dell PowerConnect Switches
EMC VNX arrays
NetApp filers
HPE Nimble storage
EMC Unity devices
EMC DataDomain units
IBM Power servers
Sun Microsystems servers
Tape Libraries
HP-UX servers