Broadcast radiation consists of network traffic sent to all hosts on a subnet, such as ARP requests, routing updates, and service discovery protocols. While normal in small amounts, excessive radiation consumes bandwidth and forces every connected device to process the packets, degrading overall network performance. Network engineers use VLANs to contain this traffic and keep domains small.
The CPU spikes on the older switches are just from handling the constant broadcast radiation across that massive flat subnet.
Related terms
Broadcast storm
A cascading network failure caused by broadcast packets endlessly replicating across redundant links.
Router
A network device that forwards data packets between computer networks.
Ethernet card
An expansion board that provides a physical connection between a computer host and a local area network.