Explanation
Broadcast radiation refers to the processing that is required every time a broadcast is received on a host.Although IP is very efficient from a broadcast perspective when compared to traditional protocols such as Novell Internetwork Packet Exchange (IPX) Service Advertising Protocol (SAP), virtual machines and the vswitch implementation require special consideration. Because the vswitch is software based, as broadcastsare received the vswitch must interrupt the server CPU to change contexts to enable the vswitch to processthe packet. After the vswitch has determined that the packet is a broadcast, it copies the packet to all theVMNICs, which then pass the broadcast packet up the stack to process. This processing overhead can have a tangible effect on overall server performance if a single domain is hosting a large number of virtual machines.
Note: This overhead effect is not a limitation of the vswitch implementation. It is a result of the software-basednature of the vswitch embedded in the ESX hypervisor.
ference:
https://www.cisco.com/c/en/us/solutions/collateral/data-center-virtualization/net_implementation_white_paper09