A broadcast address is the last IPv4 address in a network or subnet. Every bit in its host portion is 1, so it cannot be assigned to a host. Devices can use it to send one message to all hosts in that network. section 7.3.3
192.168.100.0/24
A /24 leaves eight host bits. The network address is 192.168.100.0, and setting all eight host bits to 1 produces the broadcast address 192.168.100.255. The usable host range is 192.168.100.1 through 192.168.100.254. section 7.3.3
Identify the broadcast address by checking these relationships:
- Find the subnet’s network address, then locate the final address before the next subnet begins. section 11.2.1
- Treat the broadcast address as unusable for hosts; subtracting two from the total addresses accounts for both the network and broadcast addresses. section 7.3.3
Do not confuse a subnet’s directed broadcast address with 255.255.255.255, a specially reserved address usually used to reach all hosts on the local network. A specific subnet broadcast, such as 192.168.100.255, identifies all hosts in 192.168.100.0/24. section 7.3.3 section 7.3.2
