IPv4 Addressing (Part 2)
Class A network is in the range 0-127 but 0 and 127 ranges are reserved, so the usable range of Class A network is 1-126. Let's see one network for calculating the number of usable addresses for hosts. 192.168.1.0/24 is a Class C network so it has a /24 subnet mask. The host range is 192.168.1.0 - 192.168.1.255. It gives us 256 (2^8) addresses. But there are network and broadcast addresses, so the total number of usable host addresses is 254. The number of hosts per network is
where n is the number of host bits.
IPv4 Configuration
To check the status of the interfaces on the device, you have to enter show ip interface brief command in privileged EXEC mode. It lists the interface name, IP address, method used to assign, status, and protocol of each interface. The status column refers to the Layer 1 state and protocol - to the Layer 2 state. The default status of Cisco routers is administratively down, it is when the shutdown command is applied. Also, you can enter show interfaces command but it displays too much information, so it's better to specify an interface using the same command but followed by the interface name. Besides that, you can see the description of each interface, they are optional but might help in identifying the purpose of each interface. The command is show interfaces description.
To enter interface configuration mode, you have to enter interface followed by the interface name you want to enter in global configuration mode. To configure an IP address - ip address followed by the IP address and subnet mask in dot-decimal notation. And lastly, no shutdown - to enable the interface. The command to configure the description is description followed by the description.
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