The current default IP addressing scheme is IP version 4 (IPv4), which uses a 32-bit address field and a 32-bit mask field.
IPv4 addressing can be classful, which uses a specific class (A, B, C) of IP address and an associated default subnet mask. It can also use the class addressing scheme with variable length subnet masks (VLSM). IP addressing can also be configured to use Classless Inter-Domain Routing (CIDR) with a specified prefix length.
The D class of IPv4 addressing is set up for multicast use and uses the 224.0.0.0 to 239.255.255.255 range of addresses. It's normally configured without using a subnet mask.
The E class of IPv4 addressing is set up for experimental use and uses the 240.0.0.0 to 255.255.255.255 range of addresses. It'snormally configured without using a subnet mask.
Automatic Private IP Addressing (APIPA) allows a DHCP client to self-configure an IP address and subnet mask when a DHCP server isn't available. APIPA selects an IPv4 address from 169.254.0.1 through 169.254.255.254, with a subnet mask of 255.255.0.0. APIPA addressing is not routable, and client communications are limited to the local subnet.
Hosts that are connected directly to the Internet and do not use NAT or a proxy server require a unique public IP address.
Hosts that are connected indirectly to the Internet, such as those that use NAT or a proxy server, can be configured to use IP addressing from the Address Allocation for Private Internets ranges or other private IP addressing schemes.
When designing and planning the number of hosts per subnet, you need to plan for optimization of both the number of subnets and the number of hosts per subnet.
The four main types of IP addressing are manual, DHCP dynamic, DHCP reservation, and APIPA.
DHCP reservations are used when the DHCP service doles out IP addresses to host systems that require the same IP address at all times.
DHCP dynamic addressing is the "standard" type of IP addressing in use; host systems receive a random IP address from the scope of available IP addresses for their subnet.
APIPA addressing is used when a small, nonrouted network needs a simple IP addressing solution or when a DHCP server is suddenly unavailable.
