IP ADDRESSING
IP address space in general - inference of Class A/B/C
Before we start - a quick and very basic recap on IP addressing in general.
Every machine on the net has an address. Addresses are 32 bits. These 32 bits are split into two parts - a network number followed by a host address. The 'host address' part is for a number of machines on one physical network - say a bunch of machines connected with a hub or on a single thin ether wire. The network number represents this group of hosts as a single unit, and routers need to know these network numbers to send data from one net to another.
Just where the network/host split is made is arbitrary. There's no real reason why 10.1.2.3 should be part of a class A network and 220.1.2.3 is part of a class C network - it just is. The address space was split up as shown below, and any addresses in these ranges are deemed to be in the appropriate Class. Why does this matter? Well, some software will ask for an IP address but NOT a netmask - and it will infer a netmask from the address. This is OK as long as you are staying within the class system, but if you are subnetting or supernetting, it can cause you a lot of trouble.
Before we start - a quick and very basic recap on IP addressing in general.
Every machine on the net has an address. Addresses are 32 bits. These 32 bits are split into two parts - a network number followed by a host address. The 'host address' part is for a number of machines on one physical network - say a bunch of machines connected with a hub or on a single thin ether wire. The network number represents this group of hosts as a single unit, and routers need to know these network numbers to send data from one net to another.
Just where the network/host split is made is arbitrary. There's no real reason why 10.1.2.3 should be part of a class A network and 220.1.2.3 is part of a class C network - it just is. The address space was split up as shown below, and any addresses in these ranges are deemed to be in the appropriate Class. Why does this matter? Well, some software will ask for an IP address but NOT a netmask - and it will infer a netmask from the address. This is OK as long as you are staying within the class system, but if you are subnetting or supernetting, it can cause you a lot of trouble.
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