understanding ip addresses

Tuesday, July 14, 2009
each IP address consists of a network ID and a host ID. the network ID, also known as the network address, identifies the systems that are located on the same physical network. all computers in the same physical network must have the same network ID, and the network ID must be unique to the internetwork. the host ID, also known as the host address, identifies each TCP/IP host within a network.

IP addresses are logical 32-bit numbers that are broken down into four 8 bit fields known as octets. microsoft TCP/IP supports class A, B and C addresses. the class addresses define which bits are used for network ID and which bits are used for the host ID.

Class A

the first network ID is 1.0.0.0 and the last is 126.0.0.0 , this allows for 126 networks and 16,777,214 hosts per network. the class A adress 127.x.x.x is reserved for loopback testing and interprocess communications on the local computer. for class A addresses, the network ID is laways the first octet in the address and the host ID is the last three octets.

Class B

the first network ID is 128.0.0.0 and the last is 191.255.0.0 , this allows for 16,384 networks and 65,534 hosts per network. for class B addresses the network ID is always the first two octets in the address and host ID is the last two octets.

Class C

the first network ID is 192.0.0.0 and the last is 223.255.255.0 , this allows for 2,097,152 networks and 254 hosts per network. for class C addresses, the network ID is always the first three octets in the address and the host ID is the last octet.

options for configuring a static TCP/IP address

IP address - a logical 32-bit address that identifies a TCP/IP host. each network adpter card in a computer running TCP/IP require a unique IP address, such as 192.168.0.108 , each address has two parts: a network ID, which identifies all hosts on the same physical network, and a host ID which identifies a host on the network. in this example the network ID is 192.168.0 and the host ID is 108.

subnet mask - subnets divide a large network into multiple physical networks connected with routers.a subnet mask blocks out part of the IP address so that TCP/IP can distinguish the network ID from the host ID. when TCP/IP hosts try to communicate, the subnet mask determine whether the destination host is on a local or remote network. to communicate on a local network, computers must have the same subnet mask.

default gateway - the intermediate device on a local network that stores network ID,s of other networks in the enterprise or internet. to communicate with a host on another network, configure an IP address for the default gateway. TCP/IP sends packets for remote networks to the default gateway (if no other route is configured) which then forwards the packets to other gateways until the packet is delivered to a gateway connected to specified destination.

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