Net9: IP Address 授課教師：雲林科技大學 張慶龍 老師

IP Address IP denoted - in the form each number represents, in decimal, 1 byte of the 4-byte IP address. Why are IP addresses necessary? –Easy to find the destination station –IP addresses are hierarchical addresses Every IP address has two parts. –network number (provided by InterNIC) –host number (provided by local administrator) –Where to find the IP address International Network Information Center, or InterNIC –There are five classes of Network (Five type IP) only three of these are used commercially. These are the class "A," "B," and "C" networks the class “D” is reserved for multicast the class “E” is reserved for experiment/research

What IP addresses are reserved for the Networks? – Network address : all host address are set to zero – Broadcase address : all host address are set to one Question: What would the network/broadcase address be for devices such as the one with an IP address of ? In order to provide extra flexibility for the network administrator, often networks, particularly large networks, are divided into smaller networks called subnetworks. Most of the time subnetworks are simply referred to as subnets. Who assigns subnet addresses? – this is done by the network administrator

How are subnet addresses created? – a network administrator "borrows" bits from the host field and designates them as the subnet field. The function of a subnet mask is to tell devices which part of an address is the network number including the subnet, and which part is the host.

How many bits can be borrowed from the host number in class "B" and class "C" networks to create subnets? – only two octets in the host field of a class "B" network, up to fourteen bits can be borrowed to create subnetworks. A class "C" network has only one octet in the host field. only up to six bits can be borrowed Subnet binary bit range of range of host of subnet host field field decimal First Subnet thru thru.31 Second Subnet thru thru.63 Third Subnet thru thru.95 Fourth Subnet thru thru.127 Fifth Subnet thru thru.159 Sixth Subnet thru thru.191 Seventh Subnet thru thru.223 Eighth Subnet thru thru.255

CIDR, classless interdomain routing The mask is merely a number, called the prefix – Specify the length in bits of the network portion of the address – EX: /22, where /22 indicating the prefix – Ex: /26, which can support up to = 62 hosts Longest prefix match for routing table search