RECOMMENDED Week 3
Powerpoint presentaton for Module 2 - View Online or Download
Networking Media
Extra Info - IP Numbers
Every node on a TCP/IP network is identified by a unique IP address. This address is used to identify a host on a network; it also specifies routing information on the network. The IP address identifies a computer 32-bit address that is unique accross a TCP/IP network. An address is usually represented in dotted decimal notation, which depicts each octet (eight bits, or one byte) of an IP address as its decimal value and separates each octet with a period. The IP address of NTU looks like this:
138.80.128.1
It is important to note that since an IP address identifies a node on a particular network, each node on the network must be assigned a unique IP address valid for its particular network. Therefore if a machine was assigned an IP address in the 138.80.128 subnet and is subsequently moved into the 138.80.67 subnet, a different IP address must be assigned.
Network ID and Host ID
The IP address contains two pieces of information: the network ID and the host ID for the individual computer.
The network ID identifies a group of computers and other devices that are all located on the same logical network. The host ID identifies an individual computer within a particular network ID.
IP Address Classes
The internet community has defined address classes to accommodate networks of varying sizes. Each network class can be discerned from the first octet of its IP address. The table below shows the relationship between the first octet of a given address and its network ID and host ID fields. It also identifies the total number of network IDs and hosts IDs for each address class in the internet addressing scheme. In the table a,b,c.b is used to designate the bytes of the IP address.
IP Address Classes
| Class | a values | Network ID | Host ID | Available Networks | Available hosts/nets> |
|---|---|---|---|---|---|
| A | 1 - 126 | a | b.c.d | 126 | 16,777,214 |
| B | 128 - 191 | a.b | c.d | 16,384 | 65,534 |
| C | 192 - 223 | a.b.c | d | 2,097,151 | 254 |
Note that the network address 127 is reserved for loopback testing and interprocess communication on the local computer. Adresses 224 and above are reserved for special protocols and cannot be used as host adresses.
Subnet Masks
Subnet masks are 32-bit values that allow the recipient of packets to distinguish the network ID portion of the IP address from the host ID. Like an IP address, the value of a subnet mask is frequently represented in dotted decimal notation. Subnet masks are determined by assigning binary 1's to bits that belong to the host ID. Once the bits are in place, the 32-bit value is converted to dotted decimal notation, as shown in the table below.
Default Subnet Masks for Standard IP Classes
| Address Class | Bits for Subnet Mask | Subnet Mask |
|---|---|---|
| Class A | 11111111 00000000 00000000 00000000 | 255.0.0.0 |
| Class B | 11111111 11111111 00000000 00000000 | 255.255.0.0 |
| Class C | 11111111 11111111 11111111 00000000 | 255.255.255.0 |
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