Sub netting

Subnetting

Sub-netting is a process of breaking the network into smaller units. These units can be called subnets. Each subnet is a non-physical description(ID) for a physical sub-network.

Benefits of Sub netting

• Reduce network traffic.
• Reduce the size of the routing table.
• Simplified Management: It’s easier to identify and isolate network problems in a group of smaller connected networks than within one gigantic network.
• Optimized network performance: This is a result of reduced network traffic.
• It also increases security of the network and helps contain network traffic to local network segments.

With sub-netting, the number of segments increases, while the number of hosts in each segment reduces. For example, consider a network with an IP address of 192.168. 2.0. With the default subnet mask of 255.255.255.0, you can have only one large network segment with 254 hosts. If you use some bits from the host portion, you can create two, three, or four segments. But as the number of segments increases, the number of hosts in each segment reduces.

Implementing Sub netting

Before implementation, we can determine some requirement and plans to best implement your subnet scheme.

• Determine the number of required network IDs
       -One for each subnet
       -One for each wide-area network connection.
• Determine the number of required host IDs per subnet
       -One for each TCP/IP host
       -One for each router interface
• Define one subnet mask based on requirements.
• Define a unique subnet ID for each physical segment based on the subnet mask.
• Define valid host IDs for each subnet based on the subnet ID.

Subnet Mask

Subnet mask is a 4 byte (32 bits) number used to identify the sub-network ID and the host ID from an IP address. Every class of the IP address uses the different range of the sub-network. Subnet mask allow the IP based networks to be divided into the sub network, i.e, 255.255.255.0, 255.255.170.0. Table shows the default subnet mask of class A,B, and C.

IP Addressing

IP Addressing
An IP address is a unique address used to identify a computer or a host on the network. This address is made up of 32-bit numbers written in dotted decimal notation in the w.x.y.z format. Each eight bits are known as an octet or a byte. A part of the IP address is known as the network address, or network ID, and the rest of it is known as the host address, or host ID. These parts are based on the class of IP addresses used on the network. All computers on a particular network must have the same number as the network address, while the host address must be unique on the entire network. A second address, the subnet mask, is used to help identify the part of the network where the host is located.

IP addresses are assigned and controlled by an organization called Internet Assigned Numbers Authority (IANA). There are two current versions of IP addressing: IPv4 and IPv6.

Example: 140.179.220.200

Binary form:
140                  179              220                 200
10001100    10110011       11011100      11001000

IP Terminology:
Bit: A bit is a one digit, either a 1 or 0.
Byte: A byte is a 7 or 8 bits. Today, we can always assumed a byte is 8 bits.
Octet: An octet; made up of 8 bits.

IPv4 addresses

IPv4 addresses are classified into classes A, B, C, D, and E. Only addresses from the classes A, B, and C are assigned to organizations and are known as class-full IP addresses. The first byte of an IP address identifies the class of IP addresses used in the network. For example, a host with an IP address of 92.137.0.10 is using a class A IP address. A host with an IP address of 192.170.200.10 is using a class C IP address. The IP addresses in the A, B, and C classes are available for public companies and can be assigned by an ISP. The class D and E addresses are reserved for special usage.

IP Address Classes
IP addresses can be categorized into different types of classes. These are:
     • Class A
     • Class B
     • Class C
     • Class D
     • Class E

(i) Class A:
Class A addresses are designed for networks with a large number of hosts. The high-order bit is set to 0. The first 8 bits (the first octet) are defined as the network ID; the last 24 bits(the last three octets) are defined as the host ID. Figure illustrates the class A address.



Range is: 1-126
Maximum number of networks: 126(27-2).
Maximum nodes per networks: 16,777,214(224-2).

(ii) Class B:
Class B addresses are designed for moderate-sized networks with a moderate number of hosts. The two high-order bits are set to 10. The first 16 bits (the first two octets) are defined as the network ID; the last 16 bits (the last two octets) are defined as the host ID. Figure illustrates the class B address.

Range is: 128-191
Maximum number of networks: 16384 (214).
Maximum nodes per network: 65534(216-2).

(iii) Class C:
Class C addresses are designed for small networks with a small number of hosts. The three high-order bits are set to 110. The first 24 bits (the first three octets) are defined as the network ID; the last 8 bits (the last three octets) are defined as the host ID. Figure illustrates the class C address.

Range is : 192-223
Maximum number of networks: 2097152(221).
Maximum nodes per network: 254(28-2).

(iv) Class D
Class D addresses are for IP multicast addresses. The four high-order bits are set to binary 1110. The next 28 bits are used for individual IP multicast addresses. The Microsoft Windows Server 2003 family supports class D addresses for IP multicast traffic.
Range is : 224-239

(v) Class E

Class E addresses are experimental addresses reserved for future use. The five high-order bits in a class E address are set to 11110. The Windows Server 2003 family does not support the use of class E addresses.
Range is : 240-255.

Table : IP Address Classes

Network Address (ID)
A network address uniquely identifies a network. All the host in a single network will have the same network address. For example, in the IP address 192.9.205.21, the network ID is 192.9.205. A router analyses only the network ID portion of an address for datagram forwarding.

Node (Host) Address/ID
A node ID uniquely identify a host in a network. Two hosts in two different networks can have the same host ID. For example, in the IP address 192.9.250.21, the host ID is 21.

Private IP Addresses
An IP address is considered private if the IP number falls within one of the IP address ranges reserved for private uses by Internet Standards groups. Private IP addresses (or unregistered IP addresses), on the other hand, are used when an organization’s computer network is private. In other words, it is not connected to the Internet or if it is, it is located behind a proxy server or a firewall. Access to private networks is usually restricted to users inside the organization. The Internet Assigned Numbers Authority (IANA) has set aside a range of IP addresses in each of A, B, and C address classes that can be used by private organizations for their internal IP addressing. These addresses are listed in Table .

Private IP addresses are typically used on local networks including home, school and business LANs, including Airport and Hotels.


Devices with private IP addresses cannot connect directly to the Internet like wise, computers outside the LAN cannot directly to device with a Private IP. But if you want to access the internet with this ip address you must have to use proxy server or NAT server.

Public IP Address
Public IP addresses (or registered IP addresses) are those addresses of those networks that are accessible from outside the organization. For example, if any host is connected to a network, it is using a public IP address. If an organization needs to connect its network to the Internet, it will need to obtain a public IP address from its Internet Service Provider. Typically, web servers, email servers, DNS servers, FTP servers, and VPN servers are connected directly to the Internet and use public IP addresses.

Broadcast Address
In computer networking, a broadcast address is a network address that allows information to be sent to all nodes on a network, rather than to a specific network host. In other word’s A special type of networking address that is reserved for sending messages to all machines on a given network segment.