18-08-2012, 03:04 PM
Subnetting and Supernetting
1Subnetting.ppt (Size: 1.11 MB / Downloads: 67)
Concepts Background
The increasing number of host connected to the internet
Restrictions on the network size
In subnetting, a network is divided into smaller subnetworks with each subnet having its own subnet address
In supernetting, a organization can combine several class C to create a large range of addresses. In other word, several networks are combined to create a supernetwork
Subnetting
IP address (32 bits) netid and hostid
Means: there is a sense of hierarchy in IP addressing.
To reach a host, we must first reach the network using netid, then using hostid to reach the host
Generall: class A, B, C two levels of hierarchy
Sometimes two levels is not enough
For example, imagine an organization with a class B address. The organization has two levels hierarchical addressing, but it cannot have more than one physiscal network
The host cannot be grouped, and all of the host has the same level
Solution subnetting
Masking
A process that extracts the address of the physical network from IP address
Can be done whether we have subnet or not.
Not have subnet: masking extract the network address from an IP address.
Have subnet: masking extract the subnet address from IP address.
In masking:
We perform math. operation on a 32-bits IP add. at the bit level using another 32-bit number called mask
The bits in the mask are related to the corresponding IP add.
Part of masking containing 1s defines netid or combination of netid and subnetid
Part of making containing 0s defines hostid
To get the network and subnet address, we must apply the bit-wise-and operation on IP address and the mask
Supernetting
Depend on the need of an organization
One or more classes c can be jointed to make one supernetwork
Example: an organization that needs 1000 address can be granted four class c addresses. The organization can then use these address in one supernetwork, in four network, or in more then four networks.
Supernet Mask
Can be assigned to a block of class C network address, if the number of net. Address is a power of two
Default mask for a class C address 255.255.255.0
If some of the 1s are changed to 0s, we can have a mask for a group of class C
Supernet mask is the reverseof the subnet mask