6.     Supernatting VLSM-CIDR

Classless Inter-Domain Routing CIDR has been discussed since 1993.

It is a method of assigning IP addresses that improves the efficiency of address distribution and replaces the previous system 

based on Class A, Class B and Class C networks.

In the classful network design, If an organization needed more than 254 host machines, it would be switched into
Class B. However, this could potentially waste over 60,000 hosts if the business didn't need to use them,
thus unnecessarily decreasing the availability of IPv4 addresses. CIDR was introduced to fix this problem.
CIDR allows you to go beyond subnetting->Supernetting. The latter makes it possible to resolve the problem of
assigning IP addresses.
CIDR is based on variable-length subnet masking (VLSM), which enables network engineers to divide an IP address
space into a hierarchy of subnets of different sizes. 
CIDR classless inter-domain routing combined with NAT allow to the IP addresses to resist.

Supernetting also allows administrators to represent multiple networks in a single row in the routing table using a single mask. This makes it possible to reduce the size of the routing tables. Indeed, the ability to synthesize multiple subnets into an address and a supernet mask significantly reduces the sizes of routing tables.

 

Example 1

An Internet Service Provider (ISP) to whom we assign the 94.20.0.0/16 network can assign subnetworks to its customers:

    94.20.1.0/24 to a first company

    94.20.2.0/24 to a second company ...etc.

    94.20.0.0/16 is published in the routing table to represent all networks.

 

Example 2

172.16.12.0/24  ----> 10101100.00010000.000011 00.00000000

172.16.13.0/24 ----> 10101100.00010000.000011 01.00000000

172.16.14.0/24 ----> 10101100.00010000.000011 10.00000000

172.16.15.0/24 ----> 10101100.00010000.000011 11.00000000

The network address that synthesizes these 4 entries.

address 172.16.12.0 ----> 10101100.00010000.000011 00.00000000

Mask: 255.255.252.0 ---> 11111111.11111111.11111100.00000000

VLSM is useful to ISPs and also network administrators.

Example3

 

Modifié le: mardi 4 juin 2024, 11:18