6. 6
Classful Addressing
121. 30.112.24
011101001. 00011110.01110000.00011000
Network ID Host ID
Class Pattern 1st
Octet #addresses/net
A x.x.x.x 1 â 127 2563
B x.X.x.x 128- 191 2562
C x.X.X.x 192 - 223 256
7. 7
Classless Addressing
⢠Allows for breaking up of a classful address range.
⢠Helps conserve IP addresses.
⢠Important for network segmentation
9. 9
1111
xxxx xxxx.xxxxxxxx.xxxxxxxx
Subnet Mask
AND
xxxxxxxx.IP Address
1111 1111. 0000.00000000.00000000Subnet Mask
xxxxxxxx. xxxx 0000.00000000.00000000Subnet ID
⢠CIDR Notation (Classless Inter-Domain Routing)
- Specifies the length of the network portion with a number after a slash (/).
â˘Example Address: 192.168.129.10/18
The subnet mask equivalent to this CIDR notation is 255.255.192.0
The subnet ID is calculated as:
192.168.129.10 AND 255.255.192.0 = 192.168.128.0
10. 10
VLSM (Variable Length Subnet Masks)
⢠Custom subnet masks generate subnets that are all of the
same size.
â Note: Subnet masks associated with the A, B and C classes are
called default subnet masks.
⢠This limitation still results in the wastage of addresses.
⢠Example: A class C network can be divided into 4
subnets each accommodating 62 hosts. On a subnet that
requires only 2 hosts, 60 addresses will be wasted.
⢠VLSM prevents this by allowing recursive subnetting.
11. 11
VLSM
Example: Given the IP address of 196.220.10.0/24, propose an addressing
scheme to accommodate three subnets with 2, 30 and 100 hosts.
Solution: The host portion is initially 8 bits long which supports 254 hosts.
Order the subnets in a decreasing number of hosts: Net1: 100, Net2: 30, Net3:
2
Net1: 100 hosts ď Requires 128 = 27
addresses ď borrow 1 bit ď 2 subnets
are available, new CIDR prefix = /25 , BS= 128
196.220.10. x | 000 0000
Subnet ID#1: x=0 ď 196.220.10.0/25 (196.220.10.1 to 196.220.10.127)
Assign this subnet to Net1.
Subnet ID#2: x=1 ď 196.220.10.128/25 (196.220.10.127 to 196.220.10.255)
Break this down further for other subnets.
13. 13
Summary
⢠IP addressing techniques are used to
segment a given address range.
⢠Segmentation results in IP address
conservation, security and better
performance.