1. IPv4 ADDRESSING and PACKET STRUCTURE

2. IPv4
Internet Protocol addressing version 4 (IPv4) is the basis of Internet.
Every connected host has a four octet address expressed in decimal:
AAA.BBB.CCC.DDD
For example: (Google)
A host can send a packet to an IP address and it will be delivered to the correct destination.

3. CLASSFUL ADDRESSING
Under IPv4 addressing scheme (classful addressing), the class of the network may be A, B or C. The class effects how the four number IP address is intrepreted. For all classes, the last byte is limited between: 1 – 254
: reserved for network address
- 255: reserved for broadcast address

4. Network
Address
Host A B
Network
Address
Host C
Network
Address
Host

5. CLASS A (large network): the first byte identifies the network and the last 3 bytes represent an address range for hosts on the network.
Byte 1: 1 – 126
Byte 2 and 3: 0 – 255
No. of hosts (max): 16,646,144
CLASS B (medium network): the first two bytes identify the network and the last 2 bytes represent an address for hosts on the network.
Byte 1: 128 – 191
No. of hosts (max): 65,024
CLASS C (small network): the first three bytes identify network and the last byte represent an address for hosts on the network.
Byte 1: 192 – 223
No. of hosts (max): 254 hosts
CLASS D: Byte 1: 224 – 239
CLASS E: Byte 1: 240 – 255

6. Broadcast Address: broadcast address is intended to go to every host on the network.
(host address bytes are replaced with 255 (all ones)
Example: Class B network with a network address of would have a broadcast address of

7. Network Address: is formed by replacing all host bytes with 0.
Example: Class B IP address of , has network address of
Network Mask (netmask): a host must know if a received packet relates to the network to which the host is a member. Membership of a network is determined using netmask defined on every network host.
netmask = all network bits set to 1, all hosts bits
set to 0
Example: Class A = , Class B =

8. 5 Different Classes of IP Address
CLASS A to
CLASS B to
CLASS C to
CLASS D to
CLASS E to

9. PRIVATE IP ADDRESS (are not used anywhere on public internet, reserved for private LANs)
Network Class
Network Numbers
Network Mask
No. of Networks
No. of Hosts per Network
CLASS A
126
16,646,144
CLASS B to
16,383
65,024
CLASS C to
2,097,151
254
LOOPBACK (localhost) to -