IPv4 ADDRESSING and PACKET STRUCTURE

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: 66.102.7.104 (Google) A host can send a packet to an IP address and it will be delivered to the correct destination.

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 - 0: reserved for network address - 255: reserved for broadcast address

Network Address Host A B Network Address Host C Network Address Host

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

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 174.148.0.0 would have a broadcast address of 174.148.255.255

Network Address: is formed by replacing all host bytes with 0. Example: Class B IP address of 174.148.10.5, has network address of 174.148.0.0 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 = 255.0.0.0, Class B = 255.255.0.0

5 Different Classes of IP Address CLASS A 1.0.0.0 to 127.255.255.255 CLASS B 128.0.0.0 to 191.255.255.255 CLASS C 192.0.0.0 to 223.255.255.255 CLASS D 224.0.0.0 to 239.255.255.255 CLASS E 240.0.0.0 to 255.255.255.255

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 10.0.0.0 255.0.0.0 126 16,646,144 CLASS B 172.16.0.0 to 172.31.0.0 255.255.0.0 16,383 65,024 CLASS C 192.168.0.0 to 192.168.255.255 255.255.255.0 2,097,151 254 LOOPBACK (localhost) 127.0.0.0 to 127.0.0.7 -