IP Address Classes How large is the network part in an IP address? Today we use network masks to tell Originally, IP had address classes with fixed numbers of bits in the network part –Class A: 8 bits (24 bits in local part) –Class B: 16 bits (16 bits in local part) –Class C: 24 bits (8 bits in local part)

Class A IP Address IP address begins with 0 7 remaining bits in network part –Only 128 possible Class A networks 24 bits in local part –Over 16 million hosts per Class A network! All Class A network parts are assigned or reserved

Class B IP Address IP address begins with 10 (1st zero in 2nd position) 14 remaining bits in network part –Over 16,000 possible Class B networks 16 bits in local part –Over 65,000 possible hosts A good trade-off between number of networks and hosts per network Most have been assigned

Class C IP Address IP address begins with 110 (1st zero in 3d position) 21 more bits in network part –Over 2 million possible Class C networks! 8 bits in local part –Only 256 possible hosts per Class C network! Unpopular, because large firms must have several

Class D IP Address IP address begins with 1110 Used for multicasting, not defining networks –Sending message to group of hosts –Not just to one (unicasting) –Not ALL hosts (broadcasting) –Say to send a videoconference stream to a group of receivers

Class D IP Address All hosts in a multicast group listen for this multicast address as well as for their specific own host IP address Packets to Multicast Address Not in Group Reject In Group Accept In Group Accept

Multicasting Traditionally, unicasting and broadcasting –Unicasting: send to one host –Broadcasting: send to ALL hosts Multicasting –Send to SOME hosts –500 stations viewing a video course –50 computers getting software upgrades –Standards exist and are improving –Not widely implemented yet

Why Multicasting Do not need to send an IP packet to each host –Routers split when needed –Reduces traffic Single Packet Multiple Packets

Mobile IP IP addresses are associated with fixed physical locations Mobile IP is needed for notebooks, other portable equipment Computer still gets a permanent IP address When travels, also gets a temporary IP address at its location This is linked dynamically to its permanent IP address