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 toMulticast Address

Not in GroupReject

In GroupAccept

In GroupAccept

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

SinglePacket

MultiplePackets

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