IP Address Classes

1
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)

2
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

3
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

4
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

5
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

6
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

In Group Accept
Packets to Multicast Address
Not in Group Reject
In Group Accept
7
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

8
Why Multicasting

• Do not need to send an IP packet to each host
• Routers split when needed
• Reduces traffic

Multiple Packets
Single Packet
9
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