Transcript IP Address Classes

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
In Group
Accept
Packets to
Multicast Address
Not in Group
Reject
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
Multiple
Packets
Single
Packet
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