Overview of Routing in the Global Internet Today

• The problem of scalability– Each router must know where to send a packet

next.

IP address Next hop (interface #)

128.132.4.123 1

128.125.5.123 2

125.35.124.24 3

27.34.43.43 2

34.39.23.1 3

64.34.56.111 2

72.119.12.34 1

The forwarding table are huge!!!

SubnettingDivide and conquer

128.132.1XX.XXX

72.111.19X.XXX

24.124.123.XXX

128.120.XXX.XXX

A

B

116.24.XXX.XXX

IP address mask #

128.132.0.0 255.255.128.0 2

128.120.0.0 255.255.0.0 1

24.124.123.0 255.255.255.0 3

72.111.19.0 255.255.?.0 3

116.24.0.0 255.255.0.0 3

1

2 3

IP address mask #

128.0.0.0 255.0.0.0 1

24.124.123.0 255.255.255.0 2

72.111.19.0 255.255.?.0 4

116.24.0.0 255.255.0.0 3

A

B

12

34

Must carefully distribute addresses