Route Summarization in OSPF

Route Summarization between two areas

Router 2 IP addressing: 

interface Loopback1

 ip address 22.22.22.22 255.255.255.255

!

interface Loopback23

 ip address 23.23.23.23 255.255.255.255

!

interface Loopback24

 ip address 24.24.24.24 255.255.255.255

!

interface Loopback25

 ip address 25.25.25.25 255.255.255.255

!

interface fastethernet 0/0

 ip address 3.3.3.1 255.255.255.0

!

R2(config)#router ospf 2

R2(config-router)#network 22.0.0.0 0.255.255.255 area 1

R2(config-router)#network 23.0.0.0 0.255.255.255 area 1

R2(config-router)#network 24.0.0.0 0.255.255.255 area 1

R2(config-router)#network 25.0.0.0 0.255.255.255 area 1

R2(config-router)#network 3.3.3.0 0.0.0.255 area 0

R1(config)#router ospf 2

R1(config-router)#network 3.3.3.0 0.0.0.255 area 0

R1#sh ip route ospf

     23.0.0.0/32 is subnetted, 1 subnets

O IA    23.23.23.23 [110/2] via 3.3.3.1, 00:00:02, FastEthernet0/1

     22.0.0.0/32 is subnetted, 1 subnets

O IA    22.22.22.22 [110/2] via 3.3.3.1, 00:00:02, FastEthernet0/1

     25.0.0.0/32 is subnetted, 1 subnets

O IA    25.25.25.25 [110/2] via 3.3.3.1, 00:00:02, FastEthernet0/1

     24.0.0.0/32 is subnetted, 1 subnets

O IA    24.24.24.24 [110/2] via 3.3.3.1, 00:00:02, FastEthernet0/1

Finding Summarized Route

00010110.00000000.00000000.00000000 22.0.0.0

00010111.00000000.00000000.00000000 23.0.0.0

00011000.00000000.00000000.00000000 24.0.0.0

00011001.00000000.00000000.00000000 25.0.0.0

00010000.00000000.00000000.00000000 16.0.0.0

11110000.00000000.00000000.00000000 240.0.0.0

R2(config)#router ospf 2

R2(config-router)#area 1 range 16.0.0.0 240.0.0.0

R1#sh ip route ospf

O IA 16.0.0.0/4 [110/2] via 3.3.3.1, 00:00:04, FastEthernet0/1