Configure external OSPF route summary on ASBR

 

 

An external LSA (Class 5 LSA) is used to advertise each external route that is redistributed from other protocols (such as OSPF) to OSPF. In ASBR, five types of LSA can be summarized and injected into the OSPF domain.

R1 Configuration:

Interface Loopback1

Ip address 1.1.1.1 255.255.255.255

!

Interface Loopback2

Ip address 1.1.2.1 255.255.255.255

!

Interface Loopback3

Ip address 1.1.3.1 255.255.255.255

!

Interface Loopback4

Ip address 1.1.4.1 255.255.255.255

!

Interface Serial1/1

Ip address 10.0.1.1 255.255.255.0

Serial restart-delay 0

!

Router ospf 1

Log-adjacency-changes

Network 1.1.1.0 0.0.0.255 area 0

Network 1.1.2.0 0.0.0.255 area 0

Network 1.1.3.0 0.0.0.255 area 0

Network 1.1.4.0 0.0.0.255 area 0

Network 10.0.1.0 0.0.0.255 area 0

!

 

R2 Configuration:

Interface Serial1/0

Ip address 10.0.1.2 255.255.255.0

Serial restart-delay 0

!

Interface Serial1/1

Ip address 10.0.2.1 255.255.255.0

Serial restart-delay 0

!

Router VPN 1

Network 10.0.2.0 0.0.0.255

Auto-summary

!

Router ospf 1

Redistribute Fig 1 subnets // route the route of the OSPF network to the OSPF

Network 10.0.1.0 0.0.0.255 area 0

!

 

R3 Configuration:

Interface Loopback1

Ip address 3.3.3.3 255.255.255.255

!

Interface Loopback2

Ip address 3.3.2.3 255.255.255.0

!

Interface Loopback3

Ip address 3.3.1.3 255.255.255.0

!

Interface Loopback4

Ip address 3.3.4.3 255.255.255.0

!

Interface Serial1/0

Ip address 10.0.2.2 255.255.255.0

Serial restart-delay 0

!

Router VPN 1

Network 3.3.1.0 0.0.0.255

Network 3.3.2.0 0.0.0.255

Network 3.3.3.0 0.0.0.255

Network 3.3.4.0 0.0.0.255

Network 10.0.2.0 0.0.0.255

No auto-summary

!

Ip route 0.0.0.0 0.0.0.0 10.0.2.1 // create a default route

 

After the preceding configuration is complete, view the R1 route table:

 

R1 # show ip route

Codes: C-connected, S-static, R-RIP, M-mobile, B-BGP

D-OSPF, EX-VPN external, O-OSPF, IA-OSPF inter area

N1-ospf nssa external type 1, N2-ospf nssa external type 2

E1-OSPF external type 1, E2-OSPF external type 2

I-IS, su-IS summary, L1-IS-level-1, L2-IS level-2

Ia-IS inter area, *-candidate default, U-per-user static route

O-ODR, P-periodic downloaded static route

 

Gateway of last resort is not set

 

1.0.0.0/32 is subnetted, 4 subnets

C 1.1.1.1 is directly connected, Loopback1

C 1.1.3.1 is directly connected, Loopback3

C 1.1.2.1 is directly connected, Loopback2

C 1.1.4.1 is directly connected, Loopback4

3.0.0.0/8 is variably subnetted, 4 subnets, 2 masks

O E2 3.3.3.3/32 [110/20] via 10.0.1.2, 00:00:10, Serial1/1

O E2 3.3.1.0/24 [110/20] via 10.0.1.2, 00:00:10, Serial1/1

O E2 3.3.2.0/24 [110/20] via 10.0.1.2, 00:00:10, Serial1/1

O E2 3.3.4.0/24 [110/20] via 10.0.1.2, 00:00:10, Serial1/1

10.0.0.0/24 is subnetted, 2 subnets

O E2 10.0.2.0 [110/20] via 10.0.1.2, 00:29:44, Serial1/1

C 10.0.1.0 is directly connected, Serial1/1

 

The detailed route entries in the network are displayed. 3.3.1.0-3.3.4.0 is a continuous CIDR block. We can route the route entry 3.3.3.0.0/21 to R1, which will reduce the number of Route entries in R1.

 

OSPF route summary on R2 (ASBR:

 

R2 # conf ter

R2 (config) # router ospf 1

R2 (config-router) # summary-address 3.3.0.0 255.255.248.0

 

View the R1 route table again:

 

R1 # show ip route

Codes: C-connected, S-static, R-RIP, M-mobile, B-BGP

D-OSPF, EX-VPN external, O-OSPF, IA-OSPF inter area

N1-ospf nssa external type 1, N2-ospf nssa external type 2

E1-OSPF external type 1, E2-OSPF external type 2

I-IS, su-IS summary, L1-IS-level-1, L2-IS level-2

Ia-IS inter area, *-candidate default, U-per-user static route

O-ODR, P-periodic downloaded static route

 

Gateway of last resort is not set

 

1.0.0.0/32 is subnetted, 4 subnets

C 1.1.1.1 is directly connected, Loopback1

C 1.1.3.1 is directly connected, Loopback3

C 1.1.2.1 is directly connected, Loopback2

C 1.1.4.1 is directly connected, Loopback4

3.0.0.0/21 is subnetted, 1 subnets

O E2 3.3.0.0 [110/20] via 10.0.1.2, 00:02:42, Serial1/1

10.0.0.0/24 is subnetted, 2 subnets

O E2 10.0.2.0 [110/20] via 10.0.1.2, 00:27:40, Serial1/1

C 10.0.1.0 is directly connected, Serial1/1

From: renzhongming's BLOG