Implementing OSPF Stub Areas on Cisco Routers
- April 7, 2024
- Posted by: Lyfey Technologies
- Categories: Cisco, Networking
An OSPF Stub Area helps in simplifying routing in larger OSPF networks and makes routing more efficient. Routers in a stub area do not flood external (Type 5) LSAs and Type 3 LSAs (depending on the type of stub area).
Routers within a stub area only know internal routes, making routing tables smaller and more efficient. SPF calculation is simpler and faster convergence is possible.
Configuration Steps
Step 1: Configure IP addresses on interfaces on all routers.
*****************************R1
enable
configure terminal
!
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface FastEthernet0/0
ip address 10.10.10.0 255.255.255.254
no shutdown
!
interface FastEthernet0/1
ip address 10.10.10.2 255.255.255.254
no shutdown
!
interface FastEthernet1/0
ip address 30.30.30.0 255.255.255.254
no shutdown
!*****************************R2
enable
configure terminal
!
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface FastEthernet0/0
ip address 20.20.20.2 255.255.255.254
no shutdown
!
interface FastEthernet0/1
ip address 20.20.20.0 255.255.255.254
no shutdown
!
interface FastEthernet1/0
ip address 30.30.30.1 255.255.255.254
no shutdown
!*****************************R3
enable
configure terminal
!
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface FastEthernet0/0
ip address 10.10.10.1 255.255.255.254
no shutdown
!
interface FastEthernet0/1
ip address 10.10.10.4 255.255.255.254
no shutdown
!*****************************R4
enable
configure terminal
!
interface Loopback0
ip address 4.4.4.4 255.255.255.255
!
interface FastEthernet0/0
ip address 10.10.10.3 255.255.255.254
no shutdown
!
interface FastEthernet0/1
ip address 10.10.10.5 255.255.255.254
no shutdown
!*****************************R5
enable
configure terminal
!
interface Loopback0
ip address 5.5.5.5 255.255.255.255
!
interface FastEthernet0/0
ip address 20.20.20.3 255.255.255.254
no shutdown
!
interface FastEthernet0/1
ip address 20.20.20.4 255.255.255.254
no shutdown
!*****************************R6
enable
configure terminal
!
interface Loopback0
ip address 6.6.6.6 255.255.255.255
!
interface FastEthernet0/0
ip address 20.20.20.1 255.255.255.254
no shutdown
!
interface FastEthernet0/1
ip address 20.20.20.5 255.255.255.254
no shutdown
!Step 2: Configure OSPF on all the routers.
******************************R1
router ospf 10
router-id 1.1.1.1
log-adjacency-changes
network 1.1.1.1 0.0.0.0 area 0
network 10.10.10.0 0.0.0.1 area 2
network 10.10.10.2 0.0.0.1 area 2
network 30.30.30.0 0.0.0.1 area 0
!******************************R2
router ospf 10
router-id 2.2.2.2
log-adjacency-changes
network 2.2.2.2 0.0.0.0 area 0
network 20.20.20.0 0.0.0.1 area 2
network 20.20.20.2 0.0.0.1 area 2
network 30.30.30.0 0.0.0.1 area 0
!******************************R3
router ospf 10
router-id 3.3.3.3
log-adjacency-changes
network 3.3.3.3 0.0.0.0 area 0
network 10.10.10.0 0.0.0.1 area 2
network 10.10.10.4 0.0.0.1 area 2
!******************************R4
router ospf 10
router-id 4.4.4.4
log-adjacency-changes
network 4.4.4.4 0.0.0.0 area 0
network 10.10.10.2 0.0.0.1 area 2
network 10.10.10.4 0.0.0.1 area 2
!******************************R5
router ospf 10
router-id 5.5.5.5
log-adjacency-changes
network 5.5.5.5 0.0.0.0 area 0
network 20.20.20.2 0.0.0.1 area 1
network 20.20.20.4 0.0.0.1 area 1
!******************************R6
router ospf 10
router-id 6.6.6.6
log-adjacency-changes
network 6.6.6.6 0.0.0.0 area 0
network 20.20.20.0 0.0.0.1 area 1
network 20.20.20.4 0.0.0.1 area 1
!Step 3: Verify OSPF adjacent status on all routers
Step 4: Create Loopback 100 on R3 and redistribute it into OSPF as an external route.
******************************R3
!
interface Loopback100
ip address 100.100.100.100 255.255.255.255
!
ip prefix-list DISTRIBUTE_DIRECT seq 10 permit 100.100.100.100/32
!
route-map DISTRIBUTE_DIRECT permit 10
match ip address prefix-list DISTRIBUTE_DIRECT
!
router ospf 10
redistribute connected subnets route-map DISTRIBUTE_DIRECT
!Step 5: Verify LSDB on all routers. As shown below, R3 and R5 have received Type 5 LSAs in their LSDB.
Step 6: Configure Area 1 as Stub area. Run stub command on R2, R5 and R6.
Note: The stub command must be run on all routers in Area 1 for the area to be stub area. The adajaceny relationship will go down if stub is configured only on one of the adjacent routers.
***************************R2,R5,R6
!
router ospf 10
area 1 stub
!Step 7: Verify the routing table of R5 and R6
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