Hello Friends,Hope you are enjoying my blog and its helping you out in few weird situations.
Lets talk about a weird OSPF scenario that I came across few days back.
I was just doing some of my own designed ospf scenarios when I saw this issue occurring.
Lets talk about the issue now. In my scenario (which is mentioned in above diagram); I established a virtual-link between R2 & R3 to get R4's routes to area 0 as Area 2 was not directly connected to area 0. After that I setup some loop back interfaces on R4 and advertised them in area 2. I also configured ospf network type point-to-point for these loopback interfaces (I hope you got the reason why I changed the network type on loopback interfaces). After that I summarized these networks using area 2 range command on R3 and summarized these loopback networks into one summary route.
Upto this point things were working fine as per my expectations. After that I thought lets do one more summarization :-)
So I created some more loopback interfaces on R3 this time and did the same steps which I performed on R4 earlier ( but advertised loopback interfaces in area 1). But this time even after issuing area 1 range command on R2 you know what I saw in R1 routing table ? :-O
I saw on R1 that It's not only getting summarized route for R3 loopback addresses but also getting loopback network addresses of R3's loopback interfaces with their correct mask and subnets. Means I got summary route as well as normal prefix subnet routes for same addresses in R1's routing table.
e.g.
R1# sh ip rou ospf
2.0.0.0/30 is subnetted, 1 subnets
O IA 2.2.2.0 [110/128] via 1.1.1.2, 00:00:00, Serial0/0
3.0.0.0/30 is subnetted, 1 subnets
O IA 3.3.3.0 [110/192] via 1.1.1.2, 00:00:00, Serial0/0
O IA 192.168.8.0/24 [110/129] via 1.1.1.2, 00:00:00, Serial0/0 ---> Route with accurate prefix (from R3)
O IA 192.168.9.0/24 [110/129] via 1.1.1.2, 00:00:00, Serial0/0 ---> Route with accurate prefix (from R3)
O IA 20.0.0.0/8 [110/74] via 1.1.1.2, 00:00:00, Serial0/0
O IA 192.168.10.0/24 [110/129] via 1.1.1.2, 00:00:00, Serial0/0 ---> Route with accurate prefix (from R3)
172.16.0.0/22 is subnetted, 1 subnets
O IA 172.16.8.0 [110/193] via 1.1.1.2, 00:00:00, Serial0/0
O IA 192.168.11.0/24 [110/129] via 1.1.1.2, 00:00:00, Serial0/0 ---> Route with accurate prefix (from R3)
O IA 40.0.0.0/8 [110/202] via 1.1.1.2, 00:00:00, Serial0/0
O IA 30.0.0.0/8 [110/138] via 1.1.1.2, 00:00:00, Serial0/0
O IA 192.168.8.0/22 [110/129] via 1.1.1.2, 00:00:00, Serial0/0 ---> Huh..and summary route as well :-)
I beat my head against the wall for quite some time and finally I tried one thing which worked for me...yyoohhhooo :-)
I configured the same area 1 range command on R3 as well and summarization issue got fixed.
R1#sh ip route ospf
2.0.0.0/30 is subnetted, 1 subnets
O IA 2.2.2.0 [110/128] via 1.1.1.2, 00:00:10, Serial0/0
3.0.0.0/30 is subnetted, 1 subnets
O IA 3.3.3.0 [110/192] via 1.1.1.2, 00:00:10, Serial0/0
O IA 20.0.0.0/8 [110/74] via 1.1.1.2, 00:00:10, Serial0/0
172.16.0.0/22 is subnetted, 1 subnets
O IA 172.16.8.0 [110/193] via 1.1.1.2, 00:00:10, Serial0/0
O IA 40.0.0.0/8 [110/202] via 1.1.1.2, 00:00:10, Serial0/0
O IA 30.0.0.0/8 [110/138] via 1.1.1.2, 00:00:10, Serial0/0
O IA 192.168.8.0/22 [110/129] via 1.1.1.2, 00:00:10, Serial0/0
Below is the config for all four routers for your further reference. Drop me an email to me at deepakarora.1984@gmail.com incase you face any issue or have some doubt or suggestions on this :-)
-------------------------------------------------------------------------------------------
R1#sh run
Building configuration...
Current configuration : 804 bytes
!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname R1
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
!
resource policy
!
memory-size iomem 5
ip cef
!
!
!
!
!
!
!
!
!
!
!
interface FastEthernet0/0
ip address 10.0.0.1 255.0.0.0
duplex auto
speed auto
!
interface Serial0/0
ip address 1.1.1.1 255.255.255.252
clock rate 2000000
!
interface FastEthernet0/1
no ip address
shutdown
duplex auto
speed auto
!
interface Serial0/1
no ip address
shutdown
clock rate 2000000
!
router ospf 1
router-id 25.25.25.25
log-adjacency-changes
network 1.1.1.1 0.0.0.0 area 0
network 10.0.0.1 0.0.0.0 area 0
!
!
ip http server
no ip http secure-server
!
!
control-plane
!
!
line con 0
line aux 0
line vty 0 4
!
!
end
--------------------------------------------------------------------------------------------
R2#sh run
Building configuration...
Current configuration : 1054 bytes
!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname R2
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
!
resource policy
!
memory-size iomem 5
ip cef
!
!
!
!
!
!
!
!
!
!
!
interface FastEthernet0/0
ip address 20.0.0.1 255.0.0.0
duplex auto
speed auto
!
interface Serial0/0
ip address 1.1.1.2 255.255.255.252
clock rate 2000000
!
interface FastEthernet0/1
no ip address
shutdown
duplex auto
speed auto
!
interface Serial0/1
ip address 2.2.2.1 255.255.255.252
clock rate 2000000
!
interface Serial0/2
no ip address
shutdown
clock rate 2000000
!
interface Serial0/3
no ip address
shutdown
clock rate 2000000
!
router ospf 1
router-id 50.50.50.50
log-adjacency-changes
area 1 range 192.168.8.0 255.255.252.0
area 1 virtual-link 75.75.75.75
network 1.1.1.2 0.0.0.0 area 0
network 2.2.2.1 0.0.0.0 area 1
network 20.0.0.1 0.0.0.0 area 1
!
!
ip http server
no ip http secure-server
!
!
control-plane
!
!
line con 0
line aux 0
line vty 0 4
!
!
end
------------------------------------------------------------------------------------------
R3#sh run
Building configuration...
Current configuration : 1572 bytes
!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname R3
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
!
resource policy
!
memory-size iomem 5
ip cef
!
!
!
!
!
!
!
!
!
!
!
interface Loopback0
ip address 192.168.8.1 255.255.255.0
ip ospf network point-to-point
ip ospf 1 area 1
!
interface Loopback1
ip address 192.168.9.1 255.255.255.0
ip ospf network point-to-point
ip ospf 1 area 1
!
interface Loopback2
ip address 192.168.10.1 255.255.255.0
ip ospf network point-to-point
ip ospf 1 area 1
!
interface Loopback3
ip address 192.168.11.1 255.255.255.0
ip ospf network point-to-point
ip ospf 1 area 1
!
interface Loopback4
no ip address
!
interface FastEthernet0/0
ip address 30.0.0.1 255.0.0.0
duplex auto
speed auto
!
interface Serial0/0
ip address 2.2.2.2 255.255.255.252
clock rate 2000000
!
interface FastEthernet0/1
no ip address
shutdown
duplex auto
speed auto
!
interface Serial0/1
ip address 3.3.3.1 255.255.255.252
clock rate 2000000
!
interface Serial0/2
no ip address
shutdown
clock rate 2000000
!
interface Serial0/3
no ip address
shutdown
clock rate 2000000
!
router ospf 1
router-id 75.75.75.75
log-adjacency-changes
area 1 range 192.168.8.0 255.255.252.0
area 1 virtual-link 50.50.50.50
area 2 range 172.16.8.0 255.255.252.0
network 2.2.2.2 0.0.0.0 area 1
network 3.3.3.1 0.0.0.0 area 2
network 30.0.0.1 0.0.0.0 area 2
!
!
ip http server
no ip http secure-server
!
!
control-plane
!
!
line con 0
line aux 0
line vty 0 4
!
!
end
------------------------------------------------------------------------------------------------
R4#sh run
Building configuration...
Current configuration : 1316 bytes
!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname R4
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
!
resource policy
!
memory-size iomem 5
ip cef
!
!
!
!
!
!
!
!
!
!
!
interface Loopback0
ip address 172.16.8.1 255.255.255.0
ip ospf network point-to-point
!
interface Loopback1
ip address 172.16.9.1 255.255.255.0
ip ospf network point-to-point
!
interface Loopback2
ip address 172.16.10.1 255.255.255.0
ip ospf network point-to-point
!
interface Loopback3
ip address 172.16.11.1 255.255.255.0
ip ospf network point-to-point
!
interface FastEthernet0/0
ip address 40.0.0.1 255.0.0.0
duplex auto
speed auto
!
interface Serial0/0
ip address 3.3.3.2 255.255.255.252
clock rate 2000000
!
interface FastEthernet0/1
no ip address
shutdown
duplex auto
speed auto
!
interface Serial0/1
no ip address
shutdown
clock rate 2000000
!
router ospf 1
router-id 100.100.100.100
log-adjacency-changes
network 3.3.3.2 0.0.0.0 area 2
network 40.0.0.1 0.0.0.0 area 2
network 172.16.8.1 0.0.0.0 area 2
network 172.16.9.1 0.0.0.0 area 2
network 172.16.10.1 0.0.0.0 area 2
network 172.16.11.1 0.0.0.0 area 2
!
!
ip http server
no ip http secure-server
!
!
control-plane
!
!
line con 0
line aux 0
line vty 0 4
!
!
end
Best Regards,
Deepak Arora
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