OSPf area routing Experiment (original)

I saw the following topic and asked which route was chosen when R4 arrived at R2. At that time, I was not sure. So I designed this topology to prove it and finally proved my conclusion. If the COST of R2.

In this topology, there is no difference between O routes and OIA routes at all, because OSPF is a link-State routing protocol, and R4 routes from two different links to R2 are OIA routes.

 

The topology is as follows:

 

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The configuration is as follows:

R1 Configuration

Interface Loopback0
Ip address 1.1.1.1 255.255.255.255

Interface Serial1/1
Ip address 10.10.12.1 255.255.255.252
Serial restart-delay 0
!
Interface Serial1/2
Ip address 10.10.14.1 255.255.255.252
Encapsulation frame-relay
Serial restart-delay 0
Frame-relay map ip 10.10.14.2 104 broadcast // The broadcast parameter here does not mean that OSPF can be broadcast in the HELLO packet.
No frame-relay inverse-arp
!

Router ospf 100
Router-id 1.1.1.1
Log-adjacency-changes
Network 1.1.1.1 0.0.0.0 area 1
Network 10.10.12.0 0.0.0.3 area 1
Network 10.10.14.0 0.0.3 area 1
Neighbor 10.10.14.2 // you must specify a neighbor here and use unicast to create a neighbor. Because the OSPF network type in the frame relay network is non-broadcast multi-channel access, you must specify a neighbor.

// Specify the neighbor. You must use the direct connection interface.

R2 Configuration

Interface Loopback0
Ip address 2.2.2.2 255.255.255.255

Interface Serial1/0
Ip address 10.10.12.2 255.255.255.252
Serial restart-delay 0
Clock rate 64000
!
Interface Serial1/1
Ip address 10.10.23.1 255.255.255.252
Serial restart-delay 0
Clock rate 64000

Router ospf 100
Router-id 2.2.2.2
Log-adjacency-changes
Network 2.2.2.2 0.0.0.0 area 0
Network 10.10.12.0 0.0.0.3 area 1
Network 10.10.23.0 0.0.0.3 area 0
!

R3 Configuration

Interface Loopback0
Ip address 3.3.3.3 255.255.255.255

Interface Serial1/0
Ip address 10.10.23.2 255.255.255.252
Serial restart-delay 0
!
Interface Serial1/1
Ip address 10.10.34.1 255.255.255.252
Serial restart-delay 0
Clock rate 64000

Router ospf 100
Router-id 3.3.3.3
Log-adjacency-changes
Network 3.3.3.3 0.0.0.0 area 0
Network 10.10.23.0 0.0.0.3 area 0
Network 10.10.34.0 0.0.0.3 area 1

R4 Configuration

Interface Loopback0
Ip address 4.4.4.4 255.255.255.255

Interface Serial1/0
Ip address 10.10.34.2 255.255.255.252
Serial restart-delay 0

 

Interface Serial1/2
Ip address 10.10.14.2 255.255.255.252
Encapsulation frame-relay
Ip ospf priority 100
Serial restart-delay 0
Frame-relay map ip 10.10.14.1 401 broadcast
No frame-relay inverse-arp

Router ospf 100
Router-id 4.4.4
Log-adjacency-changes
Network 4.4.4.4 0.0.0.0 area 1
Network 10.10.14.0 0.0.3 area 1
Network 10.10.34.0 0.0.0.3 area 1
Neighbor 10.10.14.1 // specify the neighbor. You must use the direct connection interface.

R1 route table:

R1 (config) # do sh 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, 1 subnets
C 1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O ia 2.2.2.2 [110/65] via 10.10.12.2, 01:57:18, Serial1/1
3.0.0.0/32 is subnetted, 1 subnets
O ia 3.3.3.3 [110/129] via 10.10.14.2, 01:57:18, Serial1/2
[110/129] via 10.10.12.2, 01:57:18, Serial1/1
4.0.0.0/32 is subnetted, 1 subnets
O 4.4.4.4 [110/65] via 10.10.14.2, 01:57:18, Serial1/2
10.0.0.0/30 is subnetted, 4 subnets
C 10.10.12.0 is directly connected, Serial1/1
C 10.10.14.0 is directly connected, Serial1/2
O ia 10.10.23.0 [110/128] via 10.10.12.2, 01:57:18, Serial1/1
O 10.10.34.0 [110/128] via 10.10.14.2, 01:57:29, Serial1/2

R1 # traceroute 3.3.3.3

Type escape sequence to abort.
Tracing the route to 3.3.3.3

1 10.10.14.2 40 msec
10.10.12.2 8 msec
10.10.14.2 24 msec
2 10.10.23.2 80 msec
10.10.34.1 76 msec *

We can see that there are two links between R1 and R3, and COST is equal, load is performed.

 

R4 # sh 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, 1 subnets
O 1.1.1.1 [110/65] via 10.10.14.1, 02:03:32, Serial1/2
2.0.0.0/32 is subnetted, 1 subnets
O ia 2.2.2.2 [110/129] via 10.10.34.1, 02:03:32, Serial1/0
[110/129] via 10.10.14.1, 02:03:32, Serial1/2
3.0.0.0/32 is subnetted, 1 subnets
O ia 3.3.3.3 [110/65] via 10.10.34.1, 02:03:32, Serial1/0
4.0.0.0/32 is subnetted, 1 subnets
C 4.4.4.4 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 4 subnets
O 10.10.12.0 [110/128] via 10.10.14.1, 02:03:32, Serial1/2
C 10.10.14.0 is directly connected, Serial1/2
O ia 10.10.23.0 [110/128] via 10.10.34.1, 02:03:32, Serial1/0
C 10.10.34.0 is directly connected, Serial1/0
R4 #
R4 # tr
R4 # traceroute 2.2.2.2

Type escape sequence to abort.
Tracing the route to 2.2.2.2

1 10.10.34.1 68 msec
10.10.14.1 4 msec
10.10.34.1 16 msec
2 10.10.12.2 52 msec
10.10.23.1 28 msec *
R4 #

The same is true for R4, where load occurs.

 

This article from "another pair of eyes BLOG", please be sure to keep this source http://xingno.blog.51cto.com/454158/385301