Lesson 42 - OSPF Fundamentals Part 5 - The Lab

I try to keep these posts as short and informative as possible. Since it takes a moment to do this lab and analyze the results, the troubleshooting section is going to be included in the form of a video presentation at the end of this post (available soon).

Here is our topology. I have removed Frame-Relay links as it goes beyond the scope of this tutorial (some really crazy workbook/journal I started a few days ago might give you an idea about this complexity.

But let's get back to business!

Pic. 1 - OSPF Topology Diagram.

Icons designed by: Andrzej Szoblik - http://www.newo.pl

Since there are five different routers and three types of networks (broadcast, point-to-point and loopback) I will create an action plan and implement it step by step. I'll include some stipulations in order to show you a few things which I might have not talked about yet.

Task List

General Requirements:

• ALL interfaces should be enabled in area 0. 
• ALL loopback addresses must be advertises with their configured network mask length (/24) or (/28). 

1. Enable OSPF in the broadcast network connecting R1, R2 and R3. Make sure that R1 is elected the DR and R2 is elected the BDR in the broadcast segment (172.31.123.0/24).
2. Advertise the loopback subnets on R1, R2 and R3. On R3 do NOT use the network statement to advertise the subnet of Loopback1. On R3, while enabling OSPF on Loopback2 using the 'network' statement, use the wildcard bits corresponding to the network mask configured (/28).
3. Enable OSPF between R1 and R4. Advertise the subnet found on R4's loopback0.
4. Enable OSPF between R2 and R5. On R5 use only one network statement to enable OSPF on ALL interfaces (also the ones created in the future).
5. Enable the Simple Password authentication in area 0. Use the password 'cisco'.

Lab Solution

Step 1
Enable OSPF in the broadcast network connecting R1, R2 and R3.

Note!
Configuration must be done in this order to ensure R1 is elected the DR, R2 is elected the BDR.

R1 Configuration:

!

R1#conf t

R1(config)#interface f1/0

R1(config)#ip ospf priority 20

R1(config-if)#router ospf 1
R1(config-router)#router-id 1.1.1.1
R1(config-router)#network 172.31.123.1 0.0.0.0 area 0
R1(config-router)#exit  

R2 Configuration:

!

R2#conf t

R2(config)#interface f1/0

R2(config-if)#ip ospf priority 10

R2(config-if)#router ospf 1
R2(config-router)#router-id 2.2.2.2
R2(config-router)#network 172.31.123.2 0.0.0.0 area 0

R2(config-router)#exit

R3 Configuration:

!

R3#conf t

R3(config)#router ospf 1
R3(config-router)#router-id 3.3.3.3
R3(config-router)#network 172.31.123.3 0.0.0.0 area 0

R3(config-router)#exit

Now, let's give the routers a few seconds to go through the finding neighbors, creating adjacencies. Then a quick verification step shows the following:

Pic. 2 - OSPF Adjacencies.

R3 is adjacent with R1 (DR) and R2 (BDR).

Step 2
Advertise the loopback subnets on R1, R2 and R3. On R3 do NOT use the network statement to advertise the subnet of Loopback1. 

Note!
Loopback interfaces are considered the 'stub' networks by OSPF process and advertised with /32 network mask by default. In order to change it, the 'ip ospf network point-to-point' should be used on loopback interfaces.

Note!
After you have enabled OSPF on the loopbacks, you should check before proceeding to the next router's configuration. Use the following command:
Router#show ip ospf int brief 

R1 Configuration:

!

R1(config)#

R1(config)#interface loopback 1

R1(config-if)#ip ospf network point-to-point

R1(config-if)#router ospf 1

R1(config-router)#network 172.31.1.1 0.0.0.0 area 0

R1(config-router)#exit

R2 Configuration:

!

R2(config)#

R2(config)#interface loopback 1

R2(config-if)#ip ospf network point-to-point

R2(config-if)#router ospf 1

R2(config-router)#network 172.31.2.1 0.0.0.0 area 0

R2(config-router)#exit

Note!
The task stipulates that the subnet of Loopback1 must NOT be advertised like others (no network statement). Also, while enabling OSPF on the Loopback2 use the wildcard mask corresponding to the network mask configured there (/28).

R3 Configuration:

!

R3(config)#
R3(config)#interface loopback 2
R3(config-if)#ip ospf network point-to-point

R3(config-if)#interface loopback 1

R3(config-if)#ip ospf network point-to-point

R3(config-if)#ip ospf 1 area 0

R3(config-if)#router ospf 1

R3(config-router)#network 172.31.3.16 0.0.0.15 area 0

R3(config-router)#

Step 3
Enable OSPF between R1 and R4. Advertise the subnet found on R4's loopback1. 

R1 Configuration:

!

R1(config)#

R1(config)#router ospf 1

R1(config-router)#

R1(config-router)#network 172.31.14.1 0.0.0.0 area 0

R1(config-router)#exit

R4 Configuration:

!

R4(config)#interface loopback1

R4(config-if)#ip ospf network point-to-point

R4(config-if)#router ospf 1

R4(config-router)#router-id 4.4.4.4

R4(config-router)#network 172.31.14.4 0.0.0.0 area 0

R4(config-router)#network 192.168.4.1 0.0.0.0 area 0
R4(config-router)#exit

Step 4
Enable OSPF between R2 and R5. On R5 use only one network statement to enable OSPF on ALL interfaces (also the ones created in the future).

R2 Configuration:

!

R2(config)#

R2(config)#router ospf 1

R2(config-router)#network 172.31.25.2 0.0.0.0 area 0
R2(config-router)#exit

R5 Configuration:

!

R5(config)#interface loopback1

R5(config-if)#ip ospf network point-to-point

R5(config-if)#router ospf 1
R5(config-router)#router-id 5.5.5.5
R5(config-router)#network 0.0.0.0 255.255.255.255 area 0
R5(config-router)#exit

Note!
Of course, before you proceed to the the final step (OSPF authentication) you should check if all neighbors are adjacent and all routers can reach all the addresses in the network.

Step 5
Enable the Simple Password authentication in area 0. Use the password 'cisco'.

Note!
This configuration is going to break and re-establish OSPF adjacency.

R1 Configuration:

!

R1(config)#

R1(config)#router ospf 1

R1(config-router)#area 0 authentication

R1(config-router)#int f1/0

R1(config-if)#ip ospf authentication-key cisco

R1(config-if)#int s0/2

R1(config-if)#ip ospf authentication-key cisco

R2 Configuration:

R2(config)#

R2(config)#router ospf 1

R2(config-router)#area 0 authentication

R2(config-router)#int f1/0

R2(config-if)#ip ospf authentication-key cisco

R2(config-if)#int s0/2

R2(config-if)#ip ospf authentication-key cisco

R3 Configuration:

R3(config)#

R3(config)#router ospf 1

R3(config-router)#area 0 authentication

R3(config-router)#int f1/0

R3(config-if)#ip ospf authentication-key cisco

R4 Configuration:

R4(config)#

R4(config)#router ospf 1
R4(config-router)#area 0 authentication
R4(config-router)#int s0/2
R4(config-if)#ip ospf authentication-key cisco

R5 Configuration:

R5(config)#

R5(config)#router ospf 1
R5(config-router)#area 0 authentication
R5(config-router)#int s0/2
R5(config-if)#ip ospf authentication-key cisco

After OSPF authentication has been configured you should check if all the adjacencies have been formed and reachability is restored. If you have a problem with this lab in the troubleshooting sections you will find some tips helping you make this lab work.

Troubleshooting

Troubleshooting short videos available soon.

During the weekend your colleague, who's newly hired junior network administrator, was re-configuring your system. He has accidentally erased all backup configurations and also lost the track of all changes that he introduced. You have been called to help him restore the system.

Initial diagnostics the junior administrator has performed revealed the following problems:

Ticket 1
The subnets: 172.31.3.0/28 and 172.31.3.16/28 are no longer reachable from any other router but R3 (loopback1 and loopback2 on R3).

Video Presentation:
http://www.youtube.com/watch?v=vKZASyZbDmE

Ticket 2
R4 lost connectivity to all subnets in the network except for directly connected ones.

Video Presentation:
http://www.youtube.com/watch?v=HEOrvxKmQSU

Ticket 3
R5 lost connectivity to all subnets in the network except for directly connected ones.

Video Presentation:
http://www.youtube.com/watch?v=BlS3Z5kV_Rk

Final Verification
Ping using Tcl script - an elegant way of checking connectivity.

Video Presentation:
http://www.youtube.com/watch?v=VuubpKq0rxg

The next post is going to be an introduction to EIGRP routing protocol.