OSPF Lab (CCNA Lab 4)

General Description

It’s been a while since I did a full lab here, so it’s probably worth a quick few words. I’ve done two styles of lab exercises in this blog space. A “lab” typically has several parts, takes some time to work through all the config, and it takes me 4-5 posts to walk through the configs with you here in the blog. The other type, Config Virtual Museum (VM) labs, should only take you about 5 minutes to do the work; each VM piece is two posts only, with a problem statement and an answer.
Today’s post gives you the setup and tasks for an OSPF lab. For the setup, today’s post lists a figure of the lab topology, which has four routers. The lab also tells you the IP addresses and masks.
Other than the setup information, this post then lists requirements in four different parts. The parts just give me a way to break the lab up into manageable chunks for discussion in the blog; you can go ahead and work on all of it whenever you want. Just know that I won’t be talking about the answers to a particular part until the answers post appears for that part.
That’s the process. Figure 1 shows the important details of the setup information. You may also assume all the cables have been plugged in, and that the router interfaces work, and the routers can send frames over each interface.

Figure 1: Lab Topology and IP Addresses

Part 1: Configure IP Addresses and Enable OSPF

For completeness, configure the IP addresses and masks, as shown in the planning figure. Beyond that, enable OSPF on all interfaces shown in the figure as well. Put all interfaces in area 0.
When configuring OSPF, follow the additional requirements in Table 1. The requirements in Table 1 limit the number of options you have to configure each router. Why? OSPF allows so many variations in the configuration of the OSPF network command, these extra requirements help narrow down your options, so that when we discuss the answers, we do not have to go through twenty options for every single network command. Table 1 helps paint you into a corner regarding the OSPF network commands used on each router.

Table 1 – OSPF network Command Guidelines

Router	Instruction for Configuring network Commands
R1	Exactly match the IP address of each interface
R2	Exactly match all IP addresses in the subnet associated with an interface
R3	Match all interfaces in one network command
R4	Match all interfaces with one network command, but use a different wildcard mask than the one you used on R4

Part 2: Configure OSPF Authentication

The design gives us only three OSPF neighbor relationships. As usual, you have configuration options in this case, so to try and paint you into another corner, this part also gives you some requirements that may not be useful for real life, but will hopefully give us all a common couple of answers when done.
Follow these requirements, with the details in Table 2.

• Use the area OSPF subcommand as much as possible, to reduce the number of interface subcommands used for OSPF authentication.

Table 2 – OSPF Authentication Guidelines

Neighbor Relationship	Requirement
R1-R2	Type 0 Authentication
R1-R3	Type 1 Authentication
R1-R4	Type 2 Authentication

Part 3: Metric Tuning

For this next task, tune the configuration on the various routers to create different OSPF costs for some of the OSPF routes as listed here. As usual, the requirements listed here attempt to drive us towards a single answer, rather than make complete sense for real life, but it does give you a chance to think about tuning metrics.
For Table 3, configure the routers to cause the new metrics, with additional requirements listed before the table:

• Do not change the OSPF reference-bandwidth.
• For an added challenge, limit your new configuration to no more than one ip ospf cost interface subcommand among all the routers.

Table 3 – New Cost Requirements for Various Routes

For the Route on this Router…	For this Subnet…	… Make it Have this Cost
R2	R3’s LAN Subnet	133
R3	R2’s LAN Subnet	131
R2	R4’s LAN Subnet	166

To do this lab exercise, if you don’t have a place to play, it helps to know the OSPF costs for the original routes before changing any of the configurations. In this lab, if you have taken all defaults so far – in other words, you only configured what you were asked to configure – the costs can be predicted. The routers’ F0/0 interfaces will all have cost 1, and the routers’ serial interfaces will have cost 64. The math is based on the default reference bandwidth of 10^8 bits/second, versus the interface default bandwidth settings: 100 Mbps on FastEthernet, and 1.544 Mbps on the serial interfaces. For instance, R1’s routes to the other three routers’ LAN subnets will be 65: Cost 64 from one serial interface, plus cost 1 from one LAN interface.

Part 4: OSPF Router ID

In this case, configure the routers so that they use the OSPF router ID listed in table 4. Also follow the restrictions in table 4 as well, for the usual reasons.
Note: On a real router, the OSPF process sets the router ID (RID) when the process starts. In this case, just supply the configuration so that on the next reload, the routers will have the correct RID.

Table 4 – OSPF Router ID Configuration Requirements

Router	Desired Router ID	Restrictions
R1	1.0.0.9	None
R2	2.2.2.2	Do not use the router-id command
R3	1.3.3.3	Do not use the router-id command, and do not enable OSPF on the interface that has this IP address
R4	1.2.4.4	Do not use a loopback interface