Part 3 of this lab asks you to configure OSPF. For today’s post, I’ll focus on all the OSPF config requested in part 3 of this lab, except for the metric tuning, which I’ll defer for a final post for this lab. But there’s plenty to discuss today. The lab gives us the area design in a diagram; for the baseline config, the biggest challenges for this part are to remember the config commands, to translate between the figure and the area parameters on those commands, and how to use the wildcard mask parameter on the commands. Plus you have to set each router’s OSPF router ID on each router. Make sure and check out the original lab exercise to make sense of today’s post, which simply shows a solution to part of the lab.
To configure OSPF, you need to configure a number of OSPF network commands in OSPF configuration mode. The router ospf process-id global command moves you to OSPF configuration mode. Then you need to configure one or more network commands.
The network commands perform a couple of functions. First, they enable OSPF on one or more interfaces. How? They enable OSPF on interfaces whose interface IP addresses match the IP address/wildcard mask pair configured on the network command. Once you realize that comparison that is being made, you just need to have mastered ACL wildcard logic, because the wildcard mask on the OSPF network command uses that same logic.
Figure 3-5 shows the general idea of the logic, with one router that has three interfaces (IP addresses shown). The one generic network command in the figure shows that a comparison takes place between the network command’s IP address parameter. The wildcard mask gives you an opportunity to limit that comparison to a subset of the 32 bits of the address.
The network command also defines the area in which the matched interface(s) should be placed. For instance, you could configure a network command that matches multiple interfaces on a router; in that case, all the interfaces matched by that one network command would be placed into the area listed. If you want to put two different interfaces into two different areas, just make sure to use two network commands, and that the IP address/wildcard mask logic on each command matches only one of the interfaces.
Part 3 of the lab also tells you to assign OSPF router IDs of 1.1.1.1, 2.2.2.2, and so on. IOS pulls the OSPF router ID from one of three places, listed here in order of precedence:
To configure OSPF, you need to configure a number of OSPF network commands in OSPF configuration mode. The router ospf process-id global command moves you to OSPF configuration mode. Then you need to configure one or more network commands.
The network commands perform a couple of functions. First, they enable OSPF on one or more interfaces. How? They enable OSPF on interfaces whose interface IP addresses match the IP address/wildcard mask pair configured on the network command. Once you realize that comparison that is being made, you just need to have mastered ACL wildcard logic, because the wildcard mask on the OSPF network command uses that same logic.
Figure 3-5 shows the general idea of the logic, with one router that has three interfaces (IP addresses shown). The one generic network command in the figure shows that a comparison takes place between the network command’s IP address parameter. The wildcard mask gives you an opportunity to limit that comparison to a subset of the 32 bits of the address.
The network command also defines the area in which the matched interface(s) should be placed. For instance, you could configure a network command that matches multiple interfaces on a router; in that case, all the interfaces matched by that one network command would be placed into the area listed. If you want to put two different interfaces into two different areas, just make sure to use two network commands, and that the IP address/wildcard mask logic on each command matches only one of the interfaces.
Part 3 of the lab also tells you to assign OSPF router IDs of 1.1.1.1, 2.2.2.2, and so on. IOS pulls the OSPF router ID from one of three places, listed here in order of precedence:
- As configured on the router-id a.b.c.d OSPF subcommand
- It uses the numerically-highest IP address on any loopback interface which is also in an up/up state
- It uses the numerically-highest IP address on any non-loopback interface which is also in an up/up state
- Many different valid solutions exist that use a variety of wildcard masks. I just picked several for the sake of giving us more to discuss, should someone want to discuss them.
- For purposes of this lab, I’ll show routers R1 and R2 setting their OSPF RID using the first method in the earlier list, and routers R3 and R4 using the second.
- Figure 6 repeats the OSPF area design figure for convenience.
Example 9: OSPF Configuration Added, R1
router ospf 1 router-id 1.1.1.1 network 172.23.1.1 0.0.0.63 area 0 network 172.23.0.1 0.0.0.63 area 2 network 172.23.0.65 0.0.0.63 area 3 network 172.23.0.129 0.0.0.64 area 4 ! interface F0/0 ip address 172.23.1.1 255.255.255.192 ! interface serial 0/0/0 encapsulation frame-relay ! interface S0/0/0.1 point-to-point ip address 172.23.0.1 255.255.255.192 frame-relay interface-dlci 102 ! interface s0/0/0.2 point-to-point ip address 172.23.0.65 255.255.255.192 frame-relay interface-dlci 103 ! interface s0/0/0.3 point-to-point ip address 172.23.0.129 255.255.255.192 frame-relay interface-dlci 104
Example 10: OSPF Config Added, R2
router ospf 1 router-id 2.2.2.2 network 0.0.0.0 255.255.255.255 area 2 ! interface F0/0 ip address 172.23.2.1 255.255.255.192 ! interface serial 0/0/0 encapsulation frame-relay ! interface S0/0/0.1 point-to-point ip address 172.23.0.62 255.255.255.192 frame-relay interface-dlci 101
Example 11: FR Added to IP Configuration, R3
interface loopback 1 ip address 3.3.3.3 255.255.255.255 ! router ospf 1 network 172.23.3.1 0.0.0.63 area 3 network 172.23.0.126 0.0.0.63 area 3 ! interface F0/0 ip address 172.23.3.1 255.255.255.192 ! interface serial 0/0/0 encapsulation frame-relay ! interface S0/0/0.1 point-to-point ip address 172.23.0.126 255.255.255.192 frame-relay interface-dlci 101
Example 12: OSPF Config Added, R4
interface loopback 1 ip address 4.4.4.4 255.255.255.255 ! router ospf 4 network 172.23.4.1 0.0.0.0 area 4 network 172.23.0.190 0.0.0.1 area 4 ! interface F0/0 ip address 172.23.4.1 255.255.255.192 ! interface serial 0/0/0 encapsulation frame-relay ! interface S0/0/0.1 point-to-point ip address 172.23.0.190 255.255.255.192 frame-relay interface-dlci 101
