Your are tasked with configuring the network shown in Figure 5-15 with OSPF such that:
- All interfaces on every router is added in OSPF.
- Router IDs for each router should be:
- RouterA – 220.127.116.11
- RouterB – 18.104.22.168
- RouterC – 22.214.171.124
- RouterD – 126.96.36.199
- RouterE – 188.8.131.52
- Any networks created for item 2 on this list should not be advertised in OSPF
- Router E never becomes the DR/BDR in the 184.108.40.206/29 network segment
- Router D is always the DR in in the 220.127.116.11/28 network segment
- RouterE should use RouterC to reach 18.104.22.168/16 network. The other path should be used for backup only.
- Remember that the DCE side of your DTE/DCE back to back cable should be connected to the interface configured with clock rate.
Figure 5-15 Network for Lab 5-3
The initial configuration of the routers is shown below:
Before configuring OSPF globally, configure RouterE with an OSPF priority of 0 and RouterD with a priority of 10 to complete item 4 and 5 in the list. Configuring these before adding networks in OSPF will ensure that DR/BDR is influence at the first go without having to restart OSPF process later.
Next, configure a loopback interface on each router to change the Router ID as given in item 1 in the list:
Next, configure OSPF on all routers as shown below. Remember not to use 0.0.0.0 255.255.255.255 to advertise networks since loopback interfaces should not be advertised as per item number 3 in the list.
Since RouterE has two equal cost paths to reach the 22.214.171.124/16 network, it will load balance across them. To disable load balancing, the cost needs to be changed as shown below:
To verify the solution, first take a look at the routing table of each router in the network:
In the above output notice the following:
1. All networks are seen across the internetwork
2. Loopback networks are not advertised across the network
3. RouterE has a route towards 126.96.36.199/16 network through 188.8.131.52 (RouterC)
Next, verify the DR/BDR election in the Ethernet segment by looking at the neighbor table on RouterE:
RouterE#sh ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
184.108.40.206 1 2WAY/DROTHER 00:00:39 220.127.116.11 FastEthernet0/0
18.104.22.168 1 FULL/BDR 00:00:31 22.214.171.124 FastEthernet0/0
126.96.36.199 10 FULL/DR 00:00:31 188.8.131.52 FastEthernet0/0
Notice that the RouterID of every router is as listed in item 2 of the list and that the RouterD is the DR.
Finally, ping the 184.108.40.206/16 network from RouterE to confirm that routing is working properly:
Phew! This was a big chapter and with a good reason too! As I mentioned earlier in the book, the CCNA certification is mostly about the network and the data-link layer. This chapter covered the most important aspect of the network layer – routing protocols. Here you got to know what binds a network together.
In this chapter you were introduced to all three routing protocol – RIP, EIGRP and OSPF. You learned the how each one operates and how to configure them. You also learned the difference between how each of these protocol works. I cannot stress enough the importance of this chapter. I strongly suggest re-reading the chapter and practicing configuring, verifying and troubleshooting them before moving to the next chapter because the next two chapters look at the data-link layer that is very different from the network layer.