ECE 4110 Internetwork Programming
Lab 8: OSPF and Fixing Broken Networks
Group Number: ______
Member Names: ______
Date Issued: October 29, 2008
Turn-in Due: November 5, 2008
This lab requires that you use one of three setups. If a signup sheet has been posted, you must sign up in advance on the lab door. You mayreserve each setup for no more than 2 hours at a time. You must use the same setup each time you work on this lab. A TA must be present for two checkoffs of this lab. Also, it would be useful to bring your ECE4110 Lab 5 documentation to help you in troubleshooting the network.
Goal
When you begin this lab, there will be several problems in the OSPF network. Your job will be to find and repair the problems. Once you believe you have correctly repaired the network, a TA will check you off after you reach the designated check-off point (there are two check-off points in this lab).
Prelab Questions
Answer the following questions on a separate sheet of paper, and include your answers with your lab report.
1) What are the differences between a distance vector and a link-state routing protocol? What kind of routing protocol is OSPF?
2) What IP protocol number does OSPF use?
3) What are the mechanisms used by OSPF routers to exchange routing information? Describe them.
4) What is VLSM? Does OSPF support it? Justify your answer.
5) How does OSPF determine the metric/cost for a route?
6) Why does not OSPF need any mechanism (e.g., split horizon for RIP) to prevent the occurence of rouitng loops?
7) Compared to OSPF, what is the limitation of RIP in terms of the size of networks?
8) How does OSPF achieve routing scalability to reduce LSAs traffic in a large network?
Lab Scenario
At the end of this lab, your network should look like the one pictured below:
:
Section 1: Troubleshooting a Network
For this lab we have three hardware setups. When you signed up for time in the lab you should have signed up for a particular playstation: 1, 2, or 3. For the entirety of this lab, c denotes your playstation number. As with the previous lab, make certain that no one else is using your setup before beginning work on the lab.
In a network, there are often several points of possible failures. Three of the most common reasons why a network is not working properly are:
The physical connection between two nodes in the network has been compromised, such as the cable being damaged or one of the nodes being unplugged. You will not encounter this problem in this lab.
The routing table in one or more of the computers or routers is misconfigured.
One or more of the interfaces on one or more computers or routers has been misconfigured or is down due to any reason.
Unlike the last lab, we are now using OSPF to route our packets. In OSPF we do not need to explicitly define our neighbors in order to route; the hello protocol will perform automatic discovery.
Use the following table to identify your routers and switch.
Playstation 1 / Playstation 2 / Playstation 3Switch / 5 / 14 / 23
OSPF 1 Router / 7 / 16 / 25
OSPF 2 Router / 8 / 17 / 26
OSPF 3 Router / 9 / 18 / 27
OSPF 4 Router / 10 / 19 / 28
OSPF 5 Router / 11 / 20 / 29
To begin the lab, you need to get a TA to upload the broken network to your playstation. They will sign off that it is indeed broken.
1st TA Signoff – Broken Network: TA has to make sure that routers are loaded properly broken.
Log into the computer marked ECE 4110 Labs 6,7 Setup c. This is the machine marked Linux Computer 1 in our network diagram on page 2. The username is root and the password is password
Telnet into OSPF1 by typing:
telnet 10.c.1.1
The telnet password is owen. Enable, then type show ip route. Notice that not all of the subnets on our diagram are present in the output. This indicates that there is something wrong with the network. Save your output from the show ip route command and include it in your lab report.
Log into ECE 4110 Lab 8 Setup c Computer 2. This is the machine marked Linux Computer 2 on our network diagram on page 2. Your username and password are again root and password. Try to ping Linux Computer 1 from Linux Computer 2. This ping should fail.
There are several problems in the network, although none of them involve physical connection issues. Your job is to use the commands you have learned in previous labs to fix the network so that it functions like the network diagramed on page 2. Once you are done fixing the errors, you should be able to ping Linux Computer 1 from Linux Computer 2 and vice versa.
In addition to being able to ping the opposite station, you must make sure that all links in the given network diagram are active. You will not get full credit on the lab report if the network does not entirely match the diagram, even if you receive a check off.
Hints:
From each of the Linux machines try pinging every router. Once you have noted which routers cannot be pinged, you should have a better idea of which links may be down.
Remember, there are several possible sources of failures as mentioned above. Log onto each of the routers and verify that the routing tables are correct. Run show ip route and show running-config on each of the routers and compare the shown routing tables with what should be expected based on the network diagram.
You may ask TAs about the function of specific router configuration commands. You may not ask TAs how to solve specific routing problems.
There may also be problems with the way the switch is configured. Nothing is guaranteed to work correctly.
Once you have fixed the network, screenshot the routing table on OSPF1 again and include it in your lab report.
Section 2: Observing OSPF
Now that we have fixed our network, we will look specifically at how OSPF responds to changes in the network. Connect to OSPF1 and observe the output to the following command
1.show ip route
a) Are all the networks indicated in the diagram in the routing table?
b) How many routes are there for the network 10.c.8.0/24? Why?
c) Comment on one difference between where packets are routed in this table and where they would be routed if you were running RIP.
Telnet to 10.c.3.2 (OSPF3), then shutdown the interface FastEthernet0/0. Keep track of when you typed shutdown (start a stopwatch if you have one). Note that you have simulated a network failure: interface 10.c.7.2 on OSPF3 no longer works.
Return to OSPF1, and look at the routing table by typing show ip route.If your routing table is unchanged, keep trying until it does change.
2.a)What routes do you see? b) Is the routing table different from before? If so, how? c) How long did it take your routing table to change? d) Why? How does this compare to RIP?
Telnet back into OSPF3 and Re-enable FastEthernet0/0 with the no shutdown command.
Ping Linux Computer 1 from Linux Computer 2 and simultaneously ping Linux Computer 2 from Linux Computer 1. Show this ping to the TA.
2nd TA Signoff – Fixed Network: TA has to make sure that ping works properly.
Answer the following questions:
3.a) What was wrong with the network? Include the network drawing on page 3 with X’s over the links/interfaces that were broken.
3.b) How did you go about fixing the problem?
4. a)What are the differences in the routing table for OSPF1 as compared to when the network was broken? b) How did OSPF1 learn about the other subnets?
c) How are packets routed from Linux Computer 2 to 10.c.3.2? Why?
d) Do you prefer OSPF or RIP? Why?
e) Observe your routing table for OSPF1. Write the path taken to each of the eight networks, and state why each cost is its current value.
(Ex. To go to 10.1.10.0/24, the path is 10.1.11.2 (cost 3) to 10.1.23.2 (cost 13) to 10.1.10.0 (cost 2) for a total cost of 18.)
Turn-In Checklist
Write a report that includes answers to all the bold questions in this lab. Explain in detail exactly what was wrong with the network and how you discovered and fixed the problems. Include your answers to the pre-lab questions with this report. Include the routing tables from OSPF1, the router configurations from all four routers, and any other data that you captured.
□Prelab questions and answers.
□All lab questions and answers. Include any requested screenshots.
□Router Configuration Files (You get these by running the download script. Just print out the switch and 5 routers ones and turn them in.)
□Group number on first page