220.127.116.11 Do We Really Need a Map? (Instructor Version – Optional Lab)
Instructor Note: Red font color or gray highlights indicate text that appears in the instructor copy only. Optional activities are designed to enhance understanding and/or to provide additional practice.
Describe the primary functions and features of a router.
Routers send and receive information from networks they recognize. The routing table is a very important tool to supply the network administrator with information about how a network delivers data from source to destination between networks. This modeling activity focuses students’ thoughts on how routing is mapped and documented.
Using the Internet and Google Maps, located at http://maps.google.com, find a route between the capital city of your country and some other distant town, or between two places within your own city. Pay close attention to the driving or walking directions Google Maps suggests.
Notice that in many cases, Google Maps suggests more than one route between the two locations you chose. It also allows you to put additional constraints on the route, such as avoiding highways or tolls.
- Copy at least two route instructions supplied by Google Maps for this activity. Place your copies into a word processing document and save it for to use with the next step.
- Open the .pdf accompanying this modeling activity and complete it with a fellow student. Discuss the reflection questions listed on the .pdf and record your answers.
Be prepared to present your answers to the class.
- Internet connection
- Web browser
- Google Maps, http://maps.google.com/
1. What do the individual driving, or walking based on your criteria you input, and non-highway directions look like? What exact information do they contain? How do they relate to IP routing?
Each suggested route has its overall length and duration indicated. The two sets of directions consist of detailed step-by-step instructions to reach the other destination. At each significant crossing, you are advised of the very next direction to take and of the distance to the next crossroad.
These instructions closely resemble information in routing tables of IP-based routers. Each crossing can be likened to a router on which the next path selection takes place. The overall length and duration of the route correspond to the route metric, or a measure of its usefulness, from the source to the destination. The advice on which next direction to take from a particular crossing resembles an entry in the particular router’s routing table that contains information about the nearest next hop router on the path towards the destination. The distance to the next crossroad is similar to the so-called cost of an interface that is used by routing protocols to compute the resulting metric of a route.
2. If Google Maps offered a set of different routes, what makes this route different from the first? Why would you choose one route over another?
Multiple routes traverse different paths to them same destination. These paths may differ in various characteristics, as some take longer to complete from source to destination and others are physically longer due to distance; therefore, when comparing this activity to network travel, distance and time can make a difference to the routes displayed.
3. What criteria can be used to evaluate the usefulness of a route?
Criteria could include:
- the number of different paths are available from source to destination, such as direct connections, through other routers;
- the time it takes to send data from source to destination, which can be based on bandwidth and delay;
- the reliability of the route from source to destination, such as static vs. dynamic routes;
- whether the route is the preferred route or a secondary route, such as static routes, default routes and other reported routes;
- which speeds can be used to move packets from source to destination, such as the type of media/medium used to connect networks.
4. Is it sensible to expect that a single route can be “the best one”, i.e. meeting all various requirements? Justify your answer.
If the route given meets all the criteria requested, the single route can be the best route. Compare this to a default route or the only route available from source to destination.
5. As a network administrator or developer, how could you use a network map, or routing table, in your daily network activities?
Network maps or routing tables can be used to envision and document the best paths for data delivery on networks. They can also be used to structure a direct path, or direct paths, from one network to another.
Modeling Activity Graphic Representation (designs will vary)
Instructor Note: Listed below is representative output from the Google Maps site for Instructor use only.
Identify elements of the model that map to IT-related content:
- Routing Table
- Administrative Distance
- Default Route
- Static Route