| 1: | Name one routing protocol that sends periodic updates. |
| A1: | RIPv1, RIPv2, and IGRP all send periodic updates. |
| 2: | What is an incremental update, and how often is it sent out? |
| A2: | An incremental update is an update that is sent out only when there is a change in the network. It contains only the information about the change. The change could be either the loss of a network or the addition of a network. EIGRP sends out incremental updates, as does OSPF, IS-IS, and BGP. |
| 3: | Distance vector routing protocols naturally summarize at which boundary? |
| A3: | Distance vector routing protocols naturally summarize at the IANA or major network boundary. They do this by following the first octet rule. |
| 4: | What is the algorithm used by distance vector protocols? |
| A4: | Distance vector routing protocols use the Bellman Ford algorithm. |
| 5: | Give three reasons why RIPv1 has problems working in a large network. |
| A5: | RIPv1 has problems working in a large network because of the following reasons: -
- It has a maximum hop count of 15. -
- It sends updates of its routing table out of every interface every 30 seconds, which increases the network overhead and leads to link congestion. -
- To avoid routing loops , it uses holddown and poison reverse, and thereby increases the time that it takes to propagate the changes in the network. |
| 6: | What is the destination address of the distance vector periodic update in RIPv1? |
| A6: | The destination address of the distance vector periodic update is 255.255.255.255 (the broadcast address). |
| 7: | State two ways that a route is selected as the preferred path . |
| A7: | A route is selected for the following reasons: -
- Because it is the only available path -
- Because the administrative distance is lower -
- Because the metric is lower |
| 8: | What is administrative distance? |
| A8: | Administrative distance is the mechanism used by the routing process to select a path offered by two different routing protocols. The administrative distance is a set of values, in which a value is given to each IP routing protocol. This allows a hierarchy to be established so that when multiple protocols offer a path to the same remote network, one path can be chosen. The path that is chosen will be the one offered by the routing protocol with the lowest administrative distance. The administrative distance can be manually configured. |
| 9: | If IGRP has three paths to a remote network in which each path has an equal metric, what will happen? |
| A9: | If IGRP sees equal-cost paths to a remote network, it will load balance between those paths by default. |
| 10: | A distance vector routing protocol uses the mechanism of poison reverse. What is poison reverse? |
| A10: | When the routing process suspects that a route in its routing table is no longer valid, it sets the metric so high for that route that it renders it unusable. This metric will be propagated in the routing updates to other routers. This mechanism is used in triggered updates. It is also used with split horizon. Instead of suppressing routes from being advertised out of the interface from which they were heard , it advertises the routes but sets the metric so high as to be rendered unusable. This is called split horizon with poison reverse. |
| 11: | Name two distance vector routing protocols. |
| A11: | Distance vector routing protocols include RIPv1, RIPv2, IGRP, and EIGRP (an advanced distance vector routing protocol). |
| 12: | Describe the mechanism of split horizon. |
| A12: | Split horizon is a routing technique in which information about routes is prevented from exiting the router interface through which that information was received. Split-horizon updates are useful in preventing routing loops. |
| 13: | What is meant by the phrase routing by rumor ? |
| A13: | Distance vector routing protocols are said to be "routing by rumor" because information is never sent or flooded to all routers but rather sent to neighbors who in turn forward their routing table. Distance vector protocols send periodic updates. These updates are sent to directly connected neighbors. The update is periodic because it waits for a timer to expire before it sends an update. After receiving a neighbor's routing table, the router updates its own table and sends the modified table in subsequent updates. |
| 14: | Why does the use of multicast addressing in RIPv2 overcome some of the limitations of RIPv1? |
| A14: | The use of the multicast addressing saves network resources because all the nodes in the network can discard the packet at either Layer 2 or Layer 3 instead of taking the packet all the way up to the transport layer, where the port number is rejected. Although this saves system resources, the same amount of bandwidth is consumed on each link that the multicast traverses. |
| 15: | Explain the use of holddown in distance vector routing protocols to create stability in the network. |
| A15: | The use of holddown is crucial to network stability. The term holddown refers to when and how the routing process decides that a route in the routing table is no longer valid. After deciding that a network in the routing table is no longer available, the routing process waits for three routing updates (by default) before it believes a routing update with a less-favorable metric. Again, this is to prevent routing loops from generating false information throughout the network. |
| 16: | What is the maximum hop count in RIPv1 and RIPv2? |
| A16: | The maximum hop count is 15 with infinity stated at 16. |
| 17: | Both EIGRP and IGRP use a composite metric. What are the main components of this metric? |
| A17: | Bandwidth, delay, reliability, and load are the interface values that are used for IGRP and EIGRP. |
| 18: | Explain briefly how RIPv2 differs from RIPv1. |
| A18: | RIPv2 differs from RIPv1 in the following ways: -
- The metric is a composite calculated from bandwidth, delay, loading, reliability, and MTU. In fact, although MTU was originally designed as part of the metric, it is tracked but not used in the calculation. It is possible to configure the use of all the calculated elements of the metric. If these are not configured, the system will use only bandwidth and delay by default. -
- The hop count is 100 and is configurable to 255 (although this is not used as a metric, but to age out datagrams). -
- The update timer is set by default to 90 seconds (three times that of RIPv1). -
- Unequal-cost load balancing occurs on multiple paths. -
- A more efficient packet structure is used. -
- Autonomous systems are used to allow multiple processes within a routing domain, which allows the network to scale. |
| 19: | What is meant by the term convergence ? |
| A19: | Convergence occurs when all the routers in the routing domain agree on the available routes. Convergence time is the time that it takes for every router's routing table to synchronize after there has been a change in the network topology. It is important to ensure that the time taken is as short as possible, because, while the routers disagree on the available networks, they cannot route data correctly or efficiently . |
| 20: | Give the configuration commands to turn on the process for RIPv2. |
| A20: | RouterA(config)# router rip RouterA(config-router)# version 2 |
