SEMESTER 2 Chapter 4 Distance Vector Routing Protocols V 4.0 RIP, IGRP, EIGRP

Transcription

1 SEMESTER 2 Chapter 4 Distance Vector Routing Protocols V What are the three distance vector routing protocols? What are the key characteristics of RIP? What are the key characteristics of IGRP? What are the key characteristics of EIGRP? How are distance vector routes advertised? Does a router in a distance vector network have knowledge of the entire path to a destination network? What are the 2 things a distance vector router knows? What are the two reasons sending an entire routing table in an update inefficient? What is the periodic update time for RIP? What is the periodic update time for IGRP? What is the address for broadcast updates? RIP, IGRP, EIGRP Hop count is used as the metric for path selection. If the hop count for a network is greater than 15, RIP cannot supply a route to that network. Routing updates are broadcast or multicast every 30 seconds, by default. Bandwidth, delay, load and reliability are used to create a composite metric. Routing updates are broadcast every 90 seconds, by default. IGRP is the predecessor of EIGRP and is now obsolete. It can perform unequal cost load balancing. It uses Diffusing Update Algorithm (DUAL) to calculate the shortest path. There are no periodic updates as with RIP and IGRP. Routing updates are sent only when there is a change in the topology. As vectors of distance and direction No The direction or interface in which packets should be forwarded and The distance or how far it is to the destination network consume bandwidth but also consume router CPU resources to process the updates 30 Sec 90 Sec What is the algorithm used for? to calculate the best paths and then send that information to the neighbors What processes does the routing protocol define? Mechanism for sending and receiving routing information. Mechanism for calculating the best paths and installing routes in the routing table. Mechanism for detecting and reacting to topology changes.

2 4.1.4 Define Time to Convergence. Time to convergence defines how quickly the routers in the network topology share routing information and reach a state of consistent knowledge. The faster the convergence, the more preferable the protocol. Routing loops can occur when inconsistent routing tables are not updated due to slow convergence in a changing network. Define Scalability. Scalability defines how large a network can become based on the routing protocol that is deployed. The larger the network is, the more scalable the routing Define Classless (Use of VLSM) or Classful. Define Resource Usage. Define Implementation and Maintenance List the advantages for distance vector protocols. List the disadvantages for distance vector protocols Definitely practice the exercise at the right. It will help you remember each protocol What are the routes that router will initially discover after booting? After completing the initial discovery what does the router start to do? What does the initial exchange of routing information contain? What does the router do with the information that is not contained in its routing table? After the first exchange of routing updates what has been protocol needs to be. Classless routing protocols include the subnet mask in the updates. This feature supports the use of Variable Length Subnet Masking (VLSM) and better route summarization. Classful routing protocols do not include the subnet mask and cannot support VLSM. Resource usage includes the requirements of a routing protocol such as memory space, CPU utilization, and link bandwidth utilization. Higher resource requirements necessitate more powerful hardware to support the routing protocol operation in addition to the packet forwarding processes. Implementation and maintenance describes the level of knowledge that is required for a network administrator to implement and maintain the network based on the routing protocol deployed. Simple implementation and maintenance Low resource requirements Slow convergence Limited scalability Routing loops The directly connected networks Exchange information Information about their directly connected networks It is added to the routing table Neighbors directly connected routes added to each routing table? What is convergence? When all routers have consistent knowledge of the network

3 What is slit horizon? Prevents information from being sent out the interface that it was received The amount of time it takes for the size of that network a network to converge is directly proportional to The speed of achieving convergence consists of what two things? How quickly the routers propagate a change in the topology in a routing update to its neighbors. The speed of calculating best path routes using the What are the two reasons routers exchange routing updates? What is the period update time for RIP? What are the four reasons listed for topology changes? What are the three additional timers? If an update has not been received to refresh an existing route after 180 seconds, what happens to that route in the routing table? What happens to the route after 240 seconds have elapsed? What does a holddown timer do? new routing information collected. To exchange routing information with their neighbors and to maintain up-to-date routing information in the routing table 30 seconds Failure of a link Introduction of a new link Failure of a router Change of link parameters Invalid Flush Holddown It is marked invalid It is removed from the routing table. Flushed Keeps a route in the routing table, marked as unreachable, for at least 180 seconds so all other routers receive that information Show ip route Show ip protocols What are the two commands that will show the timers? Define bounded update. Updates that are sent only to the routers that need the information instead of sending information to all routers What are characteristic of EIGRP updates? Non-periodic because they are not sent out on a regular basis. Partial updates sent only when there is a change in topology that influences routing information. Bounded, meaning the propagation of partial updates are automatically bounded so that only those routers that need the information are updated What is a triggered update? a routing table update that is sent immediately in response to a routing change What are the three reasons to An interface changes state (up or down) send a triggered update? A route has entered (or exited) the "unreachable" state A route is installed in the routing table What are the two problems with Packets containing the update message can be

4 triggered updates? What is it called when all the routers send updates at the same time on a network with a hub at the center? It this a problem on a switched dropped or corrupted by some link in the network. The triggered updates do not happen instantaneously. It is possible that a router that has not yet received the triggered update will issue a regular update at just the wrong time, causing the bad route to be reinserted in a neighbor that had already received the triggered update. Synchronized updates No network? What is a routing loop? a packet is continuously transmitted within a series of routers without ever reaching its intended destination network What are some reasons for routing loops? What mechanism is built into IP to overcome routing loops? What conditions can be created because of routing loops? What are some of the mechanisms used to avoid routing loops? Incorrectly configured static routes Incorrectly configured route redistribution (redistribution is a process of handing the routing information from one routing protocol to another routing protocol and is discussed in CCNP-level courses) Inconsistent routing tables not being updated due to slow convergence in a changing network Incorrectly configured or installed discard routes TTL time-to-live Link bandwidth will be used for traffic looping back and forth between the routers in a loop. A router's CPU will be strained due to looping packets. A router's CPU will be burdened with useless packet forwarding that will negatively impact the convergence of the network. Routing updates may get lost or not be processed in a timely manner. These conditions would introduce additional routing loops, making the situation even worse. Packets may get lost in "black holes." Defining a maximum metric to prevent count to infinity Holddown timers Split horizon Route poisoning or poison reverse Triggered updates What is count to infinity? a condition that exists when inaccurate routing updates increase the metric value to "infinity" for a network that is no longer reachable What is infinity defined by? Maximum metric value What is infinity for RIP? What is it called when a route goes up, then down, then up flapping

5 etc.? What are holddown timers used for? Describe the process of how a holddown timer works. to prevent regular update messages from inappropriately reinstating a route that may have gone bad. 1. A router receives an update from a neighbor indicating that a network that previously was accessible is now no longer accessible. 2. The router marks the network as possibly down and starts the holddown timer. 3. If an update with a better metric for that network is received from any neighboring router during the holddown period, the network is reinstated and the holddown timer is removed. 4. If an update from any other neighbor is received during the holddown period with the same or worse metric for that network, that update is ignored. Thus, more time is allowed for the information about the change to be propagated. 5. Routers still forward packets to destination networks that are marked as possibly down. This allows the router to overcome any issues associated with intermittent connectivity. If the destination network truly is unavailable and the packets are forwarded, black hole routing is created and lasts until the holddown timer expires What is the split horizon rule? a router should not advertise a network through the interface from which the update came What is route poisoning? to mark the route as unreachable in a routing update that is sent to other routers What is split horizon with poison reverse? when sending updates out a specific interface, designate any networks that were learned on that interface as unreachable What is time-to-live (TTL)? an 8-bit field in the IP header that limits the number of hops a packet can traverse through the network before it is discarded What happens when a packet s TTL reaches 0? What are the factors that affect the distance vector protocol you choose? What are the features of RIP? What features were introduced with RIPv2? The packet is discarded Size of the network Compatibility between models of routers Administrative knowledge required Supports split horizon and split horizon with poison reverse to prevents loops. Is capable of load balancing up to six equal cost paths. The default is four equal cost paths. Includes the subnet mask in the routing updates, making it a classless routing protocol. Has authentication mechanism to secure routing table updates. Supports variable length subnet mask (VLSM). Uses multicast addresses instead of broadcast.

6 What are the features of EIGRP? What are the advantages of EIGRP? Supports manual route summarization. Triggered updates (EIGRP has no periodic updates). Use of a topology table to maintain all the routes received from neighbors (not only the best paths). Establishment of adjacencies with neighboring routers using the EIGRP hello protocol. Support for VLSM and manual route summarization. These allow EIGRP to create hierarchically structured large networks. Although routes are propagated in a distance vector manner, the metric is based on minimum bandwidth and cumulative delay of the path rather than hop count. Fast convergence due to Diffusing Update Algorithm (DUAL) route calculation. DUAL allows the insertion of backup routes into the EIGRP topology table, which are used in case the primary route fails. Because it is a local procedure, the switchover to the backup route is immediate and does not involve the action in any other routers. Bounded updates mean that EIGRP uses less bandwidth, especially in large networks with many routes. EIGRP supports multiple network layer protocols through Protocol Dependent Modules, which include support for IP, IPX, and AppleTalk. * What are the examples of distance routing protocol? * What are the characteristics of EIGRP? * What are the characteristics of RIP? * What are the advantages of EIGRP over RIP?

7 * What is the routing loop? * What could cause the routing loop? * How does RIP v1 send its routing table update? How does RIP v2 send its routing table update? How often does it send the update? What is included in the update?

8 * RIP Triggered Updates Routing table update that is sent immediately to adjacent routers in response to a routing change The receiving routers, in turn, generate triggered updates that notify their neighbors of the change. * What 3 event will trigger the triggered update to take place in distance vector routing protocol? Interface changes state Route becomes unreachable Route is placed in routing table * What does the 1 st thing router do regarding to the network discovery after the boot-up (or the reload or the cold start)? [Hint: not the route exchange]

9 * What is Hold-down timer and what does it prevent from happing to the routing table? * What is the definition of infinity in RIP? * What is the definition of RIP_JITTER? * What is the definition of split horizon and how does it work?

10 * What is the definition of route poisoning and how does it work? * What is the purpose of TTL? How does it work to prevent loop on a network? Purpose of the TTL field The TTL field is found in an IP header and is used to prevent packets from endlessly traveling on a network How the TTL field works TTL field contains a numeric value. The numeric value is decreased by one by every router on the route to the destination. If numeric value reaches 0 then Packet is discarded. * What are the purposes of the following timers and how long is each timer? - Update timer? - Invalid timer? - Holddown timer? - Flush timer?

11 * What is the definition of networks are converged? What are the consequences if the distance vector networks cannot get converged? * Will the router forward any packet if the routing tables are not converged? * What are the consequences if the router forwards the packet when the networks are not converged? * What happen when one of the networks in RouterC goes down? - What is routerc s response of losing a network? - What is routerb s response of RouterC losing a network? - What is routera s response of RouterC losing a network?

12 * The following is the hint for the above question (- split horizon): * Which route will router uses to send packet from PC1 to PC2 if RIP is the routing protocol? (Uses the picture below) Which route will router uses to send packet from PC1 to PC2 if EIGRP is the routing protocol? (Uses the picture below) - Make sure you understand the concept but not just memorize the question. You will get a different picture at the chapter quiz. * What is the metric for RIP in R1 to the network /24?