Notes Odom, Chapter 14 Routing Protocol Concepts and Configuration Flashcards Set:

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1 EDTECH 552 (SP11) Susan Ferdon Notes Odom, Chapter 14 Routing Protocol Concepts and Configuration Flashcards Set: network route route metrics static route default route dynamic route routing protocol RIP EIGRP A data transmission path through one or more networks between two end nodes. The cost in time and resources to send a data packet over that route. A route that is manually configured on a router. Includes destination IP, subnet mask, and next-hop-ip (or outgoing interface). Route remains static/unchanged unless reconfigured. On a router, the route that is considered to match all packets that are not otherwise matched by some more specific route. A route that the router learns from neighboring routers. A set of messages and processes with which routers can exchange information about routes to reach subnets in a particular network. Examples of routing protocols include the Enhanced Interior Gateway Routing Protocol (EIGRP), the Open Shortest Path First (OSPF) protocol, and the Routing Information Protocol (RIP). Routing Information Protocol An Interior Gateway Protocol (IGP) that uses distance vector logic and router hop count as the metric. RIP Version 1 (RIP-1) has become unpopular, with RIP Version 2 (RIP-2) providing more features, including support for VLSM. Enhanced Interior Gateway Router Protocol EIGRP is an advanced distance-vector routing protocol, with optimizations to minimize both the routing instability incurred after topology changes, as well as the use of bandwidth and processing power in the router. The data EIGRP collects is stored in three tables: Neighbor Table, Topology Table, and Routing table. Routing information is

2 OSPF IS-IS administrative distance metric VLSM IGP EGP AS exchanged only upon the establishment of new neighbor adjacencies, after which only changes are sent. Open Shortest Path First An adaptive routing protocol for Internet Protocol (IP) networks which uses a link state routing algorithm and operates within a single autonomous system (AS). It gathers link state information from available routers and constructs a topology map of the network. The topology determines the routing table presented to the Internet Layer which makes routing decisions based solely on the destination IP address found in IP packets. Intermediate System to Intermediate System Routing Protocol An interior gateway protocol, designed for use within an administrative domain or network. IS-IS is a link-state routing protocol, operating by reliably flooding link state information throughout a network of routers. Each IS-IS router independently builds a database of the network's topology, and packets (datagrams) are forwarded, based on the computed ideal path, through the network to the destination. In Cisco routers, a means for one router to choose between multiple routes to reach the same subnet when those routes were learned by different routing protocols. The lower the administrative distance, the better the source of the routing information. A unit of measure used by routing protocol algorithms to determine the best route for traffic to use to reach a particular destination. Variable-length subnet masking The capability to specify a different subnet mask for the same Class A, B, or C network number on different subnets. VLSM can help optimize available address space. Interior Gateway Protocol A routing protocol that was designed and intended for use inside a single autonomous system. Exterior Gateway Protocol A routing protocol that was designed and intended for use between different autonomous systems. Autonomous System

3 BGP An internetwork in the administrative control of one organization, company, or governmental agency, inside which that organization typically runs an Interior Gateway Protocol (IGP). Border Gateway Protocol A protocol that is used to exchange routes between routers in different autonomous systems. It is an EGP. balanced hybrid A term that refers to a general type of routing protocol algorithm, the other two being distance vector and link state. The Enhanced Interior Gateway Routing Protocol (EIGRP) is the only routing protocol that Cisco classifies as using a balanced hybrid algorithm. classful routing protocol classless routing protocol convergence distance vector link-state routing update Does not transmit the mask information along with the subnet number, and therefore must consider Class A, B, and C network boundaries and perform autosummarization at those boundaries. Does not support VLSM. An inherent characteristic of a routing protocol, specifically that the routing protocol does send subnet masks in its routing updates, thereby removing any need to make assumptions about the addresses in a particular subnet or network, making it able to support VLSM and manual route summarization. The time required for routing protocols to react to changes in the network, removing bad routes and adding new, better routes so that the current best routes are in all the routers routing tables. The logic behind the behavior of some interior routing protocols, such as RIP. Distance vector routing algorithms call for each router to send its entire routing table in each update, but only to its neighbors. Distance vector routing algorithms can be prone to routing loops but are computationally simpler than linkstate routing algorithms. A classification of the underlying algorithm used in some routing protocols. Link-state protocols build a detailed database that lists links (subnets) and their state (up, down), from which the best routes can then be calculated. A generic reference to any routing protocol s messages in which it sends routing information to a neighbor.

4 CCNA Certification for Dummies --- BEST!! (The following is a combination of info from the textbook and Dummies book.) A network route is a data transmission path through one or more networks between two end nodes. More than one route can exist. The main purpose of a router is to find the best route to read a destination node. The best route is calculated through route metrics: the cost in time and resources to send a data packet over that route (Dummies, p. 593). There are three types of network routes: Static routes: Defined manually on a router they are static (unchanged) unless you reconfigure. o Advantages: Efficiency you can leave routing protocols disabled which saves bandwidth. Security you can filter routing data using firewalls and VPN to secure data no matter which path they travel on. o Disadvantages: Maintenance management overhead to update routes Accuracy if network changes and you don t update static routes you will have lost or delayed data. Scalability Large networks have hundreds or thousands of alternate routes too many to configure and maintain statically. Default routes: Default routes are static routes that you define for packets bound to a destination network that is not in any of the routing tables on your router. A default route is a data transmission path to that default outbound gateway in a network. o Default routes work best when only one path exists to a part of the network. o Without a default route, the router will discards packets that don t match the routing table. Dynamic routes: Routes that change over time. May be due to network topology and traffic updates, available bandwidth, and link state. o Advantages: Low maintenance routes are automatically updated, all you have to do is configure routing protocols on your routers. Accuracy Routing protocols keep track of network changes which means routers will send packets over the best possible routes.

5 Scalability in a large network it s a maintenance nightmare to define all routes statically. Routing protocols allow routers to communicate about routes they know, new routes they discover, and routes that become unavailable or overloaded. o Disadvantages: Overhead consumes bandwidth because they regularly send route update packets between routers. Connected and Static Routes Connected Routes A router adds routes to its routing table for the subnets connected to each of the router s interfaces - the router must have an IP address and mask configured on the interface (statically with the ip address command or dynamically using Dynamic Host Configuration Protocol [DHCP]) and both interface status codes must be up. In Example 14-1, the output of the show ip route command confirms that Albuquerque indeed added a route to all three subnets to its routing table. The output begins with a single-letter code legend, with C meaning connected. The output lists the mask in prefix notation by default. In cases when one mask is used throughout a single classful network in other words, static-length subnet masking (SLSM) is used the show ip route command output lists the mask on a heading line above the subnets of that classful network. Static Routes Static routes are best for LANs maintenance issues make static routes practically impossible for WAN/large networks. If a route changes, that change would have to be manually configured on each individual router. Configure static routes using the ip route command in global configuration mode. Syntax: ip route dest-ip subnet {next-hop-ip interface} o Dest-ip: IP address of the destination network. You are registering a static route to the destination network.

6 o Subnet: This is the subnet mask of the destination network; defines which part of address is network and which is host. o {next-hop interface}: IP gateway (router) through which you reach the destination network. Specify the IP address of the next hop or the outbound interface through which the router can reach the destination. Interface is used when it s a point-to-point serial link. o {} means you must specify something, (pipe) means choose one or the other of the options. To remove a static route use the usual no prefix with ip route command: no ip route dest-ip [subnet] {next-hop-ip interface}. You configure default routes using the same ip route command in global configuration mode. However, the IP address and subnet mask are which means match all packets - since the network is unknown. You can see all routes using show ip route command. To see only statically configured routes, use show ip route static. Telnet to a router and use ping commands to see which routes a router is able to connect to (Text, p. 444). When you troubleshoot this internetwork, you can use the extended ping command to act like you issued a ping from a computer on that subnet, without having to call a user and ask to enter a ping command for you on the PC. Routing Protocol Overview Routing protocols help routers learn routes by having each router advertise the routes it knows. Each router begins by knowing only connected routes. Then, each router sends messages, defined by the routing protocol, that list the routes. When a router hears a routing update message from another router, the router hearing the update learns about the subnets and adds routes to its routing table (Text, p. 448). Routing protocols exchange network, routes, and metric information between routers to help find optimal routes as fast as possible. Routers use the information provided by routing protocols to build their routing tables for each routed protocol to keep track of networks, paths to networks, and metrics associated with each route (Dummies, p. 598). The most widely used routing protocols are: Routing Information Protocol (RIP) Enhanced Interior Gateway Routing Protocol (EIGRP) Open Shortest Path First (OSPF)

7 Routing Decision Criteria Routers pick different network routes depending on various criteria. Some routes may be deemed faster by different routing protocols. Routers keep separate routing tables for each protocol. A route that is best now may not be best in a few minutes, depending on various criteria like traffic, available bandwidth, and link state. Routing tables keep track of networks, paths to networks, and metrics associated with each route. Routers consider two aspects when deciding which network routes are best at a given moment: o Administrative Distance How reliable is the information source that provided the data about the network route? o Routing Protocol Metrics What are the costs associated with each network route? Administrative Distance (AD) Routers learn about networks using various methods: o Directly connected AD = 0. Router learns about the network firsthand, because it connects to it. o Static route AD = 1. The router does not see the network, but it s been informed about its existence by a fairly reliable source (the static route). o Connected indirectly The router heard about it from another router (EIGRP, SOPF, RIP). Routers prefer sources with lower AD numbers. If the same routing protocol finds two different routes to the same destination and the AD is the same, other metrics are considered to decide which route to use. Routing Protocol Metrics (Dummies, p. 600) Each routing protocol calculates the efficiency (the cost) of a route differently. Whenever routing protocols contradict each other, the one with the lowest AD is preferred. If the same routing protocol finds two (or more) routes to the same destination, specific decision criteria are used: o Hop count the number of routers that need to be transversed (prefer few hops because there is delay at every hop). RIP uses hop count metric to choose network routes. o Bandwidth prefer routes with larger bandwidth; very likely packets will arrive faster. EIGRP uses bandwidth metric to choose network routes.

8 o Delay Total delay calculated on processing delay, queuing delay, transmission delay and propagation delay (EIGRP). o Reliability Percentage of time the route is available (EIGRP) o Load Bandwidth consumed by current traffic on a given route; the difference between total bandwidth and available bandwidth of the route (EIGRP). o Maximum Transmission Unit (MTU) The size, in bytes, of each data packet. The higher the MTU, the more data can be transferred at once (EIGRP). o Cost Calculated based on the bandwidth of a network route; 10 8 /bandwidth (OSPF). Routing Methods (Dummies, p. 602) Routing protocols use different methods to exchange the info that helps routers build their routing tables. Distance vector routing: o Build routing tables based on route distance. o Exchange and combine their routing table with their neighbors (called convergence). o Neighbor routers trust each other s route information, and they relay the combined information farther. o Routing tables are combined and relayed to all routers in the network. o Because DV routing protocols combine the routing tables of all routers and propagate them to all neighbors, the convergence process can be very long in larger networks. o Distance vector routing can cause routing loops so various features are used to avoid routing loops: Maximum hop count never takes route that exceeds certain number of hops (looping). Split horizon prevents route from be advertised back to its advertiser. Route poisoning changes hop count for route that become unreachable, which disables a route quickly. Poison reverse breaks the split horizon rule ensuring that all neighbors receive route down message as quickly as possible. Hold-down timer prevents router from accepting updates about a router for a certain amount of time if that was reported as down. Triggered update allows routers to update each other as soon as a change occurs, rather than waiting for scheduled update to be exchanged. o Best suited for access or distribution layer routers.

9 o RIP and IGRP (replaced by EIGRP) are distance vector routing protocols. Link-state routing: o Build their routing tables independently based on route updates they receive from their neighbors. o Do not merge the routing tables of neighbor routers. o Enable routers to have clear image of their neighbors, network topology, and routes to neighbors and beyond. o OSPF uses link-state routing. Hybrid routing: o Have both distance vector and link-state characteristics. o Like distance vector protocols hybrid routing protocols use distance to evaluate quality of routes. hybrid routing protocols send route updates that contain the whole routing table o Like link-state protocols hybrid routing protocols use other metrics in addition to distance to evaluate the quality of routes. hybrid routing protocols only exchange hello messages initially so convergence time is faster than distance vector protocols. hybrid routing protocols send updates only when routes change. o Hybrid routing protocols are well-suited for core layer, distribution layer, and even access layer routers. o EIGRP is considered a hybrid routing protocol. RIP-2 Basic Concepts (p. 449) Routers using RIP-2 advertise a small amount of simple information about each subnet to their neighbors. Their neighbors in turn advertise the information to their neighbors, and so on, until all routers have learned the information. RIP routers send periodic routing updates about every 30 seconds by default. When something changes, the routers will react and converge to use the then-best working routes. Figure 14-3 (p. 449) shows RIP-2 advertising subnet number, mask, and metric to its neighbors. Comparing and Contrasting IP Routing Protocols (p. 450) Important considerations: o Is it a public standards (defined in RFCs) or Cisco proprietary?

10 o Does the routing protocol support variable-length subnet masking (VLSM)? Interior and Exterior Routing Protocols (p. 451) Two types: o Interior Gateway Protocol (IGP): A routing protocol that was designed and intended for use inside a single autonomous system. o Exterior Gateway Protocol (EGP): A routing protocol that was designed and intended for use between different autonomous systems. An autonomous system is an internetwork under the administrative control of a single organization. Each autonomous system can be assigned a number, called an autonomous system number (ASN). Like public IP addresses, the Internet Corporation for Assigned Network Numbers (ICANN) controls the worldwide rights to assign ASNs. By assigning each autonomous organization an ASN, Border Gateway Protocol (BGP is an EGP) can ensure that packets do not loop around the global Internet by making sure that packets do not pass through the same autonomous system twice. Metrics give an objective number to the goodness of each route. The lower the metric, the better the route. Figure 14-5 compares two routes RIP/hop count and EIRGP/bandwidth. Autosummarization and Manual Summarization (p. 454) Routers generally perform routing (forwarding) more quickly with smaller routing tables, and less quickly with larger routing tables. Route summarization helps shorten the routing table while retaining all the needed routes in the network.

11 Manual summarization gives the network engineer a great deal of control and flexibility, allowing the engineer to choose what summary routes to advertise, instead of just being able to summarize with a classful network. Classless and Classful Routing Protocols (p. 454) Classful routing protocol: o must consider the Class A, B, or C network number that a subnet resides in when performing some of its tasks. o does NOT support VLSM. o does NOT send subnet mask in routing updates. o does NOT support manual route summarization. Classless routing protocols do not need to consider class rules. o DOES support VLSM. o DOES send subnet mask in routing updates. o DOES support manual route summarization. The processes used by routing protocols to recognize the changes, to figure out the now-best routes to each subnet, and to change all the routers routing tables, is called convergence. Some routing protocols converge more quickly than others. Later-defined IGPs typically support some kind of authentication as a means of mitigating possible DoS attacks.

12 Configuring and Verifying RIP-2 (p. 456) Three-step process: o Step 1 - Use the router rip configuration command to move into RIP configuration mode. o Step 2 - Use the version 2 RIP subcommand to tell the router to use RIP Version 2 exclusively. o Step 3 - Use one or more network net-number RIP subcommands to enable RIP on the correct interfaces. Each RIP network command enables RIP on a set of interfaces. The RIP network command only uses a classful network number as its one parameter. For any of the router s interface IP addresses in that entire classful network, the router does the following three things: o The router multicasts routing updates to a reserved IP multicast IP address, o The router listens for incoming updates on that same interface. o The router advertises about the subnet connected to the interface. Sample RIP configuration on page 457.

13 RIP configuration does not provide a way to enable RIP on only some interfaces so the network must be configured then use the passiveinterface type-number RIP subcommand to stop sending RIP updates out that interface. IOS includes three primary show commands to confirm how well RIP- 2 is working (detailed example begins on p. 459). Of particular importance for real-life troubleshooting and for the exam, focus on both the version information and the routing information sources. If you forget to configure the version 2 command on one router, that router will send only RIP-1 updates by default, and the column labeled Send would list a 1 instead of a 2. The other routers, only listening for Version 2 updates, could not learn routes from this router. (Text goes over Administrative Distance, see notes from Dummies book, above.) Examining RIP Messages with debug (p. 464) The best way to understand whether RIP is doing its job is to use the debug ip rip command. This command enables a debug option that tells the router to generate log messages each time the router sends and receives a RIP update. Example 14-9 shows the output generated by the debug ip rip command on the Albuquerque router, based on Figure Note that to see these messages, the user needs to be connected to the console of the router, or use the terminal monitor privileged mode EXEC command if using Telnet or SSH to connect to the router. A close examination of the number of subnets in each routing update (Example 14-9) shows that the routers do not advertise all routes in the updates. The reason has to do with the theory behind RIP,

14 specifically a feature called split horizon. This loop-avoidance feature limits which subnets are advertised in each update to help avoid some forwarding loops. Before using the debug command, look at the router s CPU utilization with the show process command. On routers with a higher CPU utilization, generally above 30 to 40 percent, be very cautious when enabling debug options, as this may drive the CPU to the point of impacting packet forwarding. To make the router generate time stamps, you need to configure the service timestamps global configuration command.

15 Do I Know This Already Quiz, Chapter 14 - pp TOPIC Q# 1 st Try 2 nd Try Answer Connected and Static 1 B, C A, C Routes 2 A, C, D A 3 A A, B 4 E, F Routing Protocol Overview B, D, E, 5 B F 6 B, D, E D, E, F A, D, G, A, D, E, 7 I H Configuring and Verifying 8 F A RIP-2 9 D, E, F B 10 B, C, F B, C Q1: Which of the following must be true for a static route to be installed in a router s IP routing table? a. The outgoing interface associated with the route must be in an up and up state. b. The router must receive a routing update from a neighboring router. c. The ip route command must be added to the configuration. d. The outgoing interface s ip address command must use the special keyword. Answer: A, C Explanation: Typo I really meant A. B is not correct since configuring static routes do not rely on learning routes from neighbors (that would be dynamic routing). Q2: Which of the following commands correctly configures a static route? a. ip route b. ip route serial 0 c. ip route / d. ip route /24 serial 0 Answer: A Explanation: Commands for static route include destination IP, subnet mask, and next-hop-ip interface. B is not correct because there is no subnet mask. C and D are not correct because it must be dotted decimal format.

16 Q3: Which of the following routing protocols are considered to use distance vector logic? a. RIP b. IGRP c. EIGRP d. OSPF Answer: A and B Explanation: I forgot about IGRP. The Dummies books says that isn t used anymore it was replaced by EIGRP. Q5: Which of the following routing protocols support VLSM? a. RIP b. RIP-2 c. IGRP d. EIGRP e. OSPF f. Integrated IS-IS Answer: B, D, E and F Explanation: A is not correct RIP does not send subnet mask so variablelength subnet mask would not be supported. C is not correct IGRP is also old, not supported. Basically, new ones support VLSM old ones don t. Q6: Which of the following routing protocols are considered to be capable of converging quickly? a. RIP b. RIP-2 c. IGRP d. EIGRP e. OSPF f. Integrated IS-IS Answer: D, E and F Explanation: I said B, D and F. B is not correct both RIP and RIP-2 send the whole routing table so convergence won t be quick. Hybrid and link-state

17 don t merge tables, so convergence is faster that would be EIGRP, OSPF and Integrated IS-IS. Q7: Router1 has interfaces with addresses and Router2, connected to Router1 over a serial link, has interfaces with addresses and Which of the following commands would be part of a complete RIP Version 2 configuration on Router2, with which Router2 advertises out all interfaces, and about all routes? a. router rip b. router rip 3 c. network d. version 2 e. network f. network g. network h. network i. network Answer: A, D, E, H Explanation: I said A, D, G, I. A is correct because we are configuring with RIP routing protocol. D is correct because we are using RIP-2, not RIP. Other answers were wrong because I misread the question I thought we were configuring Router 1, so network numbers for that router (answers G and I) would not be used. We are configuring Router 2, so static routes to Router 1 addresses would be configured. **Is H a mistake? is on Router 2. Q8: Which of the following network commands, following a router rip command, would cause RIP to send updates out two interfaces whose IP addresses are and , mask ? a. network b. network c. network d. network e. network 10 f. You cannot do this with only one network command. Answer: A Explanation: I said F because I thought you had to do the thing where you configure RIP for the whole router then disable some of the interfaces. A is correct because that is the address for the network that the two interfaces

18 are part of. B and C are not correct because you can t put two IP addresses in the same command plus using the IP address for the entire network covers both bases with one command. Answer E is not correct 10 is not a valid address. Q9: What command(s) list(s) information identifying the neighboring routers that are sending routing information to a particular router? a. show ip b. show ip protocol c. show ip routing-protocols d. show ip route e. show ip route neighbor f. show ip route received Answer: B Explanation: I said D, E and F. Per Table 14-5, show ip protocol lists information about the RIP configuration, plus the IP addresses of neighboring RIP routers from which the local router has learned routes. D, E, and F are not correct show ip route command shows learned routes but not IP addresses from which those routes were learned. I haven t found any documentation that shows that E or F use correct syntax. Q10: Review the snippet from a show ip route command on a router: R [120/1] via , 00:00:13, Serial0/0/1 Which of the following statements are true regarding this output? a. The administrative distance is 1. b. The administrative distance is 120. c. The metric is 1. d. The metric is not listed. e. The router added this route to the routing table 13 seconds ago. f. The router must wait 13 seconds before advertising this route again. Answer: B and C Explanation: I said B, C and F. F is not correct - the time listed is the amount of time since the router last heard about this route.