354 Chapter 9 BGP Scalability and Advanced Features 5. If multiple ISPs are connected to your network, BGP can load balance over up to how many links? A. Eight B. Thirty-two C. Six D. One 6. You can define communities using which type of filters? A. Standard access lists B. Route maps C. Prefix lists D. Extended access lists 7. Which of the following can be used to avoid creating a full-mesh net- work? (Choose all that apply.) A. Confederations B. Route maps C. Prefix lists D. Route reflectors 8. Which of the following commands shows the configured peer BGP routers and the current connection state? A. show ip bgp all B. show cdp bgp neighbors C. show running-config D. show ip bgp neighbors Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com Review Questions 355 9. What router command mode is used to start BGP using the router bgp 100 command? A. User mode B. Privilege mode C. Global Configuration mode D. Interface Configuration mode E. Route Map Configuration mode 10. What are two advantages of prefix lists over distribute lists? A. Less CPU usage B. Easy to configure C. Affect advertised routes and data coming into an interface D. Can be configured on individual interfaces 11. Which of the following is not a way of managing routes advertised by BGP routers? A. Using route maps B. Using prefix lists C. Using distribute lists D. Using path filters E. Using redistribution lists 12. You can lengthen the AS-PATH length by doing which of the following? A. Add a new value using the ip bgp as-path value command. B. Add false AS numbers C. Add a new value using the set as-path extended command. D. Use the bgp dampening command. Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com 356 Chapter 9 BGP Scalability and Advanced Features 13. Statements in distribute lists are processed in which order? (Choose all that apply.) A. The order in which they were entered B. From the top down C. The order given by the sequence number D. All of the above 14. When configuring a prefix list, if the seq syntax is not used, in what sequence are numbers assigned and in what increment? A. 1 (1,2,3…) B. 5 (10,15,20…) C. 10 (10,20,30…) D. 25 (25,50,75…) 15. A BGP router not participating in a route reflector cluster is called which of the following? A. Non-cluster client B. Non-BGP router C. Non-client D. Non-iBGP client 16. The COMMUNITIES attribute can contain a value in what range of numbers? A. 1 to 1012 B. 1 to 255 C. 0 to 512 D. 1 to 4,294,967,200 Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com Review Questions 357 17. Which of the following is not used in confederations? A. iBGP B. eBGP C. Sub-ASes D. Sequence numbers E. Confederation identifier 18. Which command can be used to disable sequence numbering when creating prefix lists? A. ip bgp prefix-list sequence-number disable B. no ip prefix-list sequence-number C. disable ip bgp prefix-list sequence-number D. no ip prefix-list 19. Which of the following ranges of numbers can be assigned to a BGP distribute list? A. 299 to 399 B. 1 to 200 C. 1 to 199 D. 1 to 2,000 20. When creating prefix lists, which of the following are optional syntaxes? A. list-name B. ge C. le D. seq Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com 358 Chapter 9 BGP Scalability and Advanced Features Answers to Written Lab 1. The set command 2. Privileged mode 3. Peer group 4. neighbor group6 peer-group 5. Basic, Medium, and Full 6. ip route 0.0.0.0 0.0.0.0 serial 0 7. ip route 0.0.0.0 0.0.0.0 serial 0 200 8. clear ip peer-group group3 9. bgp dampening 10. Route Map Configuration mode displayed on the router prompt as Router(config-route-map)# Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com Answers to Review Questions 359 Answers to Review Questions 1. A. The least restrictive statements should be placed at the top of an access list. This means that if the last statement is the implicit deny all, then the permit statements should be first unless you want to deny a subset of what was permitted. A good rule to remember is that the most specific statements should be at the top. 2. D. Route summarization reduces the number of entries found in the routing table, creating a single summarized route for all the entries in the routing table for networks residing out a single interface. 3. A, B, D. A prefix list can be reconfigured with new statements, or you can delete statements at any time as long as they are numbered with sequence numbers. The set command is used to tell the router what to do when a match is made in a route map. 4. D. A route reflector is used to manage larger networks. A route reflec- tor should be peered with other route reflectors, its own route reflector clients, and those routers not participating in a route reflector cluster. 5. C. You can have up to six physical links to ISPs and use those links to send data traffic back and forth from your network to your ISP’s net- work. This effectively allows you to not only have redundant links, but to use those redundant links to load balance your traffic. 6. B. The COMMUNITIES attribute can be used in route maps. The COMMUNITIES attribute identifies a common set of BGP routers participating in a community. 7. A, D. Confederations and route reflectors can both be configured to avoid creating a full-mesh network where the neighbors command is used excessively. 8. D. The show bgp neighbors command shows the configured BGP peers and the current connection status. 9. C. The router bgp command is used in the Global Configuration mode. Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com 360 Chapter 9 BGP Scalability and Advanced Features 10. A, B. Prefix lists use considerably less CPU space and are much easier to configure than access lists. They cannot affect advertised routes coming into an interface and are configured globally on a router, not on each interface. 11. E. There is no such thing as a redistribution list using BGP. The other ways listed are all valid ways of manipulating routes advertised by BGP. 12. B. You can increase the AS-PATH length by adding false AS numbers. Although the ip bgp as-path value command and the set as- path extended command appear convincing enough, they are not real commands. The bgp dampening command is used by BGP to set a hold time before a route can be re-advertised after route flapping. 13. A, B. Statements are entered in a distribute list by configuring an access list. The statements are processed in the order in which they were entered and from the top down. Sequence numbers are not used in distribute lists. 14. B. Sequence numbers are assigned in increments of five when no sequence number was assigned when the prefix list statements were configured. 15. C. BGP routers not participating in a route reflector client are called non-client routers. 16. D. The COMMUNITIES attribute value can be any number between 1 and 4,294,967,200. 17. D. The sequence number is used in prefix lists. Confederations use iBGP on routers in sub-ASes and then use eBGP to connect the sub- ASes. 18. B. The no ip prefix-list sequence-number command is used to disable sequence numbering for prefix lists. The only other real com- mand is the no ip prefix-list command, which is used to delete a prefix list. Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com Answers to Review Questions 361 19. C. This is sort of a trick question. The reason is that distribute lists are created using access lists. IP standard access lists are numbered 1 to 99, and extended access lists are numbered 100 to 199. 20. B, C, D. The prefix-list command is followed by the list-name syntax. The ge, le, and seq syntaxes are all optional and not required. Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com Chapter 10 Route Optimization THE CCNP ROUTING EXAM TOPICS COVERED IN THIS CHAPTER ARE AS FOLLOWS: Show the need for route redistribution Review the metrics of commonly used routing protocols Illustrate how to redistribute routing protocols, including RIP, OSPF, IGRP, and EIGRP Learn how to verify and troubleshoot route redistribution Explore how to fine-tune route redistribution through the use of access lists and route maps Recognize the benefits of policy routing Detail how to direct traffic flows through the use of policy routing Configure route maps to control traffic flows Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com In this chapter, we will discuss how to take networks running dif- ferent routing protocols and allow them to exchange routing information, through a process called route redistribution. One of the challenges of route redistribution is that many routing protocols use different metrics. To over- come this challenge, we will show you how to set default metrics for various routing protocols. After examining several redistribution examples, we will review commands for verifying and troubleshooting route redistribution. We will discuss many advanced route-manipulation techniques, including setting metrics on a protocol-by-protocol basis and setting metrics for spe- cific routes. We’ll introduce the distribute-list feature as a tool for fil- tering the receiving or advertising of routes, and we’ll show the virtual interface Null0 to be an efficient way of discarding packets destined for spec- ified networks. We will also detail how to redistribute static and connected routes. In addition, we’ll introduce the powerful features of route maps. Route Redistribution We have previously discussed various routing protocols available on Cisco routers. Some of the more common routing protocols are RIP, IGRP, EIGRP, and OSPF. However, we have not considered what happens when we interconnect networks that are running differing routing protocols. To illustrate this situation, let’s consider the implications of when two busi- nesses (or divisions within the same business) merge. Let’s say that Company A had a network infrastructure that used the Cisco proprietary EIGRP pro- tocol, as shown in Figure 10.1. Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com [...]... (e.g., classless routing protocols), and some routing protocols do not include subnet information (e.g., classful routing protocols) Therefore, to better understand how we redistribute one routing protocol into another, let’s first review some characteristics of various routing protocols Routing Protocol Metrics In this section, we will discuss the various routing protocols and metrics used to calculate... of mixed routing protocols is route redistribution The reason that route redistribution does not happen automatically between diverse routing protocols is that the protocols have different methods of representing the desirability of a route This desirability is called a metric Also, some routing protocols include subnet information (prefix information) within routing updates (e.g., classless routing. .. This command displays what routes the router has learned and by which routing protocol it learned them You can verify that all the networks are in the routing table show ip protocols This command displays the IP routing protocols configured on the router and shows what each routing process is redistributing Let’s look at an example: Routing Protocol is “ospf 1” Sending updates every 0 seconds Invalid... However, unlike RIP, OSPF is a classless routing protocol, which means that it includes subnet information (prefix information) in its routing updates OSPF is typically the fastest converging routing protocol for IP However, we have found that EIGRP can give it a run for the money in smaller networks in regards to convergence times IGRP IGRP (Internet Gateway Routing Protocol) is a Cisco proprietary... a tiebreaker The other important characteristic of RIP that we are considering is that RIP is a classful routing protocol This means that the subnet mask (prefix information) is not sent with the route updates as it is with classless routing protocols RIP cannot effectively work with classless routing protocols like EIGRP and OSPF because of this reason However, RIP version 2 sends prefix information... to the remote network, then the metric of a routing protocol is used to determine the best path If the metrics are the same, the routing Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com Route Redistribution 367 protocol will perform load balancing over the available routes It is important that you understand the default administrative distance of each routing protocol and the metrics used so that... Route Optimization ! router rip which enables the RIP routing process redistribute eigrp 10 which tells the router to take routes learned via EIGRP AS 10 and readvertise them via RIP network 8.0.0.0 where network is the network that is part of the RIP routing process default-metric 3 where 3 is to be used as the default metric (hop count) when other routing protocols are injected into RIP At this point,... IP RIP RIP (Routing Information Protocol) uses a simple metric called the hop count The hop count for a network is simply the number of routers that a packet must pass through to reach that network The hop-count metric does not take into account such things as the speed or reliability of a link, just the number of hops In this way, RIP is similar to the AppleTalk routing protocol of RTMP (Routing Table... will not show up in the routing table This situation can occur when you forget to set a protocol’s default metric Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com 376 Chapter 10 Route Optimization Advanced Redistribution Our redistribution examples up to this point have set the default metric for a particular routing protocol That metric is then used every time another routing protocol is redistributed... that particular routing protocol Also, in our examples, all the routes have been redistributed; that is, we have not been filtering the content of our routing updates We will now examine how to control redistribution with a higher degree of granularity For example, we may want RIP to apply one metric to OSPF and another metric to IGRP, as these products are redistributed into the RIP routing process . called a metric. Also, some routing protocols include subnet information (prefix information) within routing updates (e.g., classless routing protocols), and some routing protocols do not include. classful routing protocols). Therefore, to better understand how we redistribute one routing protocol into another, let’s first review some characteristics of vari- ous routing protocols. Routing. CA www.sybex.com Chapter 10 Route Optimization THE CCNP ROUTING EXAM TOPICS COVERED IN THIS CHAPTER ARE AS FOLLOWS: Show the need for route redistribution Review the metrics of commonly used routing protocols Illustrate