416 Appendix A Practice Exam 12. C. EIGRP routes have a default administrative distance of 90. 13. B, D. The show ip bgp neighbor command displays all the adver- tised routes, and the show ip bgp command looks at all the connections. 14. D. If you write out the networks 172.16.100.0/24 and 172.16.106.0/ 24 in binary and see how many leading bits that they have in common, you will find that the first 20 bits are the same for both networks. If you then convert these 20 bits back into decimal, you will have the address of the summarized route. 15. A and B. In an OSPF network, there must always be a backbone area, which is numbered as Area 0. If a router has any of its interfaces connected to Area 0, that router is said to be a backbone router. 16. A, B, C, E, F. Access lists, snapshot routing, compression tech- niques, Dial-on-Demand Routing (DDR), and incremental updates all can help reduce bandwidth usage. 17. A. The show ip protocols command will display such information as redistribution parameters. 18. B. The command no auto-summary is a router- configuration command that disables the automatic summarization of routes. 19. C. Classless routing protocols send prefix routing information with each update. 20. B. The other options are invalid syntax. 21. D. The show bgp neighbors command shows the configured BGP peers and the current connection status as shown above. 22. C. A transit AS is an AS through which data from one AS must travel to get to another AS. Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com Answers to Practice Exam 417 23. B. The answer here can be tricky. There are six initialization steps, but not all of them are always seen. Many times the Loading phase is not necessary between the Exchange state and the Full state. 24. B. Route summarization is most effective when used with contiguous address space, because contiguous address space tends to have the most higher-order bits in common. 25. C. The init state is simply the state of receiving Hello packets on the interface; no adjacencies or other information have been exchanged at this point. 26. B. Traffic sent to the virtual interface Null0 is discarded. 27. C, D. IP unnumbered is not supported on X.25 or SMDS networks. Since the serial interface has no IP number, you will not be able to ping the interface to see if it is up. However, you can determine the interface status with SNMP. Also, IP security options are not supported on an IP unnumbered interface. 28. D. Classful routing protocols send no subnet mask information with the routing updates, so all devices on the network must use the same subnet mask. 29. A. The area-id parameter in the area area-id virtual-link router-id command refers to the ID of the transit area. The transit area connects the backbone area to the area requiring the virtual link. 30. D. The show bgp neighbors command shows the configured BGP peers and the current connection status. 31. C, D, E, F. Alternate path routing, which provides redundancy and load balancing, along with snapshot routing, tunneling, and dial backup all provide stability and availability in an internetwork. 32. C. Both switches and bridges break up collision domains but are one large broadcast domain by default. All broadcasts are forwarded to all network segments with a bridge or switch. Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com 418 Appendix A Practice Exam 33. B. The EIGRP process number is always the number assigned to an autonomous system. 34. B. Static routes have a default administrative distance of 1. 35. D. The commands router bgp 100 and neighbor 10.1.1.1 remote-as 200 configure BGP with an external BGP neighbor. 36. A, B, C. Slow convergence, non-optimal routes, and routing loops are all problems that can occur by using route redistribution. 37. D. Passive interfaces are used for such interfaces as BRI where you do not want to have routing updates sent out the interface. If routing updates were sent out of a BRI interface, then the interface would never disconnect. 38. B. The 1 refers to the access list against which the match command is testing traffic. 39. D. If you write out 255.255.255.224 in binary, you will find that the first 27 bits are ones, and the remaining five bits are zeros. Therefore, we say that it is a /27. 40. A, B, C. The smooth round-trip timer (SRTT), the retransmission timer (RTO), and the hold timer are all used by the neighbor table to track its neighboring routers. The Time To Live and Stop timers are not used by the EIGRP neighbor table. 41. C. Border Gateway Protocol can load balance connections with as many as six different ISPs. 42. D. Port 179 is used by BGP to establish a session with another BGP peer. Ports 20 and 21 are used by FTP, and port 23 is used by Telnet. 43. D. The bgp dampening command is used by BGP to set a hold time before a route can be re-advertised after route flapping. 44. D. The Weight attribute is a Cisco proprietary attribute used as a metric only in Cisco implementations of BGPv4. Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com Practice Exam 419 45. E. OSPF has an administrative distance of 110. 46. A. This status could result from an interface being down, but the spe- cific OSPF definition is the lack of Hello packets received from the neighbor. 47. A. The OPEN message type is used to establish a connection between BGP peers and to negotiate the hold time. The UPDATE message type is used to advertise topology updates and changes. The NOTIFICA- TION message type is used to advertise errors. The KEEP- ALIVE message type is sent to keep a session active when no UPDATE messages are exchanged during the established hold time. 48. A. Route summarization is used to send fewer route entries in an update. This can reduce the routing table entries. 49. C. The area area-id stub no-summary IOS router configuration command is used to configure a router as totally stubby for the spec- ified area. Remember that by becoming totally stubby, a router stops receiving summary Link State Advertisements. 50. A, B, C. The valid BGP show commands listed above are show ip bgp, show ip bgp paths, and show ip bgp summary. The show ip bgp command displays the BGP routing table. The show ip bgp paths command displays all the router’s known BGP paths. The show ip bgp summary command tells you the status on every BGP connec- tion. The other two commands are not valid. Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com Appendix B Commands in This Study Guide Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com The following is a compilation of the commands listed in the “Commands Used in This Chapter” sections, along with an explanation for each command: Command Description Chapter aggregate-address Allows you to configure aggregate routes in BGP and CIDR addressing. 8 bgp default local- preference Allows you to assign a Local Preference attribute value in the range of 0 to 4,294,967,295. Higher values are preferred over lower values. 8 clear ip bgp Allows you to clear all or an identified set of routes from the BGP table. 8 debug ip bgp dampening Displays BGP dampening events as they occur. 8 debug ip bgp events Displays all BGP events as they occur. 8 debug ip bgp keepalives Displays all events related to BGP keepalive packets. 8 Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com Commands in This Study Guide 423 Command Description Chapter debug ip bgp updates Displays information on all BGP update packets. 8 distance When multiple protocols are running, this command allows a distance value from 1 to 255 to decide which path is the best. The lowest value wins. 6 ip unnumbered Allows serial interfaces to borrow an IP number from another router interface (which may or may not be specified), so that it can joint two contiguous address spaces. 3 neighbors This command has many syntaxes that allow you to identify the internal and external neighbors and assign different metrics to each. 8 network Identifies the networks and masks associated with the local router. 8 no auto-summary Used to disable the automatic route summarization performed by various classless routing protocols, such as RIPv2 and EIGRP. 3 no synchronization Allows you to turn off synchronization between the IGPs and BGP for faster convergence. 8 passive-interface interface-type interface-number Identifies interfaces that do not participate in EIGRP updates. 6 Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com 424 Appendix B Commands in This Study Guide Command Description Chapter router bgp Begins the BGP process and identifies the local ASN. 8 router eigrp Starts EIGRP processes on a router. 6 show ip bgp cidr-only Displays classless routes. 8 show ip bgp community Used to display routes belonging to the specified community. 8 show ip bgp filter-list Displays AS path lists. 8 show ip bgp paths Displays all path information for the local router. 8 show ip bgp peer-group Provides information on the members of the specified peer group. 8 show ip bgp summary Shows the status of all BGP connections. 8 show ip eigrp events Shows a log of EIGRP events. These are routes being added to or removed from the routing table. 6 show ip eigrp neighbors Shows directly connected EIGRP-enabled routers. 6 show ip eigrp topology Shows entries in the EIGRP topology table. 6 show ip eigrp traffic Shows the packet count for EIGRP packets sent and received. 6 show ip protocols Shows information about the active protocol sessions. 6 Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com Commands in This Study Guide 425 Command Description Chapter show ip route eigrp Shows all EIGRP neighbors. 6 variance Assigns a weight to each feasible successor. 6 Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com Appendix C Route Summarization Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com [...]... networks grows, so does the size of your route topology and routing tables Unfortunately, this large amount of information causes more CPU processes to occur and requires more physical memory on the router If something isn’t done about the size of the collection of information contained in the routing tables, your router will be advertising routing information that may be unnecessary to advertise Summarization... Update-based Routing Protocol: A technique for encapsulating AppleTalk traffic in the header of a foreign protocol that allows the connection of at least two noncontiguous AppleTalk internetworks through a foreign network (such as TCP/IP) to create an AppleTalk WAN The connection made is called an AURP tunnel By exchanging routing information between exterior routers, the AURP maintains routing tables... routes (Type IA) Routes that exist in the internal autonomous system but not in the router’s configured area External routes (Types E1 and E2) Routes that exchange routing information between autonomous systems Configured areas help divide shared routing information Area Border Routers (ABR) advertise IA routers from one area to another area Route Summarization for EIGRP E IGRP does not build the same hierarchy... address mapping adjacency The relationship made between defined neighboring routers and end nodes, using a common media segment, to exchange routing information administrative distance A number between 0 and 225 that expresses the value of trustworthiness of a routing information source The lower the number, the higher the integrity rating Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com Glossary... advertising routing information that may be unnecessary to advertise Summarization provides an excellent way to reduce the size of the topology and routing tables and significantly reduce the load on the router Summarization provides a way to aggregate routing information, summarize the known routes, and reduce the lines in the IGP tables If summarization doesn’t occur, every route—including those... that sets the duplex of a switch or hub port automatically automatic call reconnect A function that enables automatic call rerouting away from a failed trunk line autonomous confederation A collection of self-governed systems that depend more on their own network accessibility and routing information than on information received from other systems or groups autonomous switching The ability of Cisco routers... may ask higherlevel protocols to take necessary flow control measures Compare with: FECN BGP4 BGP Version 4: Version 4 of the interdomain routing protocol most commonly used on the Internet BGP4 supports CIDR and uses routecounting mechanisms to decrease the size of routing tables See also: CIDR bidirectional shared tree A method of shared tree multicast forwarding This method allows group members to... want to advertise You can also use the ip route command to create a static route The static route is then redistributed into BGP Redistribution occurs when a router uses different protocols to advertise routing information received between the protocols BGP considers a static route to be a protocol Static route information is advertised to BGP The third way to create a static route is to redistribute... (routes learned through an IGP) into BGP In Chapter 8 we learned the commands to enable this; however, Cisco does not recommend this approach because of convergence issues and the possibility of introducing routing loops into the network Convergence is the time it takes for the network to recover from a change in the network’s topology Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com Glossary Copyright... known as a “network access server,” it is a communications process connecting asynchronous devices to a LAN or WAN through network and terminal emulation software, providing synchronous or asynchronous routing of supported protocols Copyright ©2001 SYBEX , Inc., Alameda, CA www.sybex.com 436 Glossary acknowledgment Verification sent from one network device to another signifying that an event has occurred . the routing tables, your router will be advertis- ing routing information that may be unnecessary to advertise. Summarization provides an excellent way to reduce the size of the topol- ogy and routing. router- configuration command that disables the automatic summarization of routes. 19. C. Classless routing protocols send prefix routing information with each update. 20. B. The other options are invalid syntax. 21 are not supported on an IP unnumbered interface. 28. D. Classful routing protocols send no subnet mask information with the routing updates, so all devices on the network must use the same subnet