Answer Key Explanations | CCNP BSCI Exam Cram 2 (Exam Cram 642-801)


Question 1	Answer B is correct. The Core layer must feature the fastest and most efficient transmissions of data between other divisions of the network. As such, this layer often features the circuits with the largest bandwidth and often implements redundancy mechanisms. Answer A is incorrect because the Distribution layer is the consolidation point for the various Access layers in the hierarchical design. Answer C is incorrect because the Access layer is the entry point onto the network for end station systems and servers. Sometimes the Access layer is referred to as the Desktop layer. Answer D is incorrect because in the classic hierarchical network design from Cisco, there is no Workgroup layer.

Question 2	Answer B is correct. Administrative Distance is forced to 200. You can force the administrative distance used for a static route by setting the value in the `ip route` command. Doing so enables you to create a floating static route that is used as a backup route in the event the dynamic routing protocol fails to provide the necessary information. Answer A is incorrect because the metric value is not forced in the `ip route` command. Answer C is incorrect because this command does not specify the amount of time the route stays in the routing table. Answer D is incorrect because this value cannot designate the number of sessions that may use the route.

Question 3	Answer D is correct. Static routes are a heavy administrative task. The use of static routes in your enterprise network typically increases the administrative overhead required to maintain the network. As the network changes, you must manipulate the static routes manually. Answer A is incorrect because resource shortages are in fact a valid reason for the creation of static routes. Many routers do not possess enough CPU or memory to be wasteful . Answer B is incorrect because static routes also enable an administrator to have absolute control over the flow of traffic in the network, more so than dynamic routing. Answer C is incorrect because the use of static routes enables the administrator to have remote networks appear as if they are directly connected.

Question 4	Answer A is correct because RIP and IGRP use only major classful networks to determine the interfaces participating in the protocol. Answer C is also correct because integrated IS-IS does not use a `network` statement. Interface configuration mode is used to configure interfaces participating in the IS-IS routing process. Answer B is incorrect because BGP is the only dynamic routing protocol that uses the `network` statement to indicate an advertisement for the listed network. Answer D is incorrect because EIGRP and OSPF ”not IGRP and OSPF ”allow the specification of a wildcard mask.

Question 5	Answer B is correct because ODR is used in hub and spoke environments: Spoke routers send information to the hub and the hub sends default route information the spokes . ODR is appropriate only within a hub and spoke topology. In this design, the stub routers use CDP to send IP prefixes to the hub router. Answer D is also correct because the hub router sends default routes to the spoke routers. Answer A is incorrect because CDP does carry subnet mask information; therefore ODR is a classless routing technology. Answer C is incorrect because spoke routers do not send default routes ”they receive default routes from the hub router.

Question 6	Answer B is correct because the hub router needs the `router odr` global configuration command. Also answer D is correct because the spoke routers must feature CDP on the links between the spoke routers and the hub router. Answer A is incorrect because all routers participating in ODR do not require the `router odr` global configuration command. Answer C is incorrect because only the hub router requires default routes. The spoke routers do not need default routes configured; these routes are automatically injected from the hub router that is configured for ODR. Answer E is incorrect because the hub router does not need to be running any other routing protocol, although it often is. ODR information can be injected into other dynamic routing protocol information.

Question 7	Answer A is correct because by definition, classful routing protocols do not carry subnet mask information in routing updates. Answer B is correct because RIP v1 and IGRP are examples of early classful routing protocols. Answer C is incorrect because subnet mask information is not carried in routing updates within the same network; consistency of the mask is assumed. Network boundary summarization is performed automatically. Answer D is incorrect because if routing update information contains a different major network than the one configured on the receiving interface, the router applies the default classful mask by IP address class.

Question 8	Answer D is correct because the traffic is bound for an unknown subnet of the 10 network. Therefore, the traffic is discarded. This behavior is a result of the lack of the `ip classless` command. Answer A is incorrect because the 10.2.2.2 destination does not match the first entry, nor does it match the third entry, Answer B, in the routing table. Answer C is incorrect because the default route entry would be used to route the traffic only if the `ip classless` command is used.

Question 9	Answer B is correct because in RIP version 2 you turn off auto summarization by using the `no auto-summary` command under the RIP process. Answer D is also correct because you can use the `ip summary-address rip` interface command and define a network number and mask that meets the particular requirements. Answers A and C are incorrect because neither is capable of configuring manual summarization.

Question 10	Answer A is correct because the administrative distance value of 20 assigned to external BGP enables it to be preferred over most other dynamic protocols. These other values are assigned to the following protocols: Answer B is incorrect because internal EIGRP is 90; Answer C is incorrect because EIGRP summary route is 5; Answer D is incorrect because IGRP is 100; and Answer E is incorrect because OSPF is 110.

Question 11	Answers A, B, and E are correct because even though they are classless protocols, RIPv2, EIGRP, and BGP all exhibit automatic route summarization by default. Answers C and D are incorrect because IS-IS and OSPF do not automatically summarize IP address information. Summarization must be manually configured if it is to be used.

Question 12	Answer C is correct because the Level 1/2 router learns about paths both within and between areas. L1/2 routers are equivalent to ABRs in OSPF. Answer A is incorrect because L1 routers learn about paths within the areas to which they connect. Answer B is incorrect because L2 routers learn about paths among areas. Answer D is incorrect because L1/2 routers learn about paths within and between areas.

Question 13	Answer A is correct because even though IS-IS metrics can consist of default, delay, expense, and error components , Cisco supports only the default value. Answer C is also correct because if not manipulated, this default value has the IS-IS metric function very similar to RIP in that it is a simple measure of hop count. Answer B is incorrect because the Cisco router assigns a default metric value of 10 to each IS-IS interface. Answer D is incorrect because Narrow metrics are limited to a 6-bit interface and 10-bit path metric. Cisco has addressed this in post 12.0 IOS routers by using a wide metric value.

Question 14	Answer B is correct because Level 1 routing is also called area routing. It deals with IS moving data within an area. Answer A is incorrect because Level 0 routing deals with moving data from an end system to an IS. Answer C is incorrect because Level 2 routing is known as inter-area routing. Answer D is incorrect because Level 3 routing deals with moving data between domains.

Question 15	Answer A is correct because IS-IS is easy to extend through the Type, Length, and Value mechanism. Also, answer E is correct because based on the default timers, IS-IS detects a failure in the network faster than OSPF. Answer B is incorrect because OSPF does have the advantage of more engineers and documentation being available. Answer C is incorrect because the metric of OSPF automatically scales to represent bandwidth by default. The default metric for IS-IS used by Cisco does not. Also answer D is incorrect because OSPF has more customized features for IP because the protocol was designed to run IP.

Question 16	Answer B is correct because the NSEL identifies a process on the device. It is roughly the equivalent to a port or socket in IP. Answer A is incorrect because the area address is used to identify areas in the IS-IS routing domain. Answer C is incorrect because the system ID identifies an individual OSI device. Answer D is incorrect because the HODSP subdivides the domain into areas. It is roughly equivalent to a subnet in IP.

Question 17	Answer A is correct because each IS-IS router requires a unique system ID. Answer B is correct because on Cisco routers, this value must be 6 bytes. Typically, administrators use the MAC address of a LAN interface for this value. This ensures uniqueness throughout the domain. An IP address from an interface can also be used. Answer C is incorrect because System IDs are not 8 bytes, and answer D is incorrect because System IDs are used in IS-IS.

Question 18	Answer D is correct because for HDLC interfaces, the SNPA is simple HDLC. Answer A is incorrect because the MAC address is used as the SNPA for a LAN interface. Answer B is incorrect because the Virtual Circuit ID is used for X.25 or ATM interfaces. Finally, answer C is incorrect because the DLCI is used for Frame Relay interfaces.

Question 19	Answer C is correct because partial sequence number PDUs are used to acknowledge and request missing pieces of link-state information. Answer A is incorrect because IS-IS `Hellos` are used to maintain adjacencies between neighboring routers. Answer B is incorrect because link-state PDUs are used to distribute link-state information. Answer D is incorrect because complete sequence number PDUs are used to describe the complete list of LSPs in a router's link-state database.

Question 20	Answer A is correct because the `show clns route` command displays the IS-IS routing table. Answer B is incorrect because the `show ip route` command displays the IP IS-IS routes in the IP routing table. Answer C is incorrect because the `show isis database` command displays the contents of the IS-IS LSDB. Answer D is incorrect because the `show isis route` command displays the IS-IS L1 routing table, which includes all other system IDs in the area.

Question 21	Answer B is correct because when configuring Integrated IS-IS, you must configure the interfaces that are to participate by entering interface configuration mode and using the `ip router isis` command. Answer A is incorrect because the `network` command is not used with IS-IS. Answer C is incorrect because the NET configured on the router does not dictate what interfaces actually route traffic. Answer D is incorrect because there is no such thing as an `isis` interface map statement.

Question 22	Answer A is correct because during autoconfiguration, the router sends a network prefix to enable the autoconfiguration of the host. The prefix also contains a lifetime. Answers B, C, and D are incorrect because the information that the router sends includes one or more prefixes to use on the link, the lifetime information, flags, default router information, and other types of host information. Entire network addresses, MAC addresses, and host addresses are not sent.

Question 23	Answer C is correct because the Flow Label field tags flows of IP packets. It can be used for multilayer switching and faster packet switching. Answer A is incorrect because the Version field indicates the version of IP in use. Answer B is incorrect because the Traffic Class field is similar to the ToS field in IPv4. Answer D is incorrect because the Next Header value determines the type of information following the basic IPv6 header.

Question 24	Answer C is correct because the `show ip nat translations` command enables you to examine the IP NAT translation table. Answers A, B, and D are incorrect. All other commands listed here produce syntax errors.

Question 25	Answer B is correct because the inside global IP address is the IP address of an inside host as it appears to the outside network. Answer A is incorrect because the inside local IP address is the IP address of an internal host prior to any translation. Answer C is incorrect because the outside global IP address is the ISP-configured IP address configured on an external host. Answer D is incorrect because the outside local IP address is the external address of a host as it appears on the inside network.

Question 26	Answer A is correct because the best summary route is 172.24.4.0 with a 20-bit mask. This masks off all the bits that are identical in the 11 networks. Answers B, C, D, and E are incorrect. No other address in the options masks off all the bits that are identical in all the addresses.

Question 27	Answer D is correct because 16 additional subnetworks are gained when you use one of your subnets from the /20 mask scheme and use a mask of /24. This happens because 4 additional bits are "borrowed." Plugging these 4 bits into the formula 2^n yields 16 subnets. Answers A, B, C, and E are incorrect because no other number of subnets provided is the appropriate result of the formula.

Question 28	Answer D is correct because VLSM enables a very efficient use of IP address space. For point-to-point serial connections that require only two addresses, the 255.255.255.252 subnet mask meets the requirement ideally . Answers A, B, and C are incorrect because all other subnet masks presented result in address space waste. More host addresses are possible than can be used.

Question 29	Answer C is correct because IGRP is a "first-generation" routing protocol. It is classful in nature and as such does not support VLSM. Answers A, B, D, and E are incorrect. These are all classless and support VLSM.

Question 30	Answer A is correct because VLSM is supported in classless routing protocols and allows for efficient use of IP address space. Answer C is correct because VLSM designs also allow for more use of route summarization. Answer B is incorrect because subinterfaces allow the creation of additional logical interfaces in a single physical interface. Answer D is incorrect because not all routing protocols support VLSM ”classful routing protocols do not, for example.

Question 31	Answer B is correct because the term successor refers to the best next-hop router to reach a given network destination. Answers A, C, and D are incorrect. Feasible successor refers to an EIGRP backup route. Primary and designated are not terms that apply to EIGRP routes.

Question 32	Answer B is correct because the feasible distance is the distance from the local router to the destination. Answer A is incorrect because the advertised distance is the EIGRP metric for an EIGRP neighbor to reach a particular network. Answer C is incorrect because the feasible successor is the backup route to a destination. Answer D is incorrect because there is no such term as "successor distance."

Question 33	Answer B is correct because the mathematical formula to ensure that the feasible successor is loop-free requires that the AD of the second-best route be less than the FD of the successor. Answers A, C, and D are incorrect because they do not properly state the mathematical formula as it exists.

Question 34	Answers B, C, and D are correct. With K values at their defaults, the default metric for EIGRP consists of bandwidth and delay. EIGRP does not form a neighbor relationship with another router if that router uses different K values. IGRP-to-EIGRP conversions are simple: The metric of IGRP is multiplied by 256. Answer A is incorrect because the default K value settings are K1=1; K2=0; K3=1; K4=0; K5=0.

Question 35	Answers C, D, and E are correct because EIGRP reliable packets are packets that require explicit acknowledgement. These packets are Update, Query, and Reply packets. Answers A and B are incorrect. Hello and ACK packets are unreliable and do not require explicit acknowledgement .

Question 36	Answer B is correct because by default, EIGRP uses up to 50% of the bandwidth of an interface or subinterface. This bandwidth amount is set with the bandwidth interface parameter. Answers A, C, and D are incorrect. To change the bandwidth that EIGRP can use on a WAN interface, use the `ip bandwidth-percent eigrp` interface configuration command.

Question 37	Answer C is correct because OSPF does require additional router resources, including CUP and memory. Answer A is incorrect because OSPF tends to converge faster than most distance vector “based dynamic routing protocol approaches. Answer B is incorrect because there is no simple hop count limitation in the protocol. Answer D is incorrect because cost is the default metric. By default, cost calculations are based on bandwidth.

Question 38	Answer A is correct because two routers belonging to the same area have identical LSDBs for that area. Answer B is incorrect because each router may maintain a unique routing database with unique entries toward particular destinations. Answers C and D are incorrect because each maintains a neighborship and area database that also may be unique.

Question 39	Answer E is correct because after all LSRs have been satisfied for a given router, the adjacent routers are considered synchronized and in the full state. Answers A, B, C, and D are incorrect. The process of sending LSRs is called the loading state. After the DR and BDR have been selected, the routers are considered to be in the `exstart` state.

Question 40	Answer C is correct because the router with the highest priority wins the role of DR. Answers A, B, and D are incorrect. All other routers must have higher priority values to be considered the DR.

Question 41	Answer D is correct because the router ID is the highest loopback interface address configured on a router. Answers A, B, and C are incorrect. Loopback interfaces receive immediate priority over other interfaces for router ID selection.

Question 42	Answer C is correct because the point-to-multipoint mode treats the nonbroadcast network as a collection of point-to-point links. Answers A, B, and D are incorrect. These are not the correct operation mode.

Question 43	Answer F is correct because link-state update information is not found in a Hello packet. Answers A, B, C, D, and E are incorrect. The Hello packet contains routerID, hello and dead intervals, neighbors, area ID, router priority, DR and BDR IP addresses, authentication password, and stub area flag.

Question 44	Answer B is correct because setting the priority to a value of 0 ensures that the router never wins the DR election. Answer A is incorrect because setting the priority value to a high value ensures that the router wins the election process. Answer C is incorrect because creating a loopback interface on the router ensures the router ID value. Answer D is incorrect because there is no `election` command.

Question 45	Answer B is correct because the `neighbor` command is used to statically define adjacent relationships in NBMA networks. Answers A, C, and D are incorrect. A DR and BDR are elected. All serial ports are part of the same IP subnet. NBMA is an RFC-compliant mode.

Question 46	Answer D is correct because using the address and wildcard mask of 0.0.0.0 255.255.255.255 matches all interfaces on the router. Answers A, B, and C are incorrect. `All` and `any` are not valid keywords for use with the `network` statement.

Question 47	Answer D is correct because you can use the `show ip ospf interface` command with no arguments to display summarized OSPF information about all interfaces and composite links. Answers A, B, and C are incorrect. No other command provided gives information about OSPF priority values.

Question 48	Answer D is correct because using multiple areas enables routing tables to be reduced in size, thanks to summarization. Also, SPF calculations can be reduced because network details can be hidden from different areas. Answers A, B, and C are incorrect. SPF calculations do not tend to increase in size, nor do routing tables increase in size. Topology tables are not increased in size.

Question 49	Answer C is correct because hierarchical routing protocols are OPSF and IS-IS. They allow for the creations of areas to increase the scalability of the routing protocol. Answers A, B, and D are incorrect. Answer A is incorrect because distance vector approaches are first-generation technology. Answer B is incorrect because link-state routing protocols do not provide a hierarchical approach by default. Answer D is incorrect because there is no such category as "reliable protocols."

Question 50	Answer D is correct because an autonomous system boundary router makes a connection to another AS. Answers A, B, and C are incorrect. An ABR makes connections between two areas. An internal router exists in only one area. A backbone router makes a connection to Area 0.

Question 51	Answer E is correct because the external LSA type that describes routes to networks outside the OSPF AS is type 5. Answers A, B, C, and D are incorrect. No other LSA types describe these external networks.

Question 52	Answer G is correct. Types 3, 4, and 5 are blocked from a totally stubby area. Totally stubby areas do not accept information about routes external to the ASs or summary routes from other areas internal to the AS. Answers A, B, C, D, E, and F are incorrect. Totally stubby areas do not block Type 1 and 2 LSAs.

Question 53	Answer D is correct because IGRP and EIGRP are compatible. In fact, redistribution is automatic when the same AS number is used. Answer A is incorrect because redistribution should be used only when absolutely necessary. Answer B is incorrect because redistribution is possible between IGRP and EIGRP. Answer C is incorrect because hop count is not always the metric; the metric depends on the metric of the receiving protocol.

Question 54	Answer A is correct because you can use the `match length` command to specify the match criteria. You can specify one or both of the following: matches the Level 3 length of the packet and/or matches the source and destination IP address that is permitted by one or more standard or extended access lists. If you do not specify a `match` command, the route map applies to all packets. Answers B, C, and D are incorrect. All these command examples produce syntax errors.

Question 55	Answer C is correct because periodic updates are not used to ensure topological awareness. Triggered updates are used. Answers A, B, and D are incorrect. All these statements are indeed valid.

Question 56	Answer A is correct because these systems are typically directly connected. Answers B, C, and D are incorrect. All these statements regarding EBGB are false.

Question 57	Answer A is correct because the synchronization rule prevents "black holes" ”the route must be learned from an IGP first. Answers B, C, and D are incorrect because all these responses are invalid.

Question 58	Answer D is correct because you should use the `neighbor remote-as` command. This looks strange if the neighbor is in your AS, but the configuration is valid. Answers A, B, C and E are incorrect. The syntax is incorrect in all of these.

Question 59	Answer B is correct because after receiving an update from a client, the route reflector sends the update to all nonclient peers and all clients with the exception of the originator. Answers A, C, and D are incorrect. None of these statements accurately describe route reflector behavior.

Question 60	Answer B is correct because of the use of the `route-reflector-client` syntax with the `neighbor` command. This command is part of the `neighbor` statement. It tells the route reflector to start "reflecting" IBGP routes to and from the client. Answers A, C, and D are incorrect. None of these syntax examples are valid.