Cisco 642-902 Online Practice Questions and Exam Preparation

Cisco 642-902 Online Questions & Answers

• Question 21:

  Refer to the exhibit.

  

  Which two statements are true? (Choose two.)

  A. The eigrp stub command prevents queries from being sent from R2 to R1.
  B. The eigrp stub command will automatically enable summarization of routes on R2.
  C. The eigrp stub command prevents all routes except a default route from being advertised to R1.
  D. Router R1 will advertise connected and summary routes only.
  E. Router R1 will advertise connected and static routes. The sending of summary routes will not be permitted.
  F. Router R1 is configured as a receive-only neighbor and will not send any connected, static or summary routes.
  A. The eigrp stub command prevents queries from being sent from R2 to R1.
  D. Router R1 will advertise connected and summary routes only.

  ---

  The command "eigrp stub" turns R1 into a stub router so R2 will never send any query to R1 because R2 knows that a stub router will only route packets for networks it has explicitly advertised.

  The command "eigrp stub" is same as "eigrp stub connected summary" command because connected and summarized routes are advertised by default.

  Note: Because the network 192.168.50.0 is not advertised by "network" statement, it is necessary to redistribute connected route with the "redistribute connected" command.

• Question 22:

  Refer to the exhibit. Two routers are connected by Frame Relay and are running OSPF between them. Each router has been configured with the appropriate network statements under router ospf 1, but the routers are not forming an adjacency. Which of the following three commands could be configured on each router to correct this problem? (Choose three.)

  

  A. RouterC(config-if )#ip ospf network broadcast RouterD(config-if )#ip ospf network broadcast
  B. RouterC(config-if)#ip ospf network point-to-point RouterD(config-if)#ip ospf network point-to-point
  C. RouterC(config-router)#neighbor 10.100.100.4 RouterD(config-router)#neighbor 10.100.100.3
  D. RouterC(config-router)#neighbor 10.255.255.254 RouterD(config-router)#neighbor 10.255.255.253
  A. RouterC(config-if )#ip ospf network broadcast RouterD(config-if )#ip ospf network broadcast
  B. RouterC(config-if)#ip ospf network point-to-point RouterD(config-if)#ip ospf network point-to-point
  D. RouterC(config-router)#neighbor 10.255.255.254 RouterD(config-router)#neighbor 10.255.255.253

  ---

  By default, Frame Relay is classified as a non-broadcast network, meaning it doesn't send any broadcasts/multicasts like RIP, OSPF or EIGRP updates across the network (hello packets of OSPF are multicast to 224.0.0.5). Hence, in NBMA network, the neighbors are not discovered automatically; they must be configured manually. There are two ways to simulate a broadcast model on an NBMA network:

  + Define the network type as broadcast with the "ip ospf network broadcast" interface sub- command + Configure the neighbor statements under router ospf mode (though configuring the neighbor statement on one end is sufficient to form adjacency, it is a good practice to have it configured on both the ends)

  Besides these two ways, another way for making OSPF work with Frame Relay is configuring the network as a Point-to-Point network (or Point-to- Multipoint, notice that OSPF treats Point-to-Multipoint network as a collective of point-to-point links).

  Some information about Point-to-Multipoint (or Point-to-Point) network:

  Note: Point-to-Multipoint networks do not maintain a DR/BDR relationship.

• Question 23:

  Refer to the exhibit. OSPF is configured on all routers in the network. On the basis of the show ip ospf neighbor output, what prevents R1 from establishing a full adjacency with R2?

  

  A. Router R1 will only establish full adjacency with the DR and BDR on broadcast multiaccess networks.
  B. Router R2 has been elected as a DR for the broadcast multiaccess network in OSPF area
  C. Routers R1 and R2 are configured as stub routers for OSPF area 1 and OSPF area 2.
  D. Router R1 and R2 are configured for a virtual link between OSPF area 1 and OSPF area 2.
  E. The Hello parameters on routers R1 and R2 do not match.
  A. Router R1 will only establish full adjacency with the DR and BDR on broadcast multiaccess networks.

  ---

  From the output, we learn that R4 is the DR and R3 is the BDR so other routers will only establish full adjacency with these routers. All other routers have the two-way adjacency established.

• Question 24:

  Your network consists of a large hub-and-spoke Frame Relay network with a CIR of 56 kb/s for each spoke. Which statement about the selection of a dynamic protocol is true?

  A. EIGRP would be appropriate if LMI type ANSI is NOT used.
  B. EIGRP would be appropriate, because the Frame Relay spokes could be segmented into their own areas.
  C. EIGRP would be appropriate, because by default, queries are not propagated across the slow speed Frame Relay links.
  D. EIGRP would be appropriate, because you can manage how much bandwidth is consumed over the Frame Relay interface.
  D. EIGRP would be appropriate, because you can manage how much bandwidth is consumed over the Frame Relay interface.

  ---

  By default, EIGRP will limit itself to using no more than 50% of the interface bandwidth. The primary benefit of controlling EIGRP's bandwidth usage is to avoid losing EIGRP packets, which could occur when EIGRP generates data faster than the interface line can absorb it. This is of particular benefit on Frame Relay networks, where the access interface bandwidth and the PVC capacity may be very different.

  For example, in our Frame Relay topology a Hub is connected with 4 Spoke routers. The main Frame Relay interface on Hub router is 512Kpbs which is not enough to use for 6 links of 128 Kbps ( = 768 Kbps).

  

  The solution here is we can use 512 / 6 = 85 Kbps on each subinterface of Hub by using "bandwidth 85 command. For example:

  Hub(config)#interface Serial0/0.1 point-to-point

  Hub(config-subif)#bandwidth 85

  Also on Spoke routers we need to set this value. For example on Spoke1:

  Spoke1(config)#interface Serial0/1.0 point-to-point

  Spoke1(config-subif)#bandwidth 85

  Notice that by default, EIGRP limits itself to use no more than 50% of the configured interface bandwidth. In this case EIGRP will not use more than 42.5 Kbps (50% of 85 Kbps).

  (For more information about implementing EIGRP over Frame Relay, please read http://www.cisco.com/en/US/tech/tk365/ technologies_tech_note09186a0080094063.shtml)

• Question 25:

  Which two routing interface parameters are supported in OSPF implementations? (Choose two.)

  A. retransmit-interval
  B. dead-interval
  C. stub area
  D. virtual link
  E. NSSA area
  A. retransmit-interval
  B. dead-interval

  ---

  When OSPF sends an advertisement to an adjacent router, it expects to receive an acknowledgment from that neighbor. If no acknowledgment is received, the router will retransmit the advertisement to its neighbor. The retransmit-interval timer controls the number of seconds between retransmissions. To edit the retransmit-interval, use the "ip ospf retransmit-interval seconds" in interface configuration mode.

  Dead-interval is the number of seconds without hello packets before an adjacency is declared down. To edit the dead-interval, use the "ip ospf dead- interval seconds" in interface configuration mode.

  Other answers are not correct because they are not interface parameters.

• Question 26:

  What two situations could require the use of multiple routing protocols? (Choose two)

  A. when using UNIX host-based routers
  B. when smaller broadcast domains are desired
  C. because having multiple routing protocols confuses hackers
  D. when migrating from an older Interior Gateway Protocol (IGP) to a new IGP
  E. when all equipment is manufactured by Cisco
  F. when there are multiple paths to destination networks
  A. when using UNIX host-based routers
  D. when migrating from an older Interior Gateway Protocol (IGP) to a new IGP

  ---

  Simple routing protocols work well for simple networks, but networks grow and become more complex. While running a single routing protocol throughout your entire IP internetwork is desirable, multiprotocol routing is common for a number of reasons, including company mergers, multiple departments managed by multiple network administrators, multivendor environments, or simply because the original routing protocol is no longer the best choice. Often, the multiple protocols are redistributed into each other during a migration period from one protocol to the other.

• Question 27:

  What are two Cisco IOS commands that can be used to view neighbor adjacencies? (Choose two.)

  A. show ip ospf database
  B. show ip ospf neighbors
  C. show ip ospf protocols
  D. show ip ospf interfaces
  B. show ip ospf neighbors
  D. show ip ospf interfaces

  ---

  The output of these commands are shown below:

  

  

  Notice that for the "show ip ospf interface" command, the "Neighbor Count" is the number of OSPF neighbors discovered on this interface while the "Adjacent neighbor count" is the number of routers running OSPF that are fully adjacent with this router. Adjacent means that their databases are fully synchronized. In this example, this router has one neighbor on its Ethernet0 interface.

• Question 28:

  What does the default value of the EIGRP variance command of 1 mean?

  A. Load balancing is disabled on this router.
  B. The router performs equal-cost load balancing.
  C. Only the path that is the feasible successor should be used.
  D. The router only performs equal-cost load balancing on all paths that have a metric greater than 1.
  B. The router performs equal-cost load balancing.

  ---

  The point of the question is about the balance configuration of EIGRP. If variance is 1, it means that it support Equal cost path.

• Question 29:

  Refer to the exhibit. Autonomous systems 200 and 300 have EBGP sessions established with their directly connected routers in autonomous system 100. IGP has been configured on all routers in autonomous system 100 and they successfully exchange routing updates. Traffic originated in autonomous system 200 cannot reach the destination autonomous system 300. What configuration should be done on the routers in autonomous system 100 in order for the traffic coming from autonomous system 200 to be forwarded to autonomous system 300?

  

  A. IBGP session must be established between routers R1 and R3, and the synchronization must be turned on.
  B. IBGP session must be established between routers R1 and R3, and the synchronization must be turned off.
  C. IBGP session must be established between routers R1 R2 and R2 R3, and the synchronization must be turned on.
  D. IBGP session must be established between routers R1 R2 and R2 R3, and the synchronization must be turned off.
  E. IBGP speakers within autonomous 100 must be fully meshed, and the synchronization must be turned on.
  F. IBGP speakers within autonomous 100 must be fully meshed, and the synchronization must be turned off.
  F. IBGP speakers within autonomous 100 must be fully meshed, and the synchronization must be turned off.

  ---

  The synchronization rule states that if an AS provides transit service to another AS, BGP should not advertise a route until all of the routers within the AS have learned about the route via an IGP. To understand why this rule exists, let's take an example if this rule is not there.

  

  Suppose Rt-A wants RT-B to access its local LAN 1.1.1.0, so it advertises this network through R1. R1 and R3 are running IBGP so R1 sends this update to R3 through R2 (using the next-hop-self to use its own interface's IP address). In turn, R3 announces to RT-B that it can reach 1.1.1.0 via R3.

  Now Rt-B really wants to send traffic to 1.1.1.0 so it will send to R3. R3 does a look up and sees that the network can be reachable via R1. It then does a lookup for R1s IP address and sees that it is reachable via R2 -> so it forwards packets to R2. But R2, running IGP (like OSPF), does not find an entry for 1.1.1.0 so R2 drops all the packets for that network a black-hole is created!

  That is why the BGP synchronization rule is born. With this rule, when R3 receives an advertisement for 1.1.1.0 from R1, it adds that route to its BGP table and before sending advertisement to RT-B, it first checks its IGP routing table to see whether an entry exists for that route. In this example, R3s IGP routing table does not know how to reach 1.1.1.0 so R3 will not advertise this network to RT-B. This route is only advertised to RT-B when IGP makes an entry in the routing table for 1.1.1.0.

  Well, now you understand the importance of BGP Synchronization rule but now I wish to explain why this rule causes trouble in fully-meshed IBGP!

  

  Synchronization prevents fully-meshed IBGP from working properly. Because no IGP is running so R3 cannot advertise any route to RT-B even if no black-hole exists in this topology.

  Note: A "fully-meshed" can be a physical fully-meshed topology or a topology where all routers in the same AS established IBGP connections with each other (although they do not need to be directly connected). So in the topology above, the

  connection between R1 and R3 is represented by a dashed line, which means it can be physically connected or not (but an IBGP connection must be established on both routers).

  Therefore if all routers in AS 100 is fully-meshed, the synchronization rule must be turned off.

• Question 30:

  What administrative distance is given to EIGRP summary routes?

  B. 1
  C. 5
  D. 90
  E. 95
  F. 170
  C. 5

  ---

  Reference:

  http://www.cisco.com/en/US/docs/ios/iproute_eigrp/command/reference/ire_i1.html (See usage guidelines)