Cisco CCNP Enterprise 300-410 Questions & Answers

• Question 141:

  A neighboring EIGRP router fails. Its advertised distance (AD) to network 10.10.10.0 was 2 and the feasible distance (FD) was 3.

  Which route will be used to route packets destined for network 10.10.10.0 if the other routes have the following feasible and advertised distances respectively to the destination network?

  A. FD-6 AD-3

  B. FD-4 AD-1

  C. FD-5 AD-3

  D. FD-4 AD-3

  Correct Answer: B

  When EIGRP loses it best route, called the successor route, it will then use a feasible successor route, if available, to route the packets to that destination. To be considered a feasible successor, the advertised distance, which is the

  neighboring router's distance, needs to be less than the feasible distance, which is the local router's own metric.

  In this scenario, the feasible distance is 3. The only available feasible successors are the ones that have the advertised distance/feasible distance of 1/4 and 2/4.

  Objective:

  Layer 3 Technologies

  Sub-Objective:

  Configure and verify policy-based routing

  References:

  Cisco > Home > Support > Technology Support > IP Routing > Technology Information > Technology White Paper > Enhanced Interior Gateway Routing Protocol > Feasible Distance, Reported Distance, and Feasible Successor

• Question 142:

  You have two routers connected to each other that are both running the EIGRP protocol. The routers have built a neighbor relationship and are exchanging routing information. You execute the following command on the EIGRP process on Router 1:

  router1(config)# router eigrp 100 router1(config-router)# passive-interface

  What will be the effect of this command?

  A. Only routing advertisements from Router 1 to Router 2 will be prevented.

  B. Only router advertisements to and from Router 1 will be prevented.

  C. All hellos and routing updates will be prevented, and the neighbor relationship between Router 1 and Router 2 will be broken.

  D. Hellos will be prevented, but routing updates will continue to be sent out.

  Correct Answer: C

  The effect of the passive-interface command is dependent on the routing protocol. With RIP, the command prevents the sending of route updates, but does not prevent the reception of route updates. With EIGRP, the passive-interface

  command prevents both the sending and receiving of route updates, and also the sending of hellos. Without hello packets, the routers are unable to maintain the neighbor relationship, upon which all communications including route updates

  depend.

  If the intent was to preventing routing updates from Router 1 to Router 2 while still allowing updates from Router 2 to Router 1, the routing updates must be filtered out and denied on Router 1 with a distribute list, as shown in the following

  command set:

  router1(config)access-list 101 deny any

  router1(config)#router eigrp 100

  router1(config-router)distribute-list 101 out

  Objective:

  Layer 3 Technologies

  Sub-Objective:

  Troubleshoot passive interfaces

  References:

  Cisco IOS Master Command List, Release 12.4T > p through r > passive-interface Cisco > Home > Support > Technology Support > IP > IP Routing > Design > Design Technotes > Filtering Routing Updates on Distance Vector IP Routing

  Protocols

• Question 143:

  You are the network administrator for a corporate organization. You changed the BGP configuration, then executed the following command on the rtrA router:

  clear ip bgp 172.161.18.5 soft out

  What is the result of this command?

  A. The outbound session between rtrA and 172.161.18.5 is cleared and reset.

  B. The inbound session between rtrA and 172.161.18.5 is cleared and reset.

  C. The outbound session between rtrA and 172.161.18.5 is cleared.

  D. The inbound session between rtrA and 172.161.18.5 is cleared.

  Correct Answer: C

  The outbound TCP session between rtrA and 172.161.18.5 is cleared as a result of the given command. The given command is a variation of the clear ip bgp command.

  The clear ip bgp command allows you to clear and reset the sessions or routing updates in BGP routers so that changes in the BGP configuration can take effect. You can use this command to clear and reset the sessions for all neighbors, a

  specific neighbor, or a group of neighbors. Use an asterisk (*) or the group name instead of the IP address to apply the command on all the neighbors of a router or a particular peer group, respectively.

  For example, if you execute the clear ip bgp * command, all the sessions currently active are cleared and reset. If you use the clear ip bgp 172.161.18.5 command on rtrA, the current session between rtrA and its neighbor 172.161.18.5 is

  cleared and reset. Such a reset of sessions is known as hard reset. When hard resets are performed, the neighbor relationship is broken and must be reestablished.

  The soft keyword, which is optional, indicates a soft reset. This keyword allows you to clear the BGP table without resetting the session. If you do not use this keyword, the sessions are cleared and then reset with a hard reset.

  The out keyword specifies that the command should be applied to only outbound sessions. If you use the in keyword, the command is applied to only inbound sessions.

  The outbound TCP session between rtrA and 172.161.18.5 is not cleared and reset by the given command. If the clear ip bgp 172.161.18.5 out command was used, then the outbound session between rtrA and 172.161.18.5 would be both

  cleared and reset.

  The inbound TCP session between rtrA and 172.161.18.5 is not cleared and reset by the given command. If the clear ip bgp 172.161.18.5 in command were used, then the inbound TCP session between rtrA and 172.161.18.5 would be

  cleared and then reset.

  The inbound TCP session between rtrA and 172.161.18.5 is not cleared by the given command. If the in keyword were used instead of the out keyword in the given command, the outbound TCP session between the rtrA and 172.161.18.5

  would be cleared.

  Objective:

  Layer 3 Technologies

  Sub-Objective:

  Describe, configure, and verify BGP peer relationships and authentication

  References:

  Cisco IOS IP Routing: BGP Command Reference > clear ip bgp

• Question 144:

  You are configuring Open Shortest Path First (OSPF) protocol for IPv6 on Router5. The router has two interfaces, which have been configured as follows:

  S0/0 - 192.168.5.1/24 S0/1 - 10.0.0.6/8

  You would like OSPF to route for IPv6 only on the S0/0 network and not route for IPv6 on the S0/1 network. The process ID you have chosen to use is 25. You do not want to apply an IPv6 address yet.

  Which of the following command sets would enable OSPF for IPv6 as required?

  A. Router5(config)#ipv6 ospf 25 Router5(config)# network 192.168.5.0

  B. Router5(config)#ipv6 ospf 25 Router5(config)#router-id 192.168.5.1

  C. Router5(config)#ipv6 unicast-routing Router5(config)#ipv6 router ospf 25 Router5(config-rtr)#router-id 1.1.1.1 Router5(config)#interface S0/0 Router5(config-if)#ipv6 ospf 25 area 0

  D. Router5(config)#ipv6 unicast-routing Router5(config)#ipv6 ospf 25 Router5(config-rtr)#router-id 1.1.1.1

  Correct Answer: C

  The correct command sequence would be as follows:

  Router5(config)# ipv6 unicast-routing Router5(config)# ipv6 router ospf 25 Router5(config-rtr)# router-id 1.1.1.1 Router5(config)# interface S0/0

  Router5(config-if)# ipv6 ospf 25 area 0

  The first line enables IPv6 routing with the ipv6 unicast-routing command. The second line enables OSPF routing for IPv6 with the ipv6 router ospf command. The third assigns a necessary router ID (which was chosen at random) with the

  router-id command. The last two lines enable OSPF for area 0 on the proper interface.

  The following command set is incorrect because it does not enable OSPF routing for IPv6, assign a necessary router ID, or enable OSPF for area 0 on the proper interface:

  Router5(config)# ipv6 ospf 25

  Router5(config)# network 192.168.5.0

  This command set also displays incorrect use of the network command. The network command would be used with OSPF v2.

  The following command set fails to enable OSPF routing for IPv6, assign a necessary router ID, or enable OSPF for area 0 on the proper interface:

  Router5(config)# ipv6 ospf 25

  Router5(config)# router-id 192.168.5.1

  It also assigns the router ID under global configuration mode, rather than under router ospf 25 configuration mode as required.

  The following command set fails to enable OSPF for area 0 on the proper interface:

  Router5(config)# ipv6 unicast-routing

  Router5(config)# ipv6 ospf 25

  Router5(config-rtr)# router-id 1.1.1.1

  Objective:

  Layer 3 Technologies

  Sub-Objective:

  Configure and verify OSPF for IPv6

  References:

  Cisco > Implementing OSPF for IPv6 > How to Implement OSPF for IPv6 Cisco > Cisco IOS IPv6 Command Reference > ipv6 unicast-routing Cisco > Cisco IOS IPv6 Command Reference > ipv6 ospf area

• Question 145:

  Refer to the following exhibit, where three routers have EIGRP for IPv6 enabled on them:

  

  What is the next-hop address when rtrB advertises the 2001:5050:D402:B333::/64 IPv6 subnet to rtrC?

  A. FE80::3030:3030:3030/64

  B. FE80::3230:3030:3030/64

  C. FE80::3030:30FF:FE30:3030/64

  D. FE80::3230:30FF:FE30:3030/64

  Correct Answer: D

  The next-hop address when rtrB advertises the 2001:5050:D402:B333::/64 IPv6 subnet to rtrC is FE80::3230:30FF:FE30:3030/64. In routers with EIGRP for IPv6 enabled on them, the next-hop address is the IP address of the interface that advertises routes. The next-hop addresses should be link-local addresses. Link-local addresses are IPv6 unicast addresses that are automatically assigned to the router interfaces. These addresses have the FE80::/10 prefix and the EUI-64 standard interface address.

  EUI-64 is an IEEE standard that allows the determination of an IPv6 address from the MAC address of an interface. The 64 most significant bits should be specified in the ipv6 address command. The 64 least significant bits are determined by using the EUI-64 standard. The steps to determine the 64 least significant bits are as follows:

  1.

  Divide the 48-bit MAC address into two 24-bit parts.

  2.

  Embed FFFE (16 bits) between the two parts resulting in a 64-bit address.

  3.

  If required, toggle the seventh bit of the first octet in the address. In EUI-64 format, if the seventh bit is 0, then the address is local. If the seventh bit is 1, the address is global.

  In this case, when rtrB advertises any route to rtrC, it advertises the interface with the MAC address 3030.3030.3030 as the next-hop. When the given steps are performed on the MAC address, it result in the EUI-64 standard address

  3230.30FF.FE30:3030. This address is then appended to the FE80::/10 prefix. The resultant IPv6 link-local address of the interface is FE80::3230.30FF.FE30:3030/10.

  The remaining three options are incorrect as their interface address is not in the EUI-64 standard.

  Objective:

  Layer 3 Technologies

  Sub-Objective:

  Identify IPv6 addressing and subnetting

  References:

  Cisco IPv6 Configuration Guide, Release 15.2 > IPv6 Neighbor Redirect Message Cisco IPv6 Configuration Guide, Release 15.2 > IPv6 Unicast Routing > Aggregatable Global Address

• Question 146:

  An OSPF area contains the following networks:

  165.164.8.0 255.255.254.0

  165.164.10.0 255.255.254.0

  165.164.12.0 255.255.254.0

  165.164.14.0 255.255.254.0

  How can the route to these networks be summarized?

  A. 165.164.8.0 255.255.240.0

  B. 165.164.8.0 255.255.248.0

  C. 165.164.10.0 255.255.252.0

  D. 165.164.14.0 255.255.240.0

  Correct Answer: B

  Summarization is the process of advertising a network with a subnet mask such that it includes all of the subnets. For a simple example if you had two Class C networks, you could advertise them as a Class B network and it would encompass them both. Normally summarization should be implemented such that it summarizes ONLY the networks desired and no others (in the simple example it would possibly include other Class C networks). The process for arriving at the "best" summarization is a follows.

  First, write the last octet that all networks share in common (third octet in this case) in binary form for each network:

  165.164.8.0--00001000 165.164.10.0--00001010 165.164.12.0--00001100 165.164.14.0--00001110

  The addresses have the first five bits in common; therefore, they can be summarized with the third octet 00001000 and a subnet mask of 255.255.248.0.

  Another way of looking at it is that 165.164.8.0 255.255.248.0 covers the range of 165.164.8.0 through 165.164.15.255, the same range as all the component subnets.

  None of the following possible answers is a valid range, nor do most of them cover the correct range of addresses:

  165.164.8.0 255.255.240.0 is not a valid range. A 20-bit mask can only be on a subnet that is a multiple of 16, such as .16.0, .32.0, .48.0 etc. The subnet .8.0 is not a multiple of 16.

  165.164.10.0 255.255.252.0 is not valid. A 22-bit mask requires a multiple of 4 in the third octet, and 10 is not a multiple of four. Even if it were a valid range, it does not cover the entire range of addresses that need to be summarized.

  165.164.14.0 255.255.240.0 is not valid. The 20-bit mask is only usable on ranges that are multiples of 16 in the third octet, and 14 is not a multiple of 16. Even if the mask were valid, it could not cover the correct addresses.

  When addresses are summarized the cost of the summary address will the highest cost of the component subnets. For example, in the partial sample output of the show ip route command below, there are three routes. The output is from a router running OSPFv3, so the addresses are IPv6, but the concept is the same.

  OI 2001:0D B 8:0:0:7/64 [110/20]

  via FE 80::A8BB:CCFF:FE 00:6F00, FastEthernet0/0

  OI 2001:0D B 8:0:0:8/64 [110/100]

  via FE 80::A8BB:CCFF:FE 00:6F00, FastEthernet0/0

  OI 2001:0D B 8:0:0:9/64 [110/40]

  via FE 80::A8BB:CCFF:FE 00:6F00, FastEthernet0/0

  The routes have metrics (the second value in brackets, [administrative distance/cost]) of 20, 100, and 40. Therefore, the metric for the summarized route would be 100.

  Objective:

  Layer 3 Technologies

  Sub-Objective:

  Configure and verify manual and autosummarization with any routing protocol

  References:

  Cisco > Home > Support > Technology Support > IP Routing > Technology > Information Technology > White Papers > OSPF Design Guide

• Question 147:

  You have implemented OSPF for IPv6 for the following areas in OSPF AS 1:

  

  The cost from rtrB to the 2001:5050:D402:B333:1:FE30::/96 network is 80, while the cost from rtrB to the 2001:5050:D402:B333:2:FE59::/96 network is 130.

  Which of the following area range cost commands should be executed on rtrB?

  A. area 10 range 2001:5050:D402:B333::/64 cost 80

  B. area 10 range 2001:5050:D402:B333::/64 cost 130

  C. area 10 range 2001:5050:D402:B333::/64 cost 210

  D. area 10 range 2001:5050:D402:B333::/64 cost 0

  Correct Answer: B

  The area 10 range 2001:5050:D402:B333::/64 cost 130 command should be executed on rtrB. This command defines an area range for an area border router (ABR) that has OSPF for IPv6 enabled on it. This command provides a summary

  route of the routes in an OSPF area to be distributed to another area.

  The range keyword in the command provides the summary route. The cost keyword in the command specifies the cost of the summary route. The highest cost of the routes that are being summarized becomes the cost of the summary route.

  In this case, the cost from rtrB to the 2001:5050:D402:B333:1:FE30::/96 network is 80, and the cost from rtrB to the 2001:5050:D402:B333:2:FE59::/96 network is 130. The cost of the summary route is 130 as it is higher.

  All the other options are incorrect because they do not specify the correct cost of the summary route.

  Objective:

  Layer 3 Technologies

  Sub-Objective:

  Configure and verify OSPF for IPv6

  References:

  Cisco Learning Home > Groups > CCNP RandS Study Group > Discussions > What would be the Metric for a Summary Route in OSPFv3

  Cisco IOS IPv6 Configuration Guide, Release 12.4 > Implementing OSPF for IPv6 > How to Implement OSPF for IPv6

• Question 148:

  You are using an aggregate static route to null 0 to redistribute static routes into BGP.

  Which problem can result if the router loses access to one of these routes?

  A. Black hole

  B. Routing loop

  C. Split horizon

  D. Unstable BGP table

  Correct Answer: A

  If one of the aggregated routes is lost, the router will discard packets destined for that route. This condition is known as a black hole.

  For example, suppose you have a number of subnets of range 11.1.0.0/16, all of which have 24 bit masks, such as 11.1.2.0/24. You aggregate them all to 11.1.0.0/16 and advertise that aggregate. If this router were to lose connectivity to one

  of the subnets, for example 11.1.3.0/24, then any traffic routed through this router to that subnet would never reach it, even if there were another valid path.

  Split horizon is a loop avoidance mechanism that is by default always in effect, and is not affected by the loss of a subnet route that is part of an aggregate route.

  BGP tables are not made unstable by the loss of the loss of a subnet route that is part of an aggregate route.

  Routing loops would not occur simply from the loss of a subnet route that is part of an aggregate route.

  Objective:

  Layer 3 Technologies

  Sub-Objective:

  Configure and verify manual and autosummarization with any routing protocol

  References:

  Cisco > IP Routing: BGP Configuration Guide > BGP4 > Aggregating Route Prefixes Using BGP

• Question 149:

  You have configured BGP on both rtrA in AS 1 and rtrB in AS 2. There are two routes created using the network command between the two routers. One route traverses through AS 5 and AS 6 from rtrA to rtrB, while the other route traverses AS 7, AS 8, and AS 9 from rtrA to rtrB. Both routes use default values for the Weight and LOCAL_PREF attributes.

  Which of the following attributes determines the BEST route between rtrA and rtrB routers?

  A. Weight

  B. LOCAL_PREF

  C. Origin type

  D. AS_PATH

  Correct Answer: D

  The AS_PATH attribute is used to determine the best path between the two routes. To select the best path from rtrA to rtrB, BGP analyzes attributes that are set for the two available routes during the configuration of the network. The key BGP attributes and the order in which they are checked are as follows:

  1.

  Weight - highest weight is selected

  2.

  LOCAL_PREF - highest LOCAL_PREF is selected

  3.

  Locally originated routes - local routes are selected

  4.

  AS_PATH - shortest AS_PATH is selected

  5.

  Origin type - lowest origin type is selected

  6.

  Multi-exit Discriminator (MED) - lowest MED is selected

  The weight attribute is the first attribute to be checked while selecting the best BGP route. This attribute is relevant only to the local router on which it is set. The value of this attribute can be any number from 0 to 65535. The default values are 32768 for locally originated routes and 0 for other types of routes. Both routes in this case are originated locally and have the default weight values. Therefore, in this case, the weight attribute is not used to determine the best route.

  BGP then checks the value of the LOCAL_PREF attribute, which refers to local preference. Local preference is a value indicates the route that is preferred to exit the AS to reach a given network. Routes with higher local preference are selected by BGP. You can set the local preference for a route to any value; however, if you do not, the route uses the default value of 100. Because both routes have the default LOCAL_PREF value, this attribute is not used to determine the best route.

  Next BGP checks whether any of the routes are locally originated using the network, redistribute, or aggregate commands. As stated, both routes originated using the network command on the routers. Consequently, BGP analyzes the value

  of the AS_PATH attribute, which is a list of the AS numbers traversed by a particular route. The route with the shortest AS_PATH is selected as the best path. In this case, the route that consists of AS 5 and 6 is considered the best path

  because the AS_PATH value for this route is shorter than that for the route traversing AS 7, 8, and 9. The AS_PATH value for the route traversing AS 5 and 6 is [6 5 1], while the AS_PATH for the route traversing AS 7, 8, and 9 is [9 8 7 1].

  The other options are incorrect because the corresponding attributes are same for both the routes; hence, those attributes are not considered while BGP determines the best path.

  Objective:

  Layer 3 Technologies

  Sub-Objective:

  Explain BGP attributes and best-path selection

  References:

  Internetworking Technology Handbook > BGP > BGP attributes

• Question 150:

  Examine the exhibit.

  

  Router R2 has been configured with the following OSPF router command:

  area 1 range 130.31.96.0 255.255.224.0

  Which addresses listed will be summarized by R2 into area 0? (Choose all that apply.)

  A. 130.31.128.0/23

  B. 130.31.112.0/20

  C. 130.31.130.0/24

  D. 130.31.160.0/22

  E. 130.31.104.0/21

  Correct Answer: BE

  The command area 1 range130.31.96.0 255.255.224.0 is used to summarize the IP network addresses from 130.31.96.0/24 to 130.31.127.0/24 in area 1. Addresses 130.31.112.0/20 and 130.31.104.0/21 are both in that range of network addresses.

  To determine if an address is a part of a summary, put the summary address and summary mask in binary format. Do the same with the address and the summary mask you are examining, as shown below:

  130.31.96.0 10000010.00001111.01100000.00000000

  130.31.112.0 10000010.00001111.01110000.00000000

  255.255.224.0 11111111.11111111.11100000.00000000

  If the address you are testing and the summary address agree to the point where the mask stops, then the test address is part of the summary. In this case, they agree through the 27th bit, so this address is a part of the summary. The same

  is true for the 130.31.104.0 address.

  In OSPF, you can only configure summarization on the border routers. The summaries need to be of routes within a single area. You summarize the routes of an area so that routers in another area do not see the individual networks, just the

  summary. The correct command is:

  area area id range ip-address mask

  The area id parameter is the number of the area whose networks are being summarized. For example, in the network shown in the exhibit, to summarize the networks within area 1 to 130.31.96.0/19 you would configure router R2 with the

  command area 1 range 130.31.96.0 255.255.224.0. This would not affect the routing tables of the routers within area 1, but instead make the routing tables of areas 0 and 2 smaller. These other routers would only have the summary route

  listed instead of the individual networks. Router 3 would only see the summary route 130.31.96.0/19.

  Objective:

  Layer 3 Technologies

  Sub-Objective:

  Configure and verify manual and autosummarization with any routing protocol

  References:

  Cisco > Home > Support > Technology Support > IP Routing > Technology Information > Technology White Paper > OSPF Design Guide > OSPF and Route Summarization > Inter-Area Route Summarization Cisco IOS Master Command

  List, Release 12.4 > a through b > area range