Slide 1: 642-902 - Implementing Cisco IP Routing (ROUTE)
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Slide 2: QUESTION: 1 Five Pass routers are connected together as shown in the diagram below: Exhibit:
10.0.0.0/8
HUB SITE
Pass-Guaranteed.com
Pass1 Pass2 10.1.1.0/24 Pass3 Pass4 Pass5
SPOKE SITES
You work as a network engineer at Pass.com. You study the exhibit carefully. Pass1 and Pass2 are summarizing the 10.0.0.0/8 network and advertising it to all routers. Which two EIGRP configurations will prevent unnecessary EIGRP updates from being sent and possibly causing 10.0.0.0/8 from being SIA on router Pass1 or Pass2? (Select two) A. Configure Pass3, Pass4, and Pass5 as EIGRP stub routers. B. Configure an ACL on the interface of Pass1 and Pass2. C. Configure Pass1 and Pass2 as EIGRP stub routers. D. Configure summary routes on Pass1 and Pass2 E. Configure static routing on Pass3, Pass4, and Pass5 Answer: A, D Explanation: A dual-homed remote will have two or more distribution (hub) routers. However, the principles of stub routing are the same as they are with a hub and spoke topology.
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Slide 3: 10.3.1.0/24
Pass-Guaranteed.com
Pass1 Distribution Router 1 (hub) Remote router (spoke) Pass2 Distribution Router 2 (hub) 10.1.1.0/24 Corporate network 10.2.1.0/24
It is not desirable for traffic from distribution router 2 to travel through any remote router in order to reach network 10.3.1.0/24. If the links are sized to handle the load, it would be acceptable to use one of the backup routes. However, most networks of this type have remote routers located at remote offices with relatively slow links. This problem can be prevented if proper summarization is configured on the distribution router and remote router. It is typically undesirable for traffic from a distribution router to use a remote router as a transit path. A typical connection from a distribution router to a remote router would have much less bandwidth than a connection at the network core. Attempting to use a remote router with a limited bandwidth connection as a transit path would generally produce excessive congestion to the remote router. The EIGRP Stub Routing feature can prevent this problem by preventing the remote router from advertising core routes back to distribution routers. Routes learned by the remote router from distribution router 1 will not be advertised to distribution router 2. Since the remote router will not advertise core routes to distribution router 2, the distribution router will not use the remote router as a transit for traffic destined for the network core. Reference: http://www.cisco.com/en/US/products/sw/iosswrel/ps1829/products_feature_guide09186a008008702 6.html QUESTION: 2 Company has chosen to use EIGRP for their network routing protocol. Which three statements are true regarding EIGRP? (Select three) A. By default, EIGRP uses the Dijkstra algorithm to determine the best path to a destination network based on bandwidth and delay.
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Slide 4: B. To speed convergence, EIGRP attempts to maintain a successor and feasible successor path for each destination. C. EIGRP uses hellos to establish neighbor relationships. D. By default, EIGRP performs auto-summarization across classful network boundaries. E. EIGRP uses an area hierarchy to increase network scalability. Answer: B, C, D Explanation: The default behavior of EIGRP routers is to automatically summarize routes at the network boundary. EIGRP routers maintain information regarding the successors and the feasible successors to each network destination. This information is useful in the convergence time whenever any of the links fail. EIGRP neighbors periodically use hellos to establish the relationship. Should any of the neighbors fail, triggered updates are sent to update the network regarding the topology change.
Incorrect Answer: A: The Dijkstra algorithm is used by link state routing protocols. EIGRP is considered to be a hybrid routing protocol. E: EIGRP networks are inherently flat, as each router is perceived as a peer to every other EIGRP router. IS-IS and OSPF utilize hierarchical network topologies. QUESTION: 3 You have been tasked with setting up summarization in the Company EIGRP network.
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Slide 5: Which two statements are true about EIGRP manual summarization? (Select two) A. Manual summarization is configured on a per interface basis. B. When manual summarization is configured, auto-summarization is automatically disabled by default. C. The summary address is assigned an administrative distance of 10 by default. D. Manual summaries can be configured with the classful mask only. E. The summary address is entered into the routing table and is shown to be sourced from the Null0 interface. Answer: A, E Explanation: EIGRP automatically summarizes routes at the classful boundary, the boundary where the network address ends as defined by class-based addressing. In most cases, auto summarization is a good thing, keeping the routing tables as compact as possible In the presence of discontinuous sub networks, automatic summarization must be disabled for routing to work properly. To turn off auto- summarization, use the command: Router(config-router)#no autosummary EIGRP also enables following manual configuration of a prefix to use as a summary address. Manual summary routes are configured on a per-interface basis. The interface that will propagate the route summary must first be selected and then defined with the ip summary-address eigrp command, which has the following syntax: Router(config-if)#ip summary-address eigrp autonomous-system- number ip- address mask administrative-distance D 2.1.0.0/16 is a summary, 00:00:22, Null0 Notice that the summary route is sourced from Null0, and not an actual interface. QUESTION: 4 Router Company14 is configured as an EIGRP stub router. What are three key concepts that apply when configuring the EIGRP stub routing feature in a hub and spoke network? (Select three) A. Stub routers are not queried for routes. B. A hub router prevents routes from being advertised to the remote router. C. A stub router should have only EIGRP hub routers as neighbors. D. EIGRP stub routing should be used on hub routers only. E. Spoke routers connected to hub routers answer the route queries for the stub router. F. Only remote routers are configured as stubs. Answer: A, C, F
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Slide 6: Explanation: The Enhanced Interior Gateway Routing Protocol (EIGRP) Stub Routing feature improves network stability, reduces resource utilization, and simplifies stub router configuration. Stub routing is commonly used in a hub and spoke network topology. In a hub and spoke network, one or more end (stub) networks are connected to a remote router (the spoke) that is connected to one or more distribution routers (the hub). The remote router is adjacent only to one or more distribution routers. The only route for IP traffic to follow into the remote router is through a distribution router. This type of configuration is commonly used in WAN topologies where the distribution router is directly connected to a WAN. The distribution router can be connected to many more remote routers. Often, the distribution router will be connected to 100 or more remote routers. In a hub and spoke topology, the remote router must forward all nonlocal traffic to a distribution router, so it becomes unnecessary for the remote router to hold a complete routing table. Generally, the distribution router need not send anything more than a default route to the remote router. When using the EIGRP Stub Routing feature, you need to configure the distribution and remote routers to use EIGRP, and to configure only the remote router as a stub. Only specified routes are propagated from the remote(stub) router. The router responds to queries for summaries, connected routes, redistributed static routes, external routes, and internal routes with the message "inaccessible." A router that is configured as a stub will send a special peer information packet to all neighboring routers to report its status as a stub router. Reference: http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/120newft/120limit/120s / 120s15/eigrpstb.htm QUESTION: 5 Company uses EIGRP as their internal routing protocol. Which three statements are true about EIGRP operation? (Select three) A. The maximum metric for the specific routes is used as the metric for the summary route. B. When summarization is configured, the router will also create a route to null 0. C. The summary route remains in the route table, even if there are no more specific routes to the network. D. Automatic summarization across major network boundaries is enabled by default. E. Summarization is configured on a per-interface level. Answer: B, D, E Explanation: Using the ip summary-address eigrp summarization command will causes the creation of an EIGRP summary default route to the null 0 interface with an administrative distance of 5. Caution should be taken when using this as a default route. The low administrative distance of this default route can cause this route to displace default routes learned from other neighbors from the routing table. If the default route learned from the neighbors is displaced by the summary default route, or if the summary
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Slide 7: route is the only default route present, all traffic destined for the default route will not leave the router, instead, this traffic will be sent to the null 0interface where it is dropped. By default, Cisco routers will automatically summarize EIGRP routes across major network boundaries. With EIGRP, You can configure a summary aggregate address for a specified interface. If there are any more specific routes in the routing table, EIGRP will advertise the summary address out the interface with a metric equal to the minimum of all more specific routes. Incorrect Answer: A: The metric used in a summary route is the best metric from among the summarized routes, not the maximum (worst). C: When all of the specific routes used within a summary route are deleted from the routing table, the summaryroute will also be deleted. QUESTION: 6 The Company network administrator has issued the "EIGRP stub" command on router Company8. What is the purpose of the "EIGRP stub" configuration command? A. to reduce the convergence time by enabling the EIGRP stub router to propagate the EIGRP queries from the EIGRP hub router. B. to increase scalability by limiting the EIGRP query range. C. to reduce the size of the routing table by blocking the D EX (External EIGRP) routes into the EIGRP stub router. D. to reduce the convergence time by enabling the EIGRP stub router to also perform query requests to the EIGRP hub router. E. None of the other alternatives apply. Answer: B Explanation: The Enhanced Interior Gateway Routing Protocol (EIGRP) Stub Routing feature improves network stability, reduces resource utilization, and simplifies stub router configuration. Stub routing is commonly used in a hub and spoke network topology. In a hub and spoke network, one or more end (stub) networks are connected to a remote router (the spoke) that is connected to one or more distribution routers (the hub). The remote router is adjacent only to one or more distribution routers. The only route for IP traffic to follow into the remote router is through a distribution router. This type of configuration is commonly used in WAN topologies where the distribution router is directly connected to a WAN. The distribution router can be connected to many more remote routers. Often, the distribution router will be connected to 100 or more remote routers. In a hub and spoke topology, the remote router must forward all nonlocal traffic to a distribution router, so it becomes unnecessary for the remote router to hold a complete routing table. Generally, the distribution router need not send anything more than a default route to the remote router. When using the EIGRP Stub Routing feature, you need to configure the distribution and remote routers to use EIGRP, and to configure only the remote router as a stub. Only specified routes are propagated from the remote(stub) router. The router responds to queries for summaries, connected
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Slide 8: routes, redistributed static routes, external routes, and internal routes with the message "inaccessible." A router that is configured as a stub will send a special peer information packet to all neighboring routers to report its status as a stub router. Any neighbor that receives a packet informing it of the stub status will not query the stub router for any routes, and a router that has a stub peer will not query that peer. The stub router will depend on the distribution router to send the proper updates to all peers. Router (config-router)# eigrp stub [receive-only | connected | static | summary] :Configures a remote router as an EIGRP stub router. Reference: http://www.cisco.com/en/US/products/sw/iosswrel/ps1829/products_feature_guide09186a008008702 6.html QUESTION: 7 Router Company1 is configured as shown below: router eigrp 100 network 10.0.0.0 eigrp stub Based on the information shown above, which two types of routes will be advertised?(Select two) A. Receive-only B. Stub C. Static D. Summary E. Connected F. Dynamic Answer: D, E Explanation: The Enhanced Interior Gateway Routing Protocol (EIGRP) Stub Routing feature improves network stability, reduces resource utilization, and simplifies stub router configuration. Stub routing is commonly used in a hub and spoke network topology. In a hub and spoke network, one or more end (stub) networks are connected to a remote router (the spoke) that is connected to one or more distribution routers (the hub). The remote router is adjacent only to one or more distribution routers. The only route for IP traffic to follow into the remote router is through a distribution router. This type of configuration is commonly used in WAN topologies where the distribution router is directly connected to a WAN. The distribution router can be connected to many more remote routers. Often, the distribution router will be connected to 100 or more remote routers. In a hub and spoke topology, the remote router must forward all nonlocal traffic to a distribution router, so it becomes unnecessary for the remote router to hold a complete routing table. Generally, the distribution router need not send anything more than a default route to the remote router. When using the EIGRP Stub Routing feature, you need to configure the distribution and remote routers to use EIGRP, and to configure only the remote router as a stub. Only specified routes are propagated from the remote(stub) router. The router responds to queries for summaries, connected routes, redistributed static routes, external routes, and internal routes with the message "inaccessible." A router that is configured as a stub will send a special peer information packet to all neighboring routers to report its status as a stub router. Any neighbor that receives a packet informing it of the stub status will not query the stub router for any routes, and a router that has a stub peer will not query that peer. The stub router will depend on the distribution router to send the proper updates to all peers. Router (config-router)# eigrp stub [receive-only | connected | static | summary] :Configures a remote router asan EIGRP stub router.
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Slide 9: QUESTION: 8 The Company EIGRP network is displayed below:
Based on the network shown above, what optional EIGRP configuration statements will be required to achieve full connectivity within AS 100? A. Use the EIGRP "no auto-summary" command on Company1 and Company2. B. Use the "passive interface" on the Company1 and Company2 interface that connects to the10.1.1.0/24 and 10.1.2.0/24 subnet respectively. C. Use the EIGRP "no auto-summary" command on Company3 and Company4. D. Use the "passive interface" command between the Company3 and Company1 connection and between the Company3 and Company2 connection. E. Use the "variance" command on Company3. F. None of the other alternatives apply. Answer: A Explanation: EIGRP automatically summarizes routes at the classful boundary, the boundary where the network address ends as defined by class-based addressing. In most cases, auto summarization is a good thing, keeping the routing tables as compact as possible. In the presence of discontiguous subnetworks, automatic summarization must be disabled for routing to work properly. To turn off auto-summarization, use the following command: Router(config-router)#no auto-summary QUESTION: 9 Study the exhibit below carefully:
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Slide 10: Pass# show ip route ….. C 10.1.3.0/24 is directly connected, Serial2 D 10.1.2.0/24 (90/10537472) via 10.1.1.2, 00:23:24. Serial1 D 10.0.0.0/0 is a summary, 00:23:20, Null0 C 10.1.1.0/24 is directly connected, Serial1 S 192.168.20.0/24 is directly connected, Ethernet0 If the configuration shown below is added to Company1, which three route entries will EIGRP advertise to neighboring routers? (Select three) router eigrp 10 network 10.0.0.0 eigrp stub A. 192.168.20.0/24 B. 10.1.2.0/24 C. 10.1.1.0/24 D. 10.1.3.0/24 E. 10.0.0.0/8 Answer: C, D, E Explanation: The Enhanced Interior Gateway Routing Protocol (EIGRP) Stub Routing feature improves network stability, reduces resource utilization, and simplifies stub router configuration. Stub routing is commonly used in a hub and spoke network topology. In a hub and spoke network, one or more end (stub) networks are connected to a remote router (the spoke) that is connected to one or more distribution routers (the hub). The remote router is adjacent only to one or more distribution routers. The only route for IP traffic to follow into the remote router is through a distribution router. This type of configuration is commonly used in WAN topologies where the distribution router is directly connected to a WAN. The distribution router can be connected to many more remote routers. Often, the distribution router will be connected to 100 or more remote routers. In a hub and spoke topology, the remote router must forward all nonlocal traffic to a distribution router, so it becomes unnecessary for the remote router to hold a complete routing table. Generally, the distribution router need not send anything more than a default route to the remote router. When using the EIGRP Stub Routing feature, you need to configure the distribution and remote routers to use EIGRP, and to configure only the remote router as a stub. Only specified routes are propagated from the remote(stub) router. The router responds to queries for summaries, connected routes, redistributed static routes, external routes, and internal routes with the message "inaccessible." A router that is configured as a stub will send a special peer information packet to all neighboring routers to report its status as a stub router. Any neighbor that receives a packet informing it of the stub status will not query the stub router for any routes, and a router that has a stub peer will not query that peer. The stub router will depend on the distribution router to send the proper updates to all peers. QUESTION: 10 The Company OSPF network has been segmented into numerous different areas. Which three choices below are advantages to creating multiple areas in OSPF? (Select three) A. Fewer hello packets B. Fewer adjacencies needed C. Less frequent SPF calculations D. Smaller routing tables
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Slide 11: E. Reduced Link State Update (LSU) overhead Answer: C, D, E Explanation: Three issues can overwhelm an OSPF router in a heavily populated OSPF network: high demand for router processing and memory resources large routing tables large topology tables. In a very large internetwork, changes are inevitable. OSPF routers are likely to run SPF calculations frequently, which deprive the router of precious CPU cycles and memory resources. Not only is the routing table frequently recalculated in a large OSPF network, but it also risks being over stuffed with multiple paths and hundreds of routes. Full routing tables make routers less efficient. Finally, the link-state database, which must contain a complete topology of the network, will also threaten to consume resources and slow down the router. Reduced frequency of SPF calculations - Because detailed route information is kept within each area, it is not necessary to flood all link-state changes to all other areas. Therefore, only those routers affected by a change need to run the SPF calculation. Smaller routing tables - When using multiple areas, detailed route entries for specific networks within an area are kept inside the area. Rather than advertise these explicit routes outside the area, the routes can be summarized into one or more summary routes. Advertising these summaries reduces the amount of LSAs propagated between areas but allows all networks to remain reachable. Reduced link-state update (LSU) overhead - LSUs can contain a variety of LSA types, including link- state information and summary information. Rather than send an LSU about each network to every area, advertise a single route or a few summarized routes between areas to reduce the overhead associated with LSUs that cross multiple areas. QUESTION: 11 Which of the three areas below are valid OSPF area types? (Select three) A. Stub B. Active C. Remote D. Backbone E. Ordinary or standard Answer: A, D, E Explanation: OSPF Area Types: The characteristics that are assigned to an area control the type of route information that it can receive. For example, the size of routing tables may need to be minimized in an OSPF area. In this case configure the routers to operate in an area that does not accept external routing information, Type 5 LSAs. The following are several area types that are possible: Standard area - A standard area can accept link updates and route summaries. Backbone area (transit area) When interconnecting multiple areas, the backbone area is the central entity to which all other areas connect. The backbone area is always Area 0. All other areas must connect to this area to exchange route information. The OSPF backbone has all the properties of a standard OSPF area. Stub area - A stub area is an area that does not accept information about routes external to the autonomous system, the OSPF internetwork, such as routes from non-OSPF sources. If routers need to reach networks outside the autonomous system, they use a default route. A default route is noted as0.0.0.0/0. Totally stubby area - A totally stubby area is an area that does not accept external autonomous system(AS) routes and summary routes from other areas internal to the autonomous system. Instead, if the router needs to send a packet to a network external to the area, it sends it
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Slide 12: using a 0.0.0.0/0 default route. Totally stubby areas are a Cisco proprietary feature. Not-so-stubby area (NSSA) - An NSSA is an area that is similar to a stub area but allows for importing external routes as Type 7 LSAs and translation of specific Type 7 LSA routes into Type 5 LSAs. QUESTION: 12 The Pass multi-protocol WAN is shown below:
In this network, routers Pass2, Pass3, Pass4, and Pass5 have OSPF enabled. What should be configured on the routers in area 1 to ensure that all default summary routes and redistributed EIGRP routes will be forwarded from Pass6 to area 1, and only a default route for all other OSPF routes will be forwarded from Pass5 to area 1. A. Pass5(config-router)# area 1 nssa no-summary Pass6(config-router)# area 1 nssa B. Pass5(config-router)# area 1 stub no-summary Pass6(config-router)# area 1 stub C. Pass5(config-router)# area 1 nssa Pass6(config-router)# area 1 nssa D. Pass5(config-router)# area 1 stub Pass6(config-router)# area 1 stub Answer: A Explanation: Not-so-stubby area (NSSA) - An NSSA is an area that is similar to a stub area but allows for importing external routes as Type 7 LSAs and translation of specific Type 7 LSA routes into Type 5 LSAs. To configure an OSPF area as a NSSA, configure all OSPF router interfaces that belong to the area using the following command syntax: Router(config- router)#area area-id nssa [no- summary] Typically, use the optional keyword no-summary when configuring NSSA on an ABR. This prevents Type 3and Type 4 summary routes from flooding the NSSA area and minimizes the routing tables within the area. In effect, the no-summary keyword makes the NSSA totally stubby. QUESTION: 13 The following output was seen on router Pass1:
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Slide 13: Pass1#show ip route ospf O A 6.0.0.0/0 (110/65) via 5.0.0.2, 00:00:18, Serial2/1/0 O N2 0.0.0.0/0 (110/1) via 5.0.0.2, 00:00:18, Serial2/1/0 Based on the output shown above, which of the following statements is true? A. A default route is configured on the local router. B. OSPF router 5.0.0.2 is an ABR. C. The default route is learned from an OSPF neighbor. D. Network 6.0.0.0/8 was learned from an OSPF neighbor within the area. E. None of the other alternatives apply. Answer: B Explanation: In this example, the network 6.0.0.0/8 shows that it was leaned via IA, or Inter-area. Since this came from a neighbor in a different area, then the neighbor router at 5.0.0.2 must be an ABR. The various route types used by OSPF are:
QUESTION: 14 Routers Pass1, Pass2, and Pass3 are part of OSPF area 100 as shown below:
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Slide 14: OSPF 100
1
Pass-Guaranteed.com
Pass1 Pass2 Pass3
2
3
DR
BRD
In the Pass network shown above, router Pass1 was elected the DR and Pass2 was elected the BDR. Assume that Pass1 fails, and that Pass2 takes the place of the DR while Pass3 becomes the new BDR. What will happen when Pass1 comes back online? A. Pass1 will take the place of DR immediately upon establishing its adjacencies. B. Pass1 will take the place of DR only if Pass2 fails. C. Pass1 will take the place of DR only if both Pass2 and Pass3 fail. D. A new election will take place establishing an all new DR and BDR based on configured priority levels an MAC addresses. Answer: C Explanation: If a router with a higher priority value gets added to the network, it does not preempt the DR and BDR. The only time a DR and BDR changes is if one of them is out of service. If the DR is out of service, the BDR becomes the DR, and a new BDR is selected. If the BDR is out of service, a new BDR is elected. In a multi access network, the router that is powered on first will generally become the DR, since the DR/BDR process is not pre-emptive. Reference:: CCNP Self-Study Second Edition P.243 Explanation: BGP uses TCP port 179 to establish and maintain neighbor relationships, so any access lists or firewalls must permit this port for BGP to function. By default, EBGP multi-hop is not enabled, so the EBGP peer must be directly connected in order for the local BGP router to know how to reach the EBGP peer.BGP uses neighbor statements that specify the AS number of the BGP peer. If it is the same number as the local BGP router process, then the BGP router knows that IBGP is used. If the AS number for the specified peer is different, then EBGP is used. Either way, the specified neighbor must be configured correctly, or the BGP peers will not become neighbors. QUESTION: 15
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Slide 15: Every routing protocol has a loop prevention mechanism. Which BGP attribute is used by BGP routers to prevent routing loops? A. Origin B. Weight C. AS-path D. Next-hop E. Local preference F. MED G. None of the other alternatives apply Answer: C Explanation: An AS_Path attribute is a well-known mandatory attribute, type code 2. It is the sequence of AS numbers that a route has traversed to reach a destination. The AS that originates the route adds its own AS number when sending the route to its external BGP peers. Thereafter, each AS that receives the route and passes it on to other BGP peers will prepend its own AS number to the list. Prepending is the act of adding the AS number to the beginning of the list. The final list has all the AS numbers that a route has traversed with the AS number of the AS that originated the route at the end of the list. This type of AS_Path list is called an AS_Sequence because all the AS numbers are ordered sequentially.BGP uses the AS_Path attribute as part of the routing updates, update packet, to ensure a loop free topology onthe Internet. Each route that gets passed between BGP peers will carry a list of all AS numbers that the route has already been through. If the route is advertised to the AS that originated it, that AS will see itself as part of the AS_Path attribute list and will not accept the route. BGP speakers prepend their AS numbers when advertising routing updates to other autonomous systems, external peers. When the route is passed to a BGP speaker within the same AS, the AS_Path information is left intact. QUESTION: 16 Which three conditions can cause BGP neighbor establishment to fail? (Select three) A. There is an access list blocking all TCP traffic between the two BGP neighbors. B. The EBGP neighbor is not directly connected, and the ebgp-multi-hop option is set to the default value. C. The IBGP neighbor is not directly connected. D. BGP synchronization is enabled in a Transit AS with fully-meshed IBGP neighbors. E. The BGP update interval is different between the two BGP neighbors. F. The BGP neighbor is referencing an incorrect AS number in its neighbor statement. Answer: A, B, F QUESTION: 17
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Slide 16: The Pass BGP network is shown below:
By default, when Pass2 passes BGP advertisements from Pass1 about network 192.168.2.0 to Pass3, what address will be listed as the next-hop address? A. 10.1.1.2 B. 10.1.1.1 C. 192.168.1.49 D. 192.168.1.50 E. None of the other alternatives apply Answer: D Explanation: The next hop attribute is a well-known mandatory attribute, type code 3. In terms of an IGP, such as RIP, the "next hop" to reach a route is the IP address of the router that has announced the route. The next hop concept with BGP is more complex and takes one of the following three forms: For EBGP sessions, the next hop is the IP address of the neighbor that announced the route. For IBGP sessions, where routes originated inside the AS, the next hop is the IP address of the neighbor that announced the route. For routes injected into the AS by way of EBGP, the next hop learned from EBGP is carried unaltered into IBGP. he next hop is the IP address of the EBGP neighbor from which the route was learned. When the route is advertised on a multi access medium, such as Ethernet or Frame Relay, the next hop is usually the IP address of the interface of the router. This will be the interface connected to the media that originated the route.
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Slide 17: 150.10.0.0
RTA
IBGP
150.10.30.1
RTB
150.10.50.1
170.10.20.1
AS100
Pass-Guaranteed.com
170.10.20.2
RTC
170.10.20.3
RTD
AS300
180.20.0.0
This example shows how the next hop behaves on a multiaccess network such as Ethernet. Assume that RTC and RTD in AS300 run OSPF . RTC runs BGP with RTA. RTC can reach network 180.20.0.0via 170.10.20.3. When RTC sends a BGP update to RTA with regard to 180.20.0.0, RTC uses as next hop170.10.20.3. RTC does not use its own IP address, 170.10.20.2. RTC uses this address because the network between RTA, RTC, and RTD is a multiaccess network. The RTA use of RTD as a next hop to reach 180.20.0.0is more sensible than the extra hop via RTC. Note: RTC advertises 180.20.0.0 to RTA with a next hop 170.10.20.3. Reference: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800c95bb.shtml Cisco Press BSCI Quick Reference Sheets, page 51. QUESTION: 18 A problem was reported that the 10.10.10.0/24 prefix was not injected into the local BGP table on a Company router named Company1. The following information is available from this router: Company1 Configuration: router bgp 65001 network 10.0.0.0 neighbor 172.16.1.1 remote-as 65002 no autoFor The Latest 642-902 Practice Exam Questions: Visit: 642-902
Slide 18: summary Routing table information: show ip route | include 10 O 10.10.10.0/24 [110/11] via 192.168.1.1, 2d00h, Ethernet0/0 Why is this prefix not in the local BGP table of the Company1? A. The 172.16.1.1 neighbor is down. B. The prefix 10.10.10.0/24 is not a 'connected' route. C. This route is not a BGP learned route. D. The network command is wrong. E. None of the other alternatives apply Answer: D Explanation: The network command is used with IGPs, such as RIP, to determine the interfaces on which to send and receive updates. The command also indicates which directly connected networks to advertise. However, when configuring BGP, the network command does not affect what interfaces BGP runs on. Therefore, configuring just a network statement will not establish a BGP neighbor relationship. This is a major difference between BGP and IGPs. The network statement follows this syntax: Router(configrouter)#network network- number [mask network-mask]In BGP, the network command tells the BGP process what locally learned networks to advertise. The network scan be connected routes, static routes, or routes learned by way of a dynamic routing protocol, such as RIP. These networks must also exist in the routing table of the local router or they will not be sent out in updates. The mask keyword can be used with the network command to specify individual subnets. Routes learned by the BGP process are propagated by default but are often filtered by a routing policy. In this example, the correct syntax should be "network 10.10.10.0 mask 255.255.255.0" under the BGP routing process. Without the correct subnet mask specified, the route will not get injected into the BGP routing table, even if it is learned via an IGP. In this case, the route is known via OSPF. QUESTION: 19 Observe the diagram shown below:
10.10.10.0/24
Pass3
Hub
Spoke
EBGP
Pass1
Pass-Guaranteed.com
Spoke
Pass2 11.11.11.0/24
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Slide 19: In this network, Company3 is the hub router and Company1 and Company2 are the spokes. There are no virtual circuits between the spoke locations. What is needed to successfully route traffic to the 11.11.11.0/24 network from Company1? A. The neighbor 10.10.10.1 next-hop-self command on Company2. B. The neighbor 10.10.10.1 next-hop-self command on Company1. C. The neighbor 10.10.10.1 next-hop-self command on Company3. D. Nothing is required. This is the default behavior on this topology. E. None of the other alternatives apply. Answer: C Explanation: Refer to the following example: BGP Next Hop (NBMA)
The common medium appears as a cloud in the diagram. If the common medium is a frame relay or any NBMA cloud, the exact behavior is as if you have connection via Ethernet. RTC advertises 180.20.0.0 to RTA with a next hop of 170.10.20.3.The problem is that RTA does not have a direct permanent virtual circuit (PVC) to RTD and cannot reach the next hop. In this case, routing fails. The next-hop-self command remedies this situation.next-hop-self Command For situations with the next hop, as in the BGP Next Hop (NBMA) example, you can use the next-hop-self command. The syntax is: neighbor {ip- address | peer-group-name} next-hop-self. The next-hop-self command allows you to force BGP to use a specific IP address as the next hop. For the BGP Next Hop (NBMA) example, this configuration solves the problem: RTC# router bgp 300neighbor 170.10.20.1 remote-as 100neighbor 170.10.20.1 next-hop-self RTC advertises 180.20.0.0 with a next hop equal to 170.10.20.2. Reference: http://www.cisco.com/warp/public/459/bgp-toc.html#bgpnexthop
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Slide 20: QUESTION: 20 A Company BGP router is configured as shown below: router bgp 65111 neighbor 172.16.1.1 remoteas 65111 neighbor 172.16.2.1 remote-as 65112 network 192.168.0.0 network 10.0.0.0 ! ip route 192.168.0.0 255.255.0.0 null0 The 192.168.0.0 network is not being propagated throughout the network. Based on the information shown above what is the reason the 192.168.0.0 route is not being advertised? A. The network 10.0.0.0 statement is missing mask 0.255.255.255. B. The network 192.168.0.0 statement is missing mask 0.0.255.255. C. The network 10.0.0.0 statement is missing mask 255.0.0.0. D. The network 192.168.0.0 statement is missing mask 255.255.0.0 E. The auto-summary configuration is missing. Answer: D Explanation: The network command is used with IGPs, such as RIP, to determine the interfaces on which to send and receive updates. The command also indicates which directly connected networks to advertise. However, when configuring BGP, the network command does not affect what interfaces BGP runs on. Therefore, configuring just a network statement will not establish a BGP neighbor relationship. This is a major difference between BGP and IGPs. The network statement follows this syntax: Router (config-router)#network network- number [mask network-mask]In BGP, the network command tells the BGP process what locally learned networks to advertise. The networks can be connected routes, static routes, or routes learned by way of a dynamic routing protocol, such as RIP. These networks must also exist in the routing table of the local router or they will not be sent out in updates. The mask keyword can be used with the network command to specify individual subnets. Routes learned by the BGP process are propagated by default but are often filtered by a routing policy QUESTION: 21 The Company BGP router is configured as shown below: router bgp 64000 neighbor 172.16.1.1 remote-as 64000 neighbor 10.1.1.2 remote-as 64550 network 200.52.1.192 mask 255.255.255.224 no synchronization aggregate-address 200.52.1.0 255.255.255.0 The BGP peers 172.16.1.1 and 10.1.1.2 in the above configuration are established and working, as well as the interface with IP address 200.52.1.192. Based on this information, which statement below is true about your configuration? A. Router Pass has an IBGP connection with neighbor 10.1.1.2. B. Router Pass has an EBGP connection with the neighbor 172.16.1.1.
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Slide 21: C. Router Pass advertises only a route 200.52.1.0 255.255.255.0 in BGP. D. Router Pass advertises only a route 200.52.1.192 255.255.255.224 in BGP. E. Router Pass advertises both the routes to 200.52.1.0 255.255.255.0 and 200.52.1.192 255.255.255.224 in BGP. F. None of the other alternatives apply Answer: E Explanation: The aggregate route, 200.52.1.0 255.255.255.0, and the more specific route, 200.52.1.192 255.255.255.224, will both be advertised. To only advertise the aggregate route the summary-only option of the aggregate-address command must be used. Note: The aggregate-address command is used to create an aggregate, or summary, entry in the BGP table. Incorrect Answer: A: The neighbor 10.1.1.2 belongs to another autonomous system and is a EBGP neighbor, not an IBGP neighbor. B: Router A and neighbor 172.16.1.1 belong to the same autonomous system and is an IBGP neighbor, not an EBGP neighbor. C: The summary-only option of the aggregate-address command is used to only advertise the summary and not the specific routes. D: The aggregate route, 200.52.1.0 255.255.255.0, will be advertised as well. QUESTION: 22 Based on the "show ip bgp summary" output shown below on router Company1, which two statements are true? (Select two)
A. The BGP session to the 10.2.2.2 neighbor is established. B. The router is attempting to establish a BGP peering session with the 10.1.1.1 neighbor.
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Slide 22: C. The router is attempting to establish a BGP peering session with the 10.2.2.2 neighbor. D. The BGP session to the 10.3.3.3 neighbor is established. E. The BGP session to the 10.1.1.1 neighbor is established. F. The BGP session to the 10.3.3.3 neighbor is established, but the router has not received any BGP routing updates from the 10.3.3.3 neighbor. Answer: C, E Explanation: Show ip bgp summary command displays the summary of all BGP connections. The six states of the BGP FSM are described as follows: Idle - Idle is the first state of a BGP connection. BGP is waiting for a start event. It is normally initiated by an administrator or a network event. At the start event, BGP initializes its resources and resets a connect retry timer. Then it starts listening for a TCP notice that BGP can transition back to Idle from any other state in case of errors. Connect - In the Connect state, BGP is waiting for the TCP connection to be completed. If the TCP connection is successful, the state transitions to Open Sent. If the TCP connection fails, the state transitions to the Active state, and the router tries to connect again. If the connect retry timer expires, the state remains in the Connect state, the timer is reset, and a TCP connection is initiated. In case of any other event, initiated by the system or the administrator, the state returns to Idle. Active - In the Active state, BGP is trying to acquire a peer by initiating a TCP connection. If it is successful, it transitions to OpenSent. If the connect retry timer expires, BGP restarts the connect timer and returns to the Connect state. While active, BGP is still listening for a connection that may be initiated from another peer. The state may go back to Idle in case of other events, such as a stop event initiated by the system or the operator. In general, a neighbor state that is switching between "Connect" and "Active" is an indication that something is wrong and that there are problems with the TCP connection. It could be because of many TCP retransmissions, or the incapability of a neighbor to reach the IP address of its peer. OpenSent - In the OpenSent state, BGP is waiting for an open message from its peer. The open message is checked for correctness. In case of errors, such as an incompatible version number or an unacceptable AS,the system sends an error notification message and goes back to idle. If there are no errors, BGP starts sending keepalive messages and resets the keepalive timer. At this stage, the hold time is negotiated and the smaller value is taken. If the negotiated hold time is zero (0), the hold timer and the keepalive timer are not restarted.At the OpenSent state, BGP recognizes whether the peer belongs to the same AS or to a different AS. BGP does this by comparing its AS number to the AS number of its peer. A same AS is an IBGP peer and a different AS is an EBGP peer. When a TCP disconnect is detected, the state falls back to Active. For any other errors, such as an expiration of the hold timer, BGP sends a notification message with the corresponding error code. Then it returns to the Idle state. OpenConfirm - While in OpenConfirm state, BGP is waiting for a keepalive or notification message. If a keepalive message is received, the state goes to the Established state, and the neighbor negotiation is complete. If the system receives an update or keepalive message, it restarts the hold time, assuming that the negotiated hold time is not zero. If a notification message is received, the state falls back to Idle. The system sends periodic keepalive messages at the rate set by the keepalive timer. In the case of any TCP disconnector in response to any stop event, initiated by the system or the administrator, the state returns to Idle.
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Slide 23: In response to any other event, the system sends a notification message with an FSM error code and returns to the Idle state. Established - Established is the final state in the neighbor negotiation. BGP starts exchanging update packets with its peers. If it is non-zero, the hold timer is restarted at the receipt of an update or keep alive message. QUESTION: 23 Network Topology Exhibit:
Pass-Guaranteed.com
.2 10.10.23.0/24 .3
AS 65100
AS 65200
Pass1
Pass2 Exhibit:
Pass2
S0/0
S0/1
Pass3
Pass3 Exhibit:
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Slide 24: You work as a network engineer at Pass.com. Study the exhibits carefully. BGP has been configured on the Pass routers in the network. However, the IBGP peers in autonomous system 65200 have not converged. In addition, this console message was generated on router Pass2:*Mar 1 03:09:07.729: %TCP-6-BADAUTH No MD5 digest from 10.10.23.2(179) to 10.10.23.3(11002) On the basis of the information that is provided, what is the cause of the problem? A. OSPF must be configured with the same MD5 authentication. B. BGP authentication can be used on iBGP peers when the connection is configured between the loopback interfaces. C. BGP authentication can be used on eBGP peers only. D. The password that is used for BGP authentication on both BGP peers in autonomous system 65200 must be the same. E. None of the other alternatives apply Answer: D Explanation: The above log message is relating the invalid MD5 password on neighbor. Both peers need to use the same password for MD5 authentication. QUESTION: 24
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Slide 25: The command "ipv6 ospf 1 area 0" was issued on router Company1. What is true about this command? A. It must be issued before the network command to enable the OSPF process for IPv6. B. It must be issued after the network command to enable the OSPF process for IPv6. C. It must be issued in router global configuration mode to enable the OSPF process for IPv6. D. It must be issued in interface configuration mode to enable the OSPF process for IPv6. E. None of the other alternatives apply Answer: D Explanation: Cisco IOS enables OSPFv3 using interface subcommands, instead of using the OSPFv2 method (using the network command in router configuration mode). To enable OSPFv3 process ID (PID) 1 and area 0 on a given interface, the basic command is simply ipv6 ospf 1 area 0.Example of configuring OSPFv3: R(Config)#ipv6 unicast-routing R(Config)#int s0/0R(Config-if)#ipv6 address 2ffa::1/64 R(Config-if)#ipv6 ospf 1 area 0 R(Config-if)#ipv6 ospf priority <priority> R(Config-if)#ipv6 ospf cost <cost> QUESTION: 25 Company plans to migrate their network from IPv4 to IPv6 in the near future. Which three techniques can be used to transition from IPv4 to IPv6? (Select three) A. Dual stack B. NAT C. Flow label D. Mobile IP E. 6to4 tunneling F. Anycast G. MBGP Answer: A, B, E Explanation: The four key strategies for deploying IPv6 are as follows: Deploying IPv6 over IPv4 tunnels: These tunnels encapsulate the IPv6 traffic within the IPv4 packets, and are primarily for communication between isolated IPv6 sites or connection to remote IPv6 networks over an IPv4 backbone. The techniques include using manually configured tunnels, generic routing encapsulation (GRE) tunnels, semiautomatic tunnel mechanisms such as tunnel broker services, and fully automatic tunnel mechanisms such as IPv4- compatible and 6to4. Deploying IPv6 over dedicated data links:
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Slide 26: This technique enables isolated IPv6 domains to communicate by using the same Layer 2 infrastructure as for IPv4, but with IPv6 using separate FrameRelay or ATM PVCs, separate optical links, or dense Wave Division Multiplexing (dWDM). Deploying IPv6 over MPLS backbones: This technique allows isolated IPv6 domains to communicate with each other, but over an MPLS IPv4 backbone. Multiple techniques are available at different points in the network, but each requires little change to the backbone infrastructure or reconfiguration of the core routers because forwarding is based on labels rather than the IP header itself. Deploying IPv6 using dual-stack backbones: This technique allows IPv4 and IPv6 applications to coexist in a dual IP layer routing backbone. All routers in the network need to be upgraded to be dual stack with IPv4 communication using the IPv4 protocol stack and IPv6 communication using the IPv6stack.In addition to the strategies for deploying IPv6 within your IPv4 environment, you also need protocol translation mechanisms (for example, a NAT-PT device to connect IPv6-only web browsers to IPv4-only webservers) or dual- stack servers (for example, an e- mail server that handles IPv4-only and IPv6-only mail clients)to allow communication between applications using IPv4 and applications using IPv6. These mechanisms become increasingly important as IPv6 deployment moves from the testing to the actual usage phase, and more relevant as application developers decide that continuing to support IPv4 is not costeffective. Reference: http://www.cisco.com/en/US/tech/tk872/technologies_white_paper09186a00800c9907.sht ml#1098273
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