16 04 2014
Latest 2014 Pass4sure and Lead2pass Cisco 642-902 Practice Tests (81-90)
QUESTION 81
The 192.168.0.0 network is not being propagated throughout the network. Observe the BGP configuration commands from the advertising router. What is the reason the 192.168.0.0 route is not being advertised?
router bgp 65111
neighbor 172.16.1.1 remote-as 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
Select the best response.
A. The network 192.168.0.0 statement is missing mask 255.255.0.0
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 10.0.0.0 statement is missing mask 0.255.255.255.
E. The auto-summary configuration is missing.
Answer: A
Explanation:
The "network" statement in other routing protocols (EIGRP, OSPF, RIP…) is used to enable routing protocol on the interfaces within that "network" statement. But in BGP, the function of a network statement is to tell the router to search the IP routing table for a particular network, and if that network is found, originate it into the BGP database. But notice that you must have an exact match in the IP routing table to appear the network in the BGP routing table (in this case we don’t see the auto-summary command so we suppose it is disabled in this case). For example:+ network 10.10.10.0/8 will appear in BGP if network 10.10.10.0/8 appears in the IP routing table.+ network 10.10.10.0/24 will appear in BGP if network 10.10.10.0/24 appears in the IP routing table. Therefore, in this question the static route "ip route 192.168.0.0 255.255.0.0 null0 was used to put a route to 192.168.0.0/16 into the routing table (although it points to Null0 but this command really makes that route appears in the routing table). But the "network 192.168.0.0 statement tells the router to lookup network 192.168.0.0/24 (if the network statement under BGP-mode does not specify a subnet mask, the default subnet mask of that class will be used). The router only finds network 192.168.0.0/16 -> The network 192.168.0.0 is not being propagated throughout the network because of the mismatch of the subnet mask.
Just for your information, in fact we have to suppose there is no entry of the network 192.168.0.0/24 exist in the routing table except the static route "ip route 192.168.0.0 255.255.0.0 null0. If such an entry exists (for example, a directly connected entry like "C 192.168.0.0/24 is directly connected") then the router still advertises it with the "network 192.168.0.0 (without mask
255.255.0.0) command.
QUESTION 82
Which BGP attribute is used by BGP to prevent routing loops? Select the best response.
A. AS-path
B. next-hop
C. MED
D. weight
E. local preference
F. origin
Answer: A
Explanation:
The AS-PATH attribute is used to prevent BGP routing loops. When receiving an BGP advertisement, the router checks the AS-PATH attribute, if it see it’s own AS number in the AS- Path then it is a routing loop so the router will not install this route in its BGP table.
QUESTION 83
Which BGP path attribute is Cisco proprietary? Select the best response.
A. weight
B. MED
C. local preference
D. origin
E. next-hop
F. AS-path
Answer: A
Explanation:
The weight attribute is a Cisco proprietary technology. This attribute is local to a router and is not advertised to neighboring routers. If the router learns about more than one route to the same destination, the route with the highest weight will be preferred and will be installed in the routing table. By default, the value of weight is 0 and the range is from 0 to 65535. The route with the highest weight will be installed in the IP routing table.
QUESTION 84
Which show command will display only the Type 5 LSAs in the OSPF topology database? Select the best response.
A. show ip route
B. show ip route ospf
C. show ip ospf database summary
D. show ip ospf database nssa-external
E. show ip ospf database external
Answer: E
Explanation:
The "show ip ospf database external" command displays information only about external LSAs (Type 5 LSAs).
Below is an example of the "show ip ospf database external" command Notice the line "LS Type: AS External Link", which means LSA Type 5. For your information, the "Link State ID: 143.105.0.0 indicates the network being advertised; the "Advertising Router:
10.187.70.6 indicates the router that originated this LSA.
Note:
+ The "show ip ospf database summary" command displays information only about the summary LSAs. + The "show ip ospf database nssa-external" command displays information only about the not so stubby area (NSSA) external LSAs.
QUESTION 85
Which command will display EIGRP packets sent and received, as well as statistics on hello packets, updates, queries, replies, and acknowledgments? Select the best response.
A. debug eigrp packets
B. show ip eigrp traffic
C. debug ip eigrp
D. show ip eigrp interfaces
Answer: B
Explanation:
The show ip eigrp traffic command displays the number of Enhanced IGRP (EIGRP) packets sent and received.
QUESTION 86
Which three statements are true about EIGRP operation? (Choose three.)
A. When summarization is configured, the router will also create a route to null 0.
B. The summary route remains in the route table, even if there are no more specific routes to the
network.
C. Summarization is configured on a per-interface level.
D. The maximum metric for the specific routes is used as the metric for the summary route.
E. Automatic summarization across major network boundaries is enabled by default.
Answer: ACE
QUESTION 87
Which three are advantages to creating multiple areas in OSPF? (Choose three.)
A. less frequent SPF calculations
B. fewer hello packets
C. smaller routing tables
D. reduced LSU overhead
E. fewer adjacencies needed
Answer: ACD
Explanation:
OSPF routers within an area only need to know about other routers within their own area, not outside their area, and all OSPF routers within a given area share the same link state database. This keeps the routing tables small enough to prevent processing bottlenecks from occurring. Also SPF only needs to calculate paths to routers within that area. If a router receives an LSA with old information then it will send a LSU to the sender to update the sender with the newer information. The Link State Update (LSU) holds the LSAs. Instead of sending multiple LSUs the ABR / ASBR summarizes a route and sends only one LSU-.
Note: The LSA has a 30 minute timer that causes the router to send an LSU to everyone on the network once it ages out.
QUESTION 88
Which two statements about the EIGRP DUAL process are correct? (Choose two.)
A. An EIGRP route will go active if there are no successors or feasible successors in the EIGRP
topology table.
B. An EIGRP route will go passive if there are no successors in the EIGRP topology table.
C. DUAL will trigger an EIGRP query process while placing the flapping routes in the holddown
state.
D. A feasible successor in the EIGRP topology table can become the successor only after all the
query requests have been replied to.
E. The stuck in active state is caused when the wait for the query replies have timed out.
F. EIGRP queries are sent during the loading state in the EIGRP neighbor establishment process.
Answer: AE
Explanation:
http://routemyworld.com/category/routing-protocols/eigrp/
QUESTION 89
What are three key concepts that apply when configuring the EIGRP stub routing feature in a hub and spoke network? (Choose three.)
A. A hub router prevents routes from being advertised to the remote router.
B. Only remote routers are configured as stubs.
C. Stub routers are not queried for routes.
D. Spoke routers connected to hub routers answer the route queries for the stub router.
E. A stub router should have only EIGRP hub routers as neighbors.
F. EIGRP stub routing should be used on hub routers only.
Answer: BCE
Explanation:
http://astorinonetworks.com/2011/06/14/eigrp-stub-routing/
http://www.cisco.com/en/US/docs/ios/12_0s/feature/guide/eigrpstb.html
QUESTION 90
Which attribute must exist in the BGP update packet? Select the best response.
A. LOCAL_ PREF
B. AGGREGATOR
C. AS_Path
D. Weight
Answer: C
Explanation:
Origin, AS_Path, Next_Hop are well-known mandatory BGP attributes that all BGP Updates must include.
Note:
There are 4 BGP attribute types:
+ Well-known Mandatory: recognized by all implementations of BGP and must appear in a BGP update message. If missing, a notification error will be generated.+ Well-Known Discretionary:
recognized by all implementations of BGP but may not be sent in the BGP update message (include LOCAL_PREF, ATOMIC_AGGREGATOR).+ Optional Transitive: may or may not be recognized by all BGP implementations. Because the attribute is transitive, BGP accepts and advertises the attribute even if it is not recognized (include Community attribte).+ Optional Nontransitive: may or may not be recognized by all BGP implementations. Whether or not the receiving BGP router recognizes the attribute, it is nontransitive and is not passed along to other BGP peers (include MED).
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