11 04 2014
Latest 2014 Pass4sure and Lead2pass Cisco 642-902 Practice Tests (41-50)
QUESTION 41
When an OSPF design is planned, which implementation can help a router not have memory resource issues? Select the best response.
A. Have a backbone area (area 0) with 40 routers and use default routes to reach external destinations.
B. Have a backbone area (area 0) with 4 routers and 30,000 external routes injected into OSPF.
C. Have less OSPF areas to reduce the need for interarea route summarizations.
D. Have multiple OSPF processes on each OSPF router. Example, router ospf 1, router ospf 2
Answer: A
Explanation:
Memory issues usually come up when too many external routes are injected in the OSPF domain. A backbone area with 40 routers and a default route to the outside world would have less memory issues compared with a backbone area with 4 routers and 33,000 external routes being injected into OSPF. Router memory could also be conserved by using a good OSPF design. Summarization at the area border routers and use of stub areas could further minimize the number of routes exchanged.
The total memory used by OSPF is the sum of the memory used in the routing table ( show ip route summary ) and the memory used in the LSDB. The following numbers are a "rule of thumb" estimate. Each entry in the routing table will consume between approximately 200 and 280 bytes plus 44 bytes per extra path. Each LSA will consume a 100 byte overhead plus the size of the actual LSA, possibly another 60 to 100 bytes (For router links, this depends on the number of interfaces on the router). These amounts should be added to memory already used by other processes and by the IOS itself.
If you really want to know the exact number, you can do a show memory with and without OSPF being turned on. The difference in the processor memory used would be the answer.
QUESTION 42
The maximum number of routers per OSPF area typically depends on which three factors? (Choose three.)
A. the kind of OSPF areas being implemented
B. the number of external LSAs in the network
C. the number of DRs and BDRs in the areas
D. the number of virtual links in the areas
E. how well the areas can be summarized
F. the use of LSA filters
Answer: ABE
QUESTION 43
You are troubleshooting an OSPF problem where external routes are not showing up in the OSPF database Which two options are valid checks that should be performed first to verify proper OSPF operation? (Choose two.)
A. Are the ASBRs trying to redistribute the external routes into a totally stubby area?
B. Are the ABRs configured with stubby areas?
C. Is the subnets keyword being used with the redistribution command?
D. Is backbone area (area 0) contiguous?
E. Is the CPU utilization of the routers high?
Answer: AC
Explanation:
A totally stubby stubby area cannot have an ASBR so it will discard this type of LSA (LSA Type 5) -> A is a valid check.
Each stubby area needs an ABR to communicate with other areas so it is normal -> B is not a valid check.
When pulling routes into OSPF, we need to use the keyword "subnets" so that subnets will be redistributed too. For example, if we redistribute these EIGRP routes into OSPF:
+ 10.0.0.0/8+ 10.10.0.0/16+ 10.10.1.0/24
without the keyword "subnets"
router ospf 1redistribute eigrp 1
Then only 10.0.0.0/8 network will be redistributed because other routes are not classful routes, they are subnets. To redistribute subnets we must use the keyword "subnets" router ospf 1redistribute eigrp 1 subnets
-> C is a valid check.
We don’t need to care if area 0 is contiguous or not -> D is not a valid check. CPU utilization cannot be the cause for this problem -> E is not a valid check.
QUESTION 44
When verifying the OSPF link state database, which type of LSAs should you expect to see within the different OSPF area types? (Choose three.)
A. All OSPF routers in stubby areas can have type 3 LSAs in their database.
B. All OSPF routers in stubby areas can have type 7 LSAs in their database.
C. All OSPF routers in totally stubby areas can have type 3 LSAs in their database.
D. All OSPF routers in totally stubby areas can have type 7 LSAs in their database.
E. All OSPF routers in NSSA areas can have type 3 LSAs in their database.
F. All OSPF routers in NSSA areas can have type 7 LSAs in their database.
Answer: AEF
QUESTION 45
When verifying OSPF virtual link problems, which is an important item to check on the two transit OSPF routers? Select the best response.
A. OSPF process ID
B. OSPF router ID
C. OSPF network type
D. OSPF memory usage
E. OSPF CPU utilization
F. OSPF stub area configurations
Answer: B
Explanation:
The OSPF router IDs of the two transit OSPF routers are used to form the virtual link (with the area area-id virtual-link neighbor-router-id command) so it is an important item to check -> B is correct.
QUESTION 46
You are developing a verification plan for an upcoming OSPF implementation. Part of this plan is to verify the status of type 3 LSAs within the network. Which routers should you verify first to ensure that the configurations are correct for generating type 3 LSAs?
Select the best response.
A. Internal routers within the backbone area (area 0)
B. Internal routers within the NSSAs
C. Internal routers within the stubby areas
D. ASBRs
E. ABRs
F. DRs and BDRs
Answer: E
Explanation:
Type 3 LSA (Summary LSA) is advertised by the ABR of originating area to advertise network from other areas so we should check the ABRs first.
QUESTION 47
Which condition must be satisfied before an EIGRP neighbor can be considered a feasible successor? Select the best response.
A. The neighbor’s advertised distance must be less than or equal to the feasible distance of the
current successor.
B. The neighbor’s advertised distance must be less than the feasible distance of the current successor.
C. The neighbor’s advertised distance must be greater than the feasible distance of the current
successor.
D. The neighbor’s advertised distance must be equal to the feasible distance of the current successor.
E. The neighbor’s advertised distance must be greater than or equal to the feasible distance of
the current successor.
Answer: B
Explanation:
The feasible successor route is a route which has a higher metric than the successor route to reach a subnet but meets the feasibility condition and can be used in the event that the successor route goes down. This route does NOT get installed in the routing table but is kept in the topology table. The feasibility condition states that the AD from a neighbor must be less than the metric of the successor route (the feasible distance [FD]) because routing through a feasible successor when the AD > FD may cause a routing loop.
QUESTION 48
Based on the need to limit processing and bandwidth utilization due to dynamic routing protocol operation, the following routing requirements have been specified for your network.
– partial and incremental routing updates
– only the devices affected by a topology change perform route recomputation
– route recomputation only occurs for routes that were affected
Which dynamic routing protocol should be deployed in your network to best meet these requirements? Select the best response.
A. BGP
B. OSPF
C. IS-IS
D. EIGRP
E. RIPv2
Answer: D
Explanation:
The bandwidth utilization issue has been addressed by implementing partial and incremental updates. Therefore, only when a topology change occurs does routing information get sent. Regarding processor utilization, the feasible successor technology greatly reduces the total processor utilization of an AS by requiring only the routers that were affected by a topology change to perform the route recomputation. Furthermore, the route recomputation only occurs for routes that were affected. Only those data structures are accessed and used. This greatly reduces search time in complex data structures.
QUESTION 49
Which statement about a non-zero value for the load metric (k2) for EIGRP is true? Select the best response.
A. A change in the load on an interface will cause EIGRP to recalculate the routing metrics and send
a corresponding update out to each of its neighbors.
B. EIGRP calculates interface load as a 5-minute exponentially weighted average that is updated every
5 minutes.
C. EIGRP considers the load of an interface only when sending an update for some other reason.
D. A change in the load on an interface will cause EIGRP to recalculate and update the administrative
distance for all routes learned on that interface.
Answer: C
Explanation:
The load metric (k2) represents the worst load on a link between source and destination. EIGRP routing updates are triggered only by a change in network topology (like links, interfaces go up/down, router added/removed), and not by change in interface load or reliability. The load is a five minute exponentially weighted average that is updated every five seconds (not five minutes) .
EIGRP considers the load of an interface only when sending an update for some other reason (like a link failure)
QUESTION 50
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? Select the best response.
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.
Answer: D
Explanation:
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.
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