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bandwidth of that interface. A higher bandwidth indicates a lower cost. There is more overhead
(higher cost) and time delays involved in crossing a 56k serial line than crossing a 10M ethernet
line. The formula used to calculate the cost is:
cost= 10000 0000/bandwith in bps
therefore 10000 0000 / 10000 0000 = 1
Reference:
http://www.cisco.com/warp/public/104/2.html
Q9
By what means is OSPF able to support VLSM?A. Uses route summarization.B. Maintains a topological database.C. Carries subnet mask information in the route updates.D. Allocates addresses in groups to support multiple areas.
Ans: C
Explanation: Each route update includes subnet mask information.
Incorrect Anss
A: VLSM allows route summarization, but VLSM does not use route summarization.
B: A topological database does not contain VLSM information.
D: This is not the way VLSM work.
Q0
Which of the following statements regarding OSPF's support of VLSM are true? (Select
two)A. A multiple area OSPF design dictates that VLSM be used throughout the AS.B. Summarization can be performed with different prefix lengths throughout the network.C. The use of VLSM enables a truly hierarchical addressing scheme to be developed.D. OSPF's support for VLSM does not compensate for its inability to handle discontiguous
subnets.
Ans: B, C
Explanation:
B: Summarization can be performed with different prefix lengths throughout the network, as
long as the ranges don't overlap.
C: VLSM enables a true hierarchical addressing scheme.
Reference: OSPF Design Guide
http://www.cisco.com/warp/public/104/3.html
Incorrect Anss
A: VLSM can be used locally only. VLSM is not required to be used throughout multiple areas.
D: In order to take advantage of summarization, network numbers in areas should be assigned in
a contiguous way to be able to lump these addresses into one range.
Q1
What is true about route summarization in OSPF?A. Type 3 and type 4 LSAs carry external summarized routes.B. Summarization prevents type 1 link LSAs from being propagated into the backbone
area0.C. Route summarization can be performed at any point in the network where enough
contiguous addresses are present.D. Route summarization reduces the amount of bandwidth, CPU, and memory resources
consumed by the OSPF process.
Ans: D
Explanation: Route summarization will increase performance by reducing the workload on the
router.
Q2
OSPF is a very scalable routing protocol, what are two reasons why? (Select two)A. Neighbor adjacencies control distribution of routing protocol updates.B. Routing table information does not flood the network until holddown timers have
expired.C. The hello protocol is a more efficient means of sending routing updates than table
exchange used in RIPv1.D. Topological database is maintained with incremental updates, with full exchange
occurring only every 30 minutes.
Ans: A, C
Explanation:
A: Adjacency refers to the relationship, which exists between a router and its DR/BDR. Neighbor
adjacencies control how updates are propagated.
C: The Hello Protocol used by OSPF to establish and maintain neighbor relationship.
Incorrect Anss
B, D: This is not related to the neighbor relationship.
Q3
You are the network engineer at CertKing . Your newly appointed CertKing trainee wants
to know what an OSPF router on an Ethernet segment will do when it sees a link-state
change.
What will your reply be?A. It broadcasts the LSA on each of its interfaces.B. It multicasts the link-state change to the DR and BDR.C. It immediately floods the change to all outer routers on the same segment.D. It updates its routing table, then floods the change to all other routers on the same
segment.
Ans: B
Explanation:
The steps for OSPF convergence are as follows:
1. When a router detects a link failure, the router sends an LSA to its neighbors. If the router is on
a multi-access link, it sends the update to the designated router (DR) and the backup designated router (BDR),
not to
all neighbors.
2. The path is removed from the originating router's tables.
3. On receipt of the LSA, all routers update the topology table and flood the LSA out its interfaces.
4. The routing protocol runs the Dijkstra algorithm to rebuild the routing table.
For OSPF, convergence is detection time, plus LSA flooding, plus 5 seconds before computing the topology
table.
This amounts to a few seconds.
Section 9: Describe the features and operation of multi-area OSPF (23 Questions)
Q 1
Which of the three areas below are valid OSPF areas? (Select three)A. stubB. activeC. remoteD. backboneE. ordinary or standard
Ans: A, D, E
Explanation:
There is no such thing as an 'active area' or a 'remote area' in OSPF. The correct OSPF area
types are
o ordinary area (a.k.a. standard area)
o stub area
o totally stubby area
o not so stubby area (a.k.a. NSSA)
o backbone area (a.k.a. area 0)
Q2
OSPF networks create Link State Advertisements (LSA). What kind of LSA is conceived
by an Area Border Router (ABR) containing route summarization of area subnets?A. Router link, type 1.B. Router summary link, type 8.C. Network summary link, type 3.D. AS external summary link, type 4.
Ans: C
Explanation: Network summary link entry, LSA type 3 is originated by ABRs. It describes the
links between the ABR and the internal routers of a local area. These entries are flooded
throughout the backbone area to the other ABRs.
Incorrect Anss
A: Router link, LSA type 1 is generated by each router for each area it belongs to. It describes
the states of the router's link to the area.
B, D: Do not apply here.
Q3
What kind of OSPF router has interfaces in two or more areas?A. ABRB. ASBRC. internal routerD. backbone router
Ans: A
Explanation: An ABR (Area Border Router) share an interface with at least one other OSPF
area.
Incorrect Anss
B: An ASBR (Autonomous System Border Router) have at least one interface in a non-OSPF
network.
C: An internal router is only connected to routers in the internal area.
D: A backbone router has at least one interface in the backbone, also known as Area 0.
Q4
When an OSPF ASBR announces external networks, what kind of LSA type does it use?A. Type 1 LSAB. Type 2 LSAC. Type 3 LSAD. Type 4 LSAE. Type 5 LSA
Ans: E
Explanation: In OSPF, Type 5 LSA is used to announce external networks.
Q5
Exhibit:
The status of external Network 22 has just changed. The router CertKing 5 uses a type 7
LSA to update area 1 of this change. In OSPF terminology, what kind of area is area 1
classified as?A. Backbone areaB. Transit areaC. Stubby areaD. Totally stubby areaE. Not-so-stubby area
Ans: E
Explanation:
o Stub Areas: These areas do not accept routes belonging to external autonomous systems
(AS); however, these areas have inter-area and intra-area routes. In order to reach the
outside networks, the routers in the stub area use a default route which is injected into the
area by the Area Border Router (ABR).
o Normal Areas: These areas can either be standard areas or transit (backbone) areas.
Standard areas are defined as areas that can accept intra-area, inter-area and external
routes.
o backbone area is the central area to which all other areas in OSPF connect.
o Totally Stub Areas: These areas do not allow routes other than intra-area and the default
routes to be propagated within the area. The ABR injects a default route into the area and
all the routers belonging to this area use the default route to send any traffic outside the
area.
o NSSA: This type of area allows the flexibility of importing a few external routes into the
area while still trying to retain the stub characteristic. Assume that one of the routers in
the stub area is connected to an external AS running a different routing protocol, it now
becomes the ASBR, and hence the area can no more be called a stub area. However, if
the area is configured as a NSSA, then the ASBR generates a NSSA external link-state
advertisement (LSA) (Type-7) which can be flooded throughout the NSSA area. These
Type-7 LSAs are converted into Type-5 LSAs at the NSSA ABR and flooded throughout
the OSPF domain
Reference:
http://www.cisco.com/en/US/tech/ CK3 65/ CK4 80/technologies_tech_note09186a0080094a74.shtml
Q6
What kind of information can you find a type 3 OSPF network summary link LSA?A. Summary of routes in the AS.B. Summary of link state sin an OSPF area.C. Summary of IP subnets in an OSPF area.D. Summary of metric coast from ABR to ASBR.
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