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71.
R1 is internal to area 1, and R2 is internal to area 2. Subnet 10.1.1.0/24 exists in area 2
as a connected subnet off R2. ABR1 connects area 1 to backbone area 0, and ABR2
connects area 0 to area 2. Which of the following LSAs must R1 use when calculating
R1's best route for 10.1.1.0/24?
- A.R2 's Type 1 LSA
- B.Subnet 10.1.1.0/24's Type 2 LSA
- C.ABR1’s Type 1 LSA in area 0
- D.Subnet 10.1.1.0/24's Type 3 LSA in Area 0
- E.Subnet 10.1.1.0/24's Type 3 LSA in Area 1
- Answer & Explanation
- Report
Answer : [E]
Explanation :
Explanation :
| R1, internal to area 1, can use LSAs only in the area 1 LSDB. R2's Type 1 LSA exists only in area 2's LSDB. The Type 2 LSA for subnet 10.1.1.0/24, if one exists, also only exists in area 2's LSDB. R1 will use ABR1’s Type 1 LSA in area 1 to calculate the possible intra-area routes inside area 1, but R1 will use ABR1’s Type 1 LSA in area 1. Finally, the Type 3 LSA, created for 10.1.1.0/24 and flooded into area 1, is also needed to calculate the metric. |
72.
Which of the following LSA types describe topology information that, when changed,
requires a router in the same area to perform an SPF calculation? (Choose two.)
- A.1
- B.2
- C.3
- D.4
- E.5
- F.7
- Answer & Explanation
- Report
Answer : [A and B]
Explanation :
Explanation :
| OSPF builds the SPF tree based on the topology information in Type 1 and Type 2 LSAs. Changes therefore require another SPF run. Changes to the other LSA types do not require an SPF calculation. |
73.
The following output was taken from Router R3. A scan of R3's configuration shows
that no bandwidth commands have been configured in this router. Which of the following
answers list configuration settings that could be a part of a configuration that
results in the following output? Note that only two of the three interface’s costs have
been set directly. (Choose two.)
R3# show ip ospf interface brief Interface PID Area IP Address/Mask Cost State Nbrs F/C Se0/0/0.2 3 34 10.10.23.3/29 647 P2P 1/1 Se0/0/0.1 3 34 10.10.13.3/29 1000 P2P 1/1 Fa0/0 3 34 10.10.34.3/24 20 BDR 1/1
- A.An auto-cost reference-bandwidth 1000 command in router ospf mode
- B.An auto-cost reference-bandwidth 2000 command in router ospf mode
- C.An ip ospf cost 1000 interface S0/0/0.1 command in router ospf mode
- D.An auto-cost reference-bandwidth 64700 command in router ospf mode
- Answer & Explanation
- Report
Answer : [A and B]
Explanation :
Explanation :
|
Because none of the interfaces have a bandwidth command configured,
the only commands that can influence the OSPF cost are the auto-cost referencebandwidth
router subcommand and the ip ospf cost interface subcommand. To give
the output shown in the question, the interface cost could be set directly on all three
interfaces listed. Alternatively, the reference bandwidth could be set (in router configuration
mode) to cause one of the interface costs to be as shown in the output,
with the other two interfaces having their costs set directly. For the wrong answers, the ip ospf cost interface s0/0/0.1 router subcommand does not exist—instead, it is an interface subcommand. An auto-cost of 64700, used as the numerator in the ref-bw/bandwidth cost calculation, does not result in any of the three listed interface costs. For the two correct answers, with a default bandwidth of 1544 (kbps) on the serial subinterfaces, a reference bandwidth of 1000 (Mbps) implies the math 1,000,000 / 1544, for an interface cost of 647. With a default bandwidth of 100,000 kbps (100 Mbps) on Fa0/0, a reference bandwidth of 2000 (Mbps) implies math of 2000 / 100 = 20. |
74.
Router B1, an internal router in area 1, displays the following output. The only two
ABRs connected to area 1 are performing Type 3 LSA filtering. Which of the following
answers is true based on the information in the output from B1?
R1# show ip route 10.1.0.0 255.255.0.0 longer-prefixes ! Legend lines omitted for brevity 10.0.0.0/8 is variably subnetted, 17 subnets, 3 masks O 10.1.2.0/24 [110/658] via 10.10.13.1, 00:00:32, Serial0/0/0.1 O IA 10.1.1.0/24 [110/658] via 10.10.23.2, 00:41:39, Serial0/0/0.2 O IA 10.1.3.0/24 [110/658] via 10.10.23.2, 00:41:39, Serial0/0/0.2
- A.A Type 3 LSA for 10.2.2.0/24 was filtered by both ABRs.
- B.A Type 3 LSA for 10.1.2.0/24 was not filtered by both ABRs
- C.A Type 3 LSA for 10.1.2.0/24 was not filtered by both ABRs
- D.A Type 3 LSA for 10.1.1.0/24 was filtered by both ABRs.
- Answer & Explanation
- Report
Answer : [C]
Explanation :
Explanation :
|
The output lists all of B1’s routes for subnets within the range 10.1.0.0–
10.1.255.255 whose prefix lengths are longer than /16. One answer lists subnet
10.2.2.0/24, which is not in this range, so the output cannot be used to confirm
or deny whether the subnet was filtered. B1’s route for 10.1.2.0/24 is an intra-area
route by virtue of not listing an inter-area (IA) code by the route. Type 3 LSA filtering only filters Type 3 LSAs, which routers use to calculate interarea routes, so the output tells us nothing about any filtering of 10.1.2.0/24. The output shows a single interarea route for 10.1.3.0/24, so at least one ABR has flooded a Type 3 LSA for this route. Additionally, the output confirms that at least one ABR flooded a Type 3 LSA for 10.1.3.0/24, or the output would not show an IA route for 10.1.3.0/24. So, the Type 3 LSA for 10.1.3.0/24 was not filtered by both ABRs. |
75.
The following command output was gathered from Router R1, an ABR between area
0 (backbone) and area 1. In this internetwork, area 0 contains all the subnets of Class
A network 10.0.0.0. R1’s OSPF process has a distribute list configured. Assuming
that the subnets listed in the answers actually exist in area 0, which of the following
occurs on Router R1?
R1# sh ip prefix-list ip prefix-list question: 3 entries seq 5 deny 10.1.2.0/24 ge 25 le 27 seq 15 deny 10.2.0.0/16 ge 30 le 30 seq 20 permit 0.0.0.0/0 le 32
- A.R1 will not create/flood a Type 3 LSA for subnet 10.1.2.0/26 into area 1.
- B.R1 will not create/flood a Type 3 LSA for subnet 10.1.2.0/24 into area 1.
- C.R1 will not have an OSPF route for subnet 10.1.2.0/26 in its IP routing table.
- D.R1 will not have an OSPF route for subnet 10.1.2.0/24 in its IP routing table
- Answer & Explanation
- Report
Answer : [C]
Explanation :
Explanation :
|
When referenced from a distribute list, OSPF filters routes from being added to
that router's IP routing table but has no impact on the flow of LSAs. As such, neither
A nor B is correct. An OSPF distribute-list command does attempt to filter routes
from being added to the IP routing table by OSPF, so the two answers that mention
the IP routing table might be correct. Sequence number 5 matches prefixes from 10.1.2.0 through 10.1.2.255, with prefix lengths in the range 25–27, and denies (filters) those prefixes. So, the prefix list will match 10.1.2.0/26 with the first line, with a deny action. The 10.1.2.0/24 subnet does not match the first line of the prefix list, but it does match the third line, the match all line, with a permit action. Because 10.1.2.0/26 is matched by a deny clause, this route is indeed filtered, so it is not added to R1’s IP routing table. 10.1.2.0/24, matched with a permit clause, is allowed and would be in the IP routing table. |
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