CCIE Routing and Switching FAQ: OSPF

ccie-routing-switching-faq-ospf

CCIE Routing and Switching FAQ: OSPF

Q1. R1 has received an OSPF LSU from R2. Which of the following methods can be used by R1 to acknowledge receipt of the LSU from R2?
A. TCP on R1 acknowledges using the TCP Acknowledgment field.

B. R1 sends back an identical copy of the LSU.

C. R1 sends back an LSAck to R2.

D. R1 sends back a DD packet with LSA headers whose sequence numbers match the sequence numbers in the LSU.

Answer: B and C

Q2. Fredsco has an enterprise network with one core Frame Relay connected router, with a hub-and-spoke network of PVCs connecting to ten remote offices. The network uses OSPF exclusively. The core router (R-core) has all ten PVCs defined under multipoint subinterface s0/0.1. Each remote router also uses a multipoint subinterface. Fred, the engineer, configures anip ospf network non-broadcast command under the subinterface on R-core and on the subinterfaces of the ten remote routers. Fred also assigns an IP address to each router from subnet 10.3.4.0/24, with R-core using the .100 address, and the remote offices using .1 through .10. Assuming that all other related options are using defaults, which of the following would be true about this network?
A. The OSPF hello interval would be 30 seconds.

B. The OSPF dead interval would be 40 seconds.

C. The remote routers could learn all routes to other remote routers’ subnets, but only if R-core became the designated router.

D. No designated router will be elected in subnet 10.3.4.0/24.

Answer: A and C

Q3. Which of the following interface subcommands, used on a multipoint Frame Relay subinterface, creates a requirement for a DR to be elected for the attached subnet?
A. ip ospf network point-to-multipoint
B. ip ospf network point-to-multipoint non-broadcast
C. ip ospf network non-broadcast
D. None of these answers is correct.

Answer: C

Q4. The following routers share the same LAN segment and have the stated OSPF settings: R1: RID 1.1.1.1, hello 10, priority 3; R2: RID 2.2.2.2, hello 9, priority 4; R3, RID 3.3.3.3, priority 3; and R4: RID 4.4.4.4, hello 10, priority 2. The LAN switch fails and recovers, and all routers attempt to elect an OSPF DR and form neighbor relationships at the same time. No other OSPF-related parameters were specifically set. Which of the following are true about negotiations and elections on this LAN?
A. R1, R3, and R4 will expect Hellos from R2 every 9 seconds.

B. R2 will become the DR but have no neighbors.

C. R3 will become the BDR.

D. R4’s dead interval will be 40 seconds.

E. All routers will use R2’s hello interval of 9 after R2 becomes the designated router.

Answer: B and D

Q5. Which of the following must be true for two OSPF routers that share the same LAN data link to be able to become OSPF neighbors?
A. Must be in the same area
B. Must have the same LSRefresh setting
C. Must have differing OSPF priorities
D. Must have the same Hello timer, but can have different dead intervals

Answer: A

Q6. R1 is an OSPF ASBR that injects an E1 route for network 200.1.1.0/24 into the OSPF backbone area. R2 is an ABR connected to area 0 and to area 1. R2 also has an Ethernet interface in area 0, IP address 10.1.1.1/24, for which it is the designated router, and has established OSPF adjacencies over this interface with other routers. R3 is a router internal to area 1. Enough links are up and working for the OSPF design to be working properly. Which of the following are true regarding this topology? (Assume that no other routing protocols are running, and that area 1 is not a stub area.)
A. R1 creates a type 7 LSA and floods it throughout area 0.

B. R3 will not have a specific route to 200.1.1.0/24.

C. R2 forwards the LSA that R1 created for 200.1.1.0/24 into area 1.

D. R2 will create a type 2 LSA for subnet 10.1.1.0/24 and flood it throughout area 0.

Answer: C and D

Q7. R1 is an OSPF ASBR that injects an E1 route for network 200.1.1.0/24 into the OSPF backbone area. R2 is an ABR connected to area 0 and to area 1. R2 also has an Ethernet interface in area 0, IP address 10.1.1.1/24, for which it is the designated router but there are no other OSPF routers on the segment. R3 is a router internal to area 1. Enough links are up and working for the OSPF design to be working properly. Which of the following are true regarding this topology? (Assume that no other routing protocols are running, and that area 1 is a totally NSSA.)
A. R3 could inject external routes into the OSPF domain.

B. R3 will not have a specific route to 200.1.1.0/24.

C. R2 forwards the LSA that R1 created for 200.1.1.0/24 into area 1.

D. R2 will create a type 2 LSA for subnet 10.1.1.0/24 and flood it throughout area 0.

Answer: A and B

Q8. The routers in area 55 all have thearea 55 stub no-summary command configured under therouter ospf command. OSPF has converged, with all routers in area 55 holding an identical link-state database for area 55. All IP addresses inside the area come from the range 10.55.0.0/16; no other links outside area 55 use addresses in this range. R11 is the only ABR for the area. Which of the following is true about this design?
A. The area is a stubby area.

B. The area is a totally stubby area.

C. The area is an NSSA.

D. ABR R11 is not allowed to summarize the type 1 and 2 LSAs in area 55 into the 10.55.0.0/16 prefix because of theno-summary keyword.

E. Routers internal to area 55 can have routes to specific subnets inside area 0.

F. Routers internal to area 55 can have routes to E1, but not E2, OSPF routes.

Answer: B

Q9. R1 is an OSPF ASBR that injects an E1 route for network 200.1.1.0/24 into the OSPF backbone area. R2 is an ABR connected to area 0 and to area 1. R2 also has an Ethernet interface in area 0, IP address 10.1.1.1/24, for which it is the designated router. R3 is a router internal to area 1. Enough links are up and working for the OSPF design to be working properly. Which of the following are true regarding this topology? (Assume that no other routing protocols are running, and that area 1 is not a stubby area.)
A. R3’s cost for the route to 200.1.1.0 will be the cost of the route as it was injected into the OSPF domain by R1, without considering any internal cost.

B. R3’s cost for the route to 200.1.1.0 will be the cost of reaching R1, plus the external cost listed in the LSA.

C. R3’s cost for the route to 10.1.1.0/24 will be the same as its cost to reach ABR R2.

D. R3’s cost for the route to 10.1.1.0/24 will be the sum of its cost to reach ABR R2 plus the cost listed in the type 3 LSA created for 10.1.1.0/24 by ABR R2.

E. It is impossible to characterize R3’s cost to 10.1.1.0/24 because R3 uses a summary type 3 LSA, which hides some of the costs.

Answer: B and D

Q10. R1 and R2 each connect through Fast Ethernet interfaces to the same LAN, which should be in area 0. R1’s IP address is 10.1.1.1/24, and R2’s is 10.1.1.2/24. The only OSPF-related configuration is as follows:

Which of the following statements are true about the configuration?
A. Thenetwork command on R2 does not match IP address 10.1.1.2, so R2 will not attempt to send Hellos or discover neighbors on the LAN.

B. The different process IDs in therouter ospf command will prevent the two routers from becoming neighbors on the LAN.

C. R2 will become the DR as a result of having a cost of 1 associated with its Fast Ethernet interface.

D. R1 and R2 could never become neighbors because of the difference in cost values.

E. R1’s OSPF cost for its Fast Ethernet interface would be 10.

Answer: A and E

Q11. Which of the following are true about setting timers with OSPF?
A. Theip ospf dead-interval minimal hello-multiplier 4 interface subcommand sets the hello interval to 4 ms.

b. Theip ospf dead-interval minimal hello-multiplier 4 interface subcommand sets the dead interval to 4 seconds.

C. Theip ospf dead-interval minimal hello-multiplier 4 interface subcommand sets the hello interval to 250 ms.

D. On all interfaces, theip ospf hello-interval 30 interface subcommand changes the hello interval from 10 to 30.

E. Theip ospf hello-multiplier 5 interface subcommand sets the dead interval to five times the then-current hello interval.

F. Cisco IOS defaults the hello and dead intervals to 30/120 on interfaces using the OSPF nonbroadcast network type.

Answer: C and F

Q12. R1 has been configured for OSPF authentication on its Fa0/0 interface as shown here. Which of the following is true about the configuration?

A. R1 will attempt simple-text authentication on the LAN with keyhannah .
B. R1 will attempt MD5 authentication on the LAN with keyjessie .
C. R1 will attempt OSPF type 2 authentication on Fa0/0.
D. R1 will attempt OSPF type 3 authentication on Fa0/0.

Answer: A

Q13. Which of the following statements about OSPFv3 are true?
A. Type 1 and 2 LSAs do not carry addressing information.
B. OSPFv3 messages are encapsulated directly into Layer 2 frames.
C. OSPFv3 uses 128-bit Router IDs.
D. There are three flooding scopes defined for OSPFv3 LSAs: link, area, and AS.
E. Multiple OSPFv3 instances can run over a single link.
F. OSPFv3 implements its own authentication mechanisms.

Answer: A, D, and E

Q14. Which statements are true about Link LSA and Intra-Area-Prefix LSA in OSPFv3?
A. Link LSAs have AS flooding scope.

B. Intra-Area-Prefix LSAs have area flooding scope.

C. Link LSAs carry information about link-local addresses.

D. Intra-Area-Prefix LSAs carry information about global prefixes.

E. When an updated Link or Intra-Area-Prefix LSA is flooded, a router is required to schedule a full SPF run.

F. Link and Intra-Area-Prefix LSAs have entirely replaced the Router and Network LSAs.

Answer: B, C, and D

15. How does OSPFv3 handle authentication?
A. OSPFv3 implements its own authentication and encryption mechanisms.

B. SSL/TLS is used by OSPFv3 to provide authentication and encryption.

C. OSPFv3 relies on IPsec to authenticate and encrypt its packets.

D. OSPFv3 makes use of ISAKMP/IKE protocols to negotiate authentication and encryption parameters between routers.

E. The use of AH and ESP is mutually exclusive in OSPFv3.

Answer: C and E

Q16. Which statements are true about address family support in OSPFv3?
A. When running multiple address families, a single link-state database on a router holds information from all address families.

B. Each address family is run as a separate OSPFv3 instance, keeping all its data and state separate.

C. Multiple address families are distinguished by separate OSPFv3 process IDs.

D. Running IPv4 and IPv6 address families simultaneously under a single OSPFv3 process will result in a significantly smaller memory footprint than running a separate IPv4 OSPFv2 and IPv6 OSPFv3 process.

E. Type 8 and 9 LSAs are reused to carry both IPv4 and IPv6 prefixes.

F. Even if running OSPFv3 for IPv4 address family, interfaces must be configured for IPv6 connectivity.

Answer: B, E, and F

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