OSPF Interview Questions & Answers

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OSPF Interview Questions and  Answers Vol 1.0

Questions : 100

Check the complete list of questions:

Get equipped with the best set of questions asked for OSPF :

1. Why are loopbacks advertised as /32 host routes in OSPF ?
2. How do I change the reference bandwidth in OSPF ?
3. How does OSPF calculate its metric or cost ?
4. What algorithm is used by OSPF if equal cost routes exist ?
5. Are OSPF routing protocol exchanges authenticated ?
6. What is the link-state retransmit interval, and what is the command to set it ?
7. Is it true that only the static option of the virtual link in OSPF allows discontiguous networks, regardless of the mask propagation properties ?
8. Does the Cisco OSPF support IP TOS-based routing?
9. Does the offset-list subcommand work for OSPF ?
10. Can an OSPF default be originated into the system based on external information on a router that does not itself have a default ?
11. Can I use the distribute-list in/out command with OSPF to filter routes ?
12. How can I give preference to OSPF inter-area routes over intra-area routes ?
13. When routes are redistributed between OSPF processes, are all shortest path first algorithm  metrics preserved, or is the default metric value used ?
14. Which address-wild-mask pair should I use for assigning an unnumbered interface to an area ?
15. Can we have one numbered and other side unnumbered in OSPF ?
16. What is the reason for receiving “unknown routing protocol” error message when I configure “Router OSPF One” ?
17. What do the states DR, BDR, and DROTHER mean in show ip ospf interface command output ?
18. Why do I not see OSPF neighbors as FULL/DR or FULL/BDR on my serial link ?
19. Do I need any special commands to run OSPF over asynchronous links?
20. Which Cisco IOS Software release began support for per-interface authentication type in OSPF?
21. Can I control the P-bit when importing external routes into a not-so-stubby area (NSSA) ?
22. Why does OSPF show commands respond so slow ?
23. What does the clear ip ospf redistribution command do ?
24. How often does OSPF send out link-state advertisements (LSAs) ?
25. How do I stop individual interfaces from developing adjacencies in an OSPF network ?
26. When I have two type 5 link-state advertisements (LSAs) for the same external network in the OSPF database, which path should be installed in the IP routing table ?
27. Why is it that my Cisco 800 router does not run OSPF ?
28. Should I use the same process number while configuring OSPF on multiple routers within the same network?
29. I have a router that runs Cisco Express Forwarding (CEF) and OSPF, who does load-balancing when there are multiple links to a destination?
30. How does OSPF use two Multilink paths to transfer packets ?
31. How can you detect the topological changes rapidly?
32. Does the 3825 Series Router support the OSPF Stub feature?
33. What does the error message %OSPF-4-FLOOD_WAR: Process process-id re-originates LSA ID ip address type-2 adv-rtr ip address in area area id means?
34. Can we have OSPF run over a GRE tunnel ?
35. Is there a way to manipulate and prefer the Type 3 LSAs to originate from two different areas sent to the non-backbone area ?
36. What is the purpose of the “variable IP-OSPF-Transmit-Delay” ?
37. Is there a drop/flap of an OSPF neighborship when changing an OSPF area type from “nssa no-summary” to “nssa” ?
38. In the %OSPF-5-ADJCHG: Process ID, Nbr [ip address] on Port-channel31 from FULL to EXSTART, SeqNumberMismatch error message, what does SeqNumberMismatch signify ?
39. What is the maximum number of OSPF processes (VRF aware) on 7600/6500 platforms?
40. How does ISPF impact or improve the OSPF network?
41. Is there a way to compare Cisco NX-OS/IOS OSPF commands ?
42. Is there any feature of OSPF protocol for quick convergence and a slow re-convergence of routes ?
43. What are different neighbor states in OSPF ?
44. Give the command for defining the cost of a default route propagated into an area?
45. What is role of topology and routing table in OSPF ?
46. When I issue the “show ip ospf neighbor” command, why do I only see FULL/DR and FULL/BDR, with all other neighbors showing 2-WAY/DROTHER ?
47. Name types of LSA ?
48. Why do I receive the “cannot allocate router id” error message when I configure Router OSPF One ?
49. What are the different OSPF network types and give an example for each ?
50. What command would you use to create a totally stubby area?
51. Name tables which OSPF maintain ?
52. Which multicast addresses used in OSPF ?
53. On which router is the area default cost defined ?
54. With which network type will OSPF establish router adjacencies but not perform the DR/BDR election process?
55. What are the Route types in OSPF ?
56. What is the administrative distance of OSPF ?
57. What is the value of hello and Dead timers in OSPF ?
58. What are the Area Types ?
59. What are the different States in OSPF?
60. What must match before an adjacency ?
61. How to perform Inter-Area Summarization in OSPF ?
62. How to perform External Summarization ?
63. What are Virtual-Links ?
64. What is need of virtual Link ?
65. What is a Sham-Link ?
66. Explain the following syntax and what it will achieve: area 1 stub no-summary ?
67. What could be reason for OSPF neighbors being “stuck in 2 way” ?
68. What could be reason for OSPF neighbors being “stuck in Extart” ?
69. What could be reason for OSPF neighbors being “stuck in init” ?
70. What could be reason for OSPF neighbors being “stuck in loading” ?
71. What is the algorithm used by OSPF ?
72. What is OSPF Router ID and how is it elected ?
73. What is the DR/BDR in OSPF? How these are elected and in what scenario ?
74. What will happen if we make priority of a OSPF router as “zero” ?
75. Does DR/BDR election happen in OSPF Point to Point Network  ?
76. What is Backbone area ?
77. What is stub area, Totally Stubby Area, Not So Stubby area (NSSA)?
78. Can area 1 and area 2 exchange or advertise networks if they are not connected to area 0 (Backbone area) ? What we need to do make it happen ?
79. Explain the concept of Area Border Router (ABR) ?
80. Explain concept of Autonomous System Border Router (ASBR) ?
81. What is O E1, O E2 letters in OSPF? Which is default external type 1 or external type 2 ?
82. If any of the OSPF area is not stabilized, does it impact another area ?
83. What is OSPF routes preference in order for the following list – External Type 2 (E2) , Intra-Area (O), External Type 1 (E1), NSSA Type 1 (N1), Inter-Area (O IA), NSSA Type 2 (N2) ?
84. What is benefit of dividing network into areas ?
85. What parameters must match for 2 routers to become neighbors ?
86. What are various OSPF states?
87. Does OSPF form adjacencies with neighbors that are not on the same subnet ?
88. Explain OSPF LSA, LSU and LSR ?
89. What is difference between OSPF and EIGRP ?
90. What is difference between OSPF and IS-IS ?
91. Provide the 3 table types in OSPF ?
92. Is OSPF a classless or classfull protocol?
93. Which protocol does OSPF uses at the transport layer for communication ?
94. Can we use OSPF without backbone area?
95. Which RFC describes OSPF version 2 ?
96. By default OSPF will load balance over how many equal cost paths ?
97. OSPF is represented as protocol number _____ in the IP packet
98. Which are the 2 main functions of the DR ?
99. Which 2 parameters assist in DR election?
100. How to advertise a default-route if it doesn’t exist in the RIB?