Top 100++ OSPF (CCNA, CCNP & CCIE ) Interview Questions
1 What is OSPF?
2 What Is Backbone Area?
3 Why and on what environment do we implement OSPF?
4 Mention some characteristics of OSPF?
5 Why are loopbacks advertised as /32 host routes in OSPF?
6 How do I change the reference bandwidth in OSPF?
7 How does OSPF calculate its metric or cost ?
8 What is the reason for receiving “unknown routing protocol” error message when I configure “Router OSPF One” ?
9 What do the states DR, BDR, and DROTHER mean in show ip ospf interface command output ?
10 Why do I not see OSPF neighbors as FULL/DR or FULL/BDR on my serial link ?
11 Can I control the P-bit when importing external routes into a not-so-stubby area (NSSA) ?
12 Why does OSPF show commands respond so slow ?
13 What does the clear ip ospf redistribution command do ?
14 How often does OSPF send out link-state advertisements (LSAs) ?
15 How do I stop individual interfaces from developing adjacencies in an OSPF network ?
16 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 ?
17 Why is it that my Cisco 800 router does not run OSPF ?
18 What algorithm is used by OSPF if equal cost routes exist ?
19 Are OSPF routing protocol exchanges authenticated ?
20 What is the link-state retransmit interval, and what is the command to set it ?
21 Is it true that only the static option of the virtual link in OSPF allows discontiguous networks, regardless of the mask propagation properties ?
22 Does the Cisco OSPF support IP TOS-based routing?
23 Does the offset-list subcommand work for OSPF ?
24 Can an OSPF default be originated into the system based on external information on a router that does not itself have a default ?
25 Can I use the distribute-list in/out command with OSPF to filter routes ?
26 How can I give preference to OSPF inter-area routes over intra-area routes ?
27 When routes are redistributed between OSPF processes, are all shortest path first algorithm metrics preserved, or is the default metric value used ?
28 Which address-wild-mask pair should I use for assigning an unnumbered interface to an area ?
29 Can we have one numbered and other side unnumbered in OSPF ?
30 I have a router that runs Cisco Express Forwarding (CEF) and OSPF, who does load-balancing when there are multiple links to a destination?
31 How does OSPF use two Multilink paths to transfer packets ?
32 How can you detect the topological changes rapidly?
33 Does the 3825 Series Router support the OSPF Stub feature?
34 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?
35 Can we have OSPF run over a GRE tunnel ?
36 Is there a way to manipulate and prefer the Type 3 LSAs to originate from two different areas sent to the non-backbone area ?
37 What is the purpose of the “variable IP-OSPF-Transmit-Delay” ?
38 Is there a drop/flap of an OSPF neighborship when changing an OSPF area type from “nssa no-summary” to “nssa” ?
39 In the %OSPF-5-ADJCHG: Process ID, Nbr [ip address] on Port-channel31 from FULL to EXSTART, SeqNumberMismatch error message, what does SeqNumberMismatch signify ?
40 What is the maximum number of OSPF processes (VRF aware) on 7600/6500 platforms?
41 How does ISPF impact or improve the OSPF network?
42 Is there a way to compare Cisco NX-OS/IOS OSPF commands ?
43 Is there any feature of OSPF protocol for quick convergence and a slow re-convergence of routes ?
44 What are different neighbor states in OSPF ?
45 Give the command for defining the cost of a default route propagated into an area?
46 What is role of topology and routing table in OSPF ?
47 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 ?
48 Name types of LSA ?
49 Why do I receive the “cannot allocate router id” error message when I configure Router OSPF One ?
50 What are the different OSPF network types and give an example for each ?
51 What command would you use to create a totally stubby area?
52 Name tables which OSPF maintain ?
53 Which multicast addresses used in OSPF ?
54 On which router is the area default cost defined ?
55 With which network type will OSPF establish router adjacencies but not perform the DR/BDR election process?
56 What are the Route types in OSPF ?
57 What is the administrative distance of OSPF ?
58 What is the value of hello and Dead timers in OSPF ?
59 What are the Area Types ?
60 What are the different States in OSPF?
61 What must match before an adjacency ?
62 How to perform Inter-Area Summarization in OSPF ?
63 How to perform External Summarization ?
64 What are Virtual-Links ?
65 What is need of virtual Link ?
66 What is a Sham-Link ?
67 Explain the following syntax and what it will achieve: area 1 stub no-summary ?
68 What could be reason for OSPF neighbors being “stuck in 2 way” ?
69 What could be reason for OSPF neighbors being “stuck in Extart” ?
70 What could be reason for OSPF neighbors being “stuck in init” ?
71 What could be reason for OSPF neighbors being “stuck in loading” ?
72 What is the algorithm used by OSPF ?
73 What is OSPF Router ID and how is it elected ?
74 What is the DR/BDR in OSPF? How these are elected and in what scenario ?
75 What will happen if we make priority of a OSPF router as “zero” ?
76 Does DR/BDR election happen in OSPF Point to Point Network ?
77 What is Backbone area ?
78 What is stub area, Totally Stubby Area, Not So Stubby area (NSSA)?
79 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 ?
80 Explain the concept of Area Border Router (ABR) ?
81 Explain concept of Autonomous System Border Router (ASBR) ?
82 What is O E1, O E2 letters in OSPF? Which is default external type 1 or external type 2 ?
83 If any of the OSPF area is not stabilized, does it impact another area ?
84 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) ?
85 What is benefit of dividing network into areas ?
86 What parameters must match for 2 routers to become neighbors ?
87 What are various OSPF states?
88 Does OSPF form adjacencies with neighbors that are not on the same subnet ?
89 Explain OSPF LSA, LSU and LSR ?
90 Provide the 3 table types in OSPF ?
91 Is OSPF a classless or classfull protocol?
92 Which protocol does OSPF uses at the transport layer for communication ?
93 Can we use OSPF without backbone area?
94 Which RFC describes OSPF version 2 ?
95 By default OSPF will load balance over how many equal cost paths ?
96 Which are the 2 main functions of the DR ?
97 Which 2 parameters assist in DR election?
98 How to advertise a default-route if it doesn’t exist in the RIB?
99 What is OSPF’s metric? How is it identified in routing table? Does it support redistribution?
100 Explain LSA and its all Types such as LSA 1, 2, 3,4,5,7. When do we use LSA type 6?
101 What is the concept of “auto cost reference-bandwidth” and in what scenarios we should use it?
102 Why it’s known as Link state protocol? How it’s different than EIGRP? What algorithm does it use?
103 Explain Area Border Router?
104 What will happen if we make priority of an OSPF router as “zero”?
105 How do I change the reference bandwidth in OSPF?
106 How does OSPF calculate its’ metric or cost?
107 How Do We Configure OSPF Routing Protocol?
108 What are Different OSPF LSA Types?
109 What are the states used in OSPF when forming neighborship?
110 What Is Autonomous System Border Router?
111 What are different neighbor states in OSPF?
112 Which type of area blocks external route?
113 What algorithm is used by OSPF if equal cost routes exist?
114 What are the multicast IPs used by OSPF? What multicast IP does DR/BDR router and non-DR use?
115 What are the packet types does OSPF use? Explain Hello, Dead Timers, LSA, LSU, LSR packets.
116 What is role of topology and routing table in OSPF?
117 What Is OSPF Router-Id?
118 Does DR/BDR election happen in OSPF Point to Point Network?
119 What are the tables Maintained By OSPF?
120 What is the link-state retransmit interval, and what is the command to set it?
121 What different activities neighbour router perform in OSPF?
122 What is the purpose of the variable IP-OSPF-Transmit-Delay?
123 Is it true that only the static option of the virtual link in OSPF allows discontiguous networks, regardless of the mask propagation properties?
124 On which algorithms OSPF depends? What is the principle behind it?
125 Are the multicast IP addresses mapped to MAC-level multicast addresses?
126 Does the Cisco OSPF implementation support IP TOS-based routing?
127 What is the concept of Virtual-link in OSPF? Can virtual link be formed thru stub area?
128 Does the offset-list subcommand work for OSPF?
129 Can an OSPF default be originated into the system based on external information on a router that does not itself have a default?
130 Briefly explain functioning and working of different OSPF?
131 Can I use the distribute-list in/out command with OSPF to filter routes?
132 How can I give preference to OSPF interarea routes over intra-area routes?
133 What Is The Default Dead Interval?
134 What LSA is used for inter area communication? What LSA type is used for inter protocol communication in OSPF?
135 What are the different OSPF network types and give an example for each?
136 Do I need to manually set up adjacencies for routers on the Switched Multimegabit Data Service (SMDS) cloud with the OSPF neighbor subcommand?
137 Explain the concept of Area Border Router (ABR) and Autonomous System Border Router (ASBR). Can router sitting between area 2 and 3 be called as ABR?
138 How OSPF inter area, external routes are denoted or represented in routing table?
139 When routes are redistributed between OSPF processes, are all shortest path first algorithm (SPF) metrics preserved, or is the default metric value used?
140 Name tables which OSPF maintain? Question 48: What is the DR/BDR in OSPF? How these are elected and in what scenario?
141 How does Cisco accommodate OSPF routing on partial-mesh Frame Relay networks?
142 Which address-wild-mask pair should I use for assigning an unnumbered interface to an area?
143 What Is The Need For Dividing The Autonomous System Into Various Areas?
144 Can I have one numbered side and leave the other side unnumbered in OSPF?
145 Why do I receive the “cannot allocate router id” error message when I configure Router OSPF One?
146 What Is The Benefit Of Dividing The Entire Network Into Areas?
147 Why do I receive the “unknown routing protocol” error message when I configure Router OSPF One?
148 What Is The Default Hello Interval?
149 What do the states DR, BDR, and DROTHER mean in show ip OSPF interface command output?
150 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?
151 Why do I not see OSPF neighbors as FULL/DR or FULL/BDR on my serial link?
152 Do I need any special commands to run OSPF over BRI/PRI links?
153 Explain OSPF Timers?
154 Do I need any special commands to run OSPF over asynchronous links?
155 Which Cisco IOS Software release began support for per-interface authentication type in OSPF?
156 Can I control the P-bit when importing external routes into a not-so-stubby area (NSSA)?
157 Why are OSPF show commands responding so slowly?
158 What does the clear ip OSPF redistribution command do?
159 Does OSPF form adjacencies with neighbors that are not on the same subnet?
160 What Are The Steps Required To Change Neighborship Into Adjacency?
161 How often does OSPF send out link-state advertisements (LSAs)?
162 How do I stop individual interfaces from developing adjacencies in an OSPF network?
163 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?
164 Explain OSPF LSA, LSU And LSR?
165 What problems can cause OSPF neighborship in “down” state?
166 Where does the summarization happen in OSPF? Which command is used for summarization at ABR and at ASBR?
167 Should I use the same process number while configuring OSPF on multiple routers within the same network?
168 What is “Process-id”? Does it have local or global significance? Does it need to be same on OSPF neighbor routers?
169 How does OSPF use two Multilink paths to transfer packets?
170 Explain The Various OSPF States?
171 Can we have OSPF run over a GRE tunnel?
172 Is there a way to manipulate and prefer the Type 3 LSAs to originate from two different areas sent to the non-backbone area?
173 Is there a drop/flap of an OSPF neighborship when changing an OSPF area type from NSSA no-summary to NSSA?
174 Why DR And BDR Are Elected In OSPF?
175 What is the concept of “Area” in OSPF? What is Backbone area, stub area, Totally Stubby Area, Not So Stubby area (NSSA)?
176 In the %OSPF-5-ADJCHG: Process ID, Nbr [ip-address] on Port-channel31 from FULL to EXSTART, SeqNumberMismatch error message, what does SeqNumberMismatch signify?
177 Is there a way to compare Cisco NX-OS/IOS OSPF commands?
178 Is there any feature of OSPF protocol for quick convergence and a slow re-convergence of routes?
179 What does BADSEQNUM in the %OSPF-5-NBRSTATE: OSPF-101 [5330] Process 101, Nbr 10.253.5.108 on Vlan7 02 from FULL to EXSTART, BADSEQNUM OSPF log message mean?
180 What will be Hello/Dead timers in network having link capacity of >T1 and <=T1?
181 What Parameters Must Match For Two Routers To Become Neighbors?
182 What is O E1, O E2 letters in OSPF? Which is default external type 1 or external type 2?
