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OSPF Troubleshooting Scenarios

Practise 300-410 Cisco CCNP ENARSI 300-410 OSPF questions covering neighbour states, router IDs, areas, timers, passive interfaces, OSPF cost, route selection, and command-output troubleshooting.

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15
scenario questions
300-410
exam code
Cisco
vendor

Scenario guide

How to approach ospf troubleshooting scenarios

OSPF neighbour adjacencies, route advertisements, and DR/BDR elections appear consistently on the CCNA. These questions test whether you can read OSPF state from show commands and identify why two routers fail to reach FULL adjacency or why a route isn't being learned.

Quick answer

OSPF questions usually test neighbour formation, areas, router IDs, route preference, metrics and command-output interpretation.

How OSPF neighbours form and why adjacency can fail.

How router ID, area ID, timers, passive interfaces and authentication affect OSPF.

How OSPF cost influences route selection.

How to read show ip route and show ip ospf neighbor output.

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Practice set

Practice scenarios

Question 1hardmultiple choice
Review the full OSPF breakdown →

A large enterprise network uses OSPFv3 for IPv6 routing. Router R1 and R2 are connected via a multi-access Ethernet link. R1 is configured with 'ipv6 ospf network point-to-point' while R2 uses the default broadcast network type. R1 has an IPv6 ACL applied inbound on its interface that permits only OSPF (89) and denies all other traffic. R2 is unable to form a full OSPF adjacency with R1. R2 shows 'OSPFv3 adjacency state is EXSTART/EXCHANGE' and logs 'Bad LSReq'. What is the root cause?

Question 2hardmultiple choice
Review the full OSPF breakdown →

An enterprise uses VRF-lite with IPv6. VRF A on R1 leaks routes to VRF B using route-target import/export. R1 has an IPv6 ACL applied inbound on the interface in VRF A that permits only OSPFv3 and denies all other traffic. R1's VRF B has a static default route pointing to a next-hop in VRF A. Traffic from VRF B to the internet fails. R1 shows 'ping vrf B 2001:db8:2::1' fails, but 'ping vrf A 2001:db8:2::1' succeeds. What is the root cause?

Question 3hardmultiple choice
Review the full OSPF breakdown →

An OSPFv3 network has multiple areas. Area 0 includes R1 and R2. Area 1 includes R2 and R3. R2 is an ABR. R1 has an IPv6 ACL applied inbound on the interface to R2 that permits only OSPFv3 and denies all other traffic. R3 advertises a prefix 2001:db8:3::/48 into Area 1. R1's routing table shows the prefix but with a next-hop of R2. R1's uRPF is configured in strict mode on the interface to R2. Traffic from R1 to 2001:db8:3::1 is dropped. R1 shows 'show ipv6 cef 2001:db8:3::/48' points to R2's link-local address. What is the root cause?

Question 4easymultiple choice
Review the full OSPF breakdown →

What is the default hello interval for OSPFv3 on a broadcast network type in Cisco IOS-XE?

Question 5hardmultiple choice
Review the full OSPF breakdown →

What is the default metric for an IPv6 static route redistributed into OSPFv3?

Question 6hardmultiple choice
Review the full OSPF breakdown →

What is the default dead interval multiplier for OSPFv3?

Question 7easymultiple choice
Review the full OSPF breakdown →

What is the default administrative distance for OSPFv3 internal routes?

Question 8hardmultiple choice
Review the full OSPF breakdown →

An engineer configures IPv6 uRPF strict mode on an interface of a router that participates in OSPFv3. The router starts dropping OSPFv3 Hello packets received on that interface, causing the OSPFv3 neighbor adjacency to fail. Which is the most likely explanation?

Question 9hardmultiple choice
Review the full OSPF breakdown →

An engineer configures an IPv6 ACL to filter OSPFv3 traffic on a router interface. The ACL includes a deny entry for OSPFv3 (protocol 89) followed by a permit ipv6 any any. However, OSPFv3 adjacencies still fail to form over that interface. Which is the most likely explanation?

Question 10hardmultiple choice
Review the full OSPF breakdown →

An engineer configures IPv6 uRPF strict mode on an interface that is used for both IPv6 traffic and OSPFv3 routing. The router is an ABR with multiple areas. OSPFv3 adjacencies form correctly, but some IPv6 data traffic is dropped. The show ipv6 interface command shows uRPF is enabled. Which is the most likely explanation?

Question 11mediummultiple choice
Review the full OSPF breakdown →

An engineer applies a CoPP policy to a router to protect the control plane. The policy includes a class-map that matches all ICMP traffic and polices it to 5000 bps. After the policy is applied, the engineer notices that OSPF adjacencies are going down. The OSPF hello packets are not being received. What is the most likely cause?

Question 12easymultiple choice
Review the full OSPF breakdown →

A network engineer runs the following command on Router R1:

R1# show policy-map control-plane

Control Plane

Service-policy input: CoPP-IN

Class-map: CoPP-OSPF (match-all) 1000 packets, 60000 bytes 5 minute offered rate 2000 bps, drop rate 0000 bps Match: access-group 140 police: cir 64000 bps, bc 12000 bytes, be 12000 bytes conformed 1000 packets, 60000 bytes; actions: transmit exceeded 0 packets, 0 bytes; actions: drop violated 0 packets, 0 bytes; actions: drop

Based on this output, which statement is correct?

Question 13mediummultiple choice
Review the full OSPF breakdown →

Consider the following CoPP configuration:

class-map match-any COPP-ROUTING match protocol ospf match protocol eigrp match protocol bgp ! policy-map COPP-POLICY

class COPP-ROUTING

police 32000 conform-action transmit exceed-action drop

class class-default

police 64000 conform-action transmit exceed-action drop ! control-plane service-policy input COPP-POLICY

What is a potential issue with this configuration?

Question 14mediummultiple choice
Review the full OSPF breakdown →

Analyze the following partial configuration:

access-list 101 permit tcp any any eq 179
access-list 
101 permit udp any any eq 646
access-list 
101 permit ospf any any

! class-map match-all COPP-BGP match access-group 101 ! policy-map COPP-POLICY

class COPP-BGP

police 48000 conform-action transmit exceed-action drop

class class-default

police 128000 conform-action transmit exceed-action drop !

interface GigabitEthernet0/0
 ip address 192.168.1.1 255.255.255.0

! control-plane service-policy input COPP-POLICY

Which statement is true?

Question 15mediummultiple choice
Review the full OSPF breakdown →

A network engineer runs the following command to troubleshoot a Control Plane Policing (CoPP) issue:

R1# debug ip ospf adj

OSPF adjacency debugging is on R1#

*Mar  1 00:05:23.123: OSPF: Rcv pkt from 10.1.1.2, FastEthernet0/0, area 0.0.0.0, packet type: 1 (Hello)
*Mar  1 00:05:23.123: OSPF: 2 Way Communication to 10.1.1.2 on FastEthernet0/0, state 2WAY
*Mar  1 00:05:23.124: OSPF: Send immediate hello to nbr 10.1.1.2, src address 10.1.1.1, on FastEthernet0/0
*Mar  1 00:05:23.124: OSPF: Rcv pkt from 10.1.1.2, FastEthernet0/0, area 0.0.0.0, packet type: 2 (DBD)
*Mar  1 00:05:23.125: OSPF: Rcv DBD from 10.1.1.2, seq 0x1234, opts 0x2, flag 0x7, mtu 1500 state EXSTART
*Mar  1 00:05:23.126: OSPF: Nbr 10.1.1.2 has state FULL

What does this output indicate?

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