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Scenario-based practice

OSPF Troubleshooting Scenarios

Practise 350-501 Cisco SPCOR / CCNP Service Provider Core 350-501 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
350-501
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 network engineer is troubleshooting OSPFv3 on a service provider's IPv6 network. The router shows that OSPFv3 adjacency never reaches FULL, says 'Init'. The neighbor is directly connected over a point-to-point link. What is the most likely cause?

Question 2mediummultiple choice
Review the full OSPF breakdown →

During an MPLS network migration from LDP to Segment Routing, an engineer notices that some routers are not advertising Prefix-SIDs for certain loopbacks. The IGP is OSPF. What configuration is required on these routers to advertise Prefix-SIDs?

Question 3mediummultiple choice
Review the full OSPF breakdown →

A service provider is deploying MPLS L3VPN and notices that BGP next-hop resolution for VPNv4 routes fails on the PE routers. The PE routers are running OSPF as the IGP and have loopback interfaces used for LDP and BGP peering. Which configuration change should the engineer implement to ensure that the BGP next-hop is reachable?

Question 4mediummultiple choice
Review the full OSPF breakdown →

A service provider is deploying MPLS L3VPN over an OSPF backbone. The PE routers are configured with OSPF as the IGP. The CE router of customer A is connected to two PEs for redundancy. Which configuration is required on the PE routers to ensure that the CE router can load-balance traffic across both PEs without loops?

Question 5mediummulti select
Review the full OSPF breakdown →

Which TWO statements correctly describe the use of OSPF in a service provider network?

Question 6mediummultiple choice
Review the full OSPF breakdown →

An engineer is troubleshooting an MPLS L3VPN where customers behind CE1 cannot reach a specific prefix behind CE2. The PE routers are using OSPF as the IGP and LDP for label distribution. On PE2, the prefix is present in the VRF routing table, but not in the VRF forwarding table. What is the most likely cause?

Question 7mediummultiple choice
Review the full OSPF breakdown →

Refer to the exhibit. The router cannot form a full OSPF adjacency with 10.0.0.2. Which is the most likely cause?

Exhibit

show ip ospf neighbor
Neighbor ID     Pri   State           Dead Time   Address         Interface
10.0.0.2        1    EXSTART/DR     00:00:35    10.0.1.2        GigabitEthernet0/0
Question 8mediummultiple choice
Review the full OSPF breakdown →

A service provider is running OSPF in their core network. After a link failure, routing convergence is taking longer than expected. The engineer suspects the issue is related to the SPF calculation. Which OSPF feature can reduce the SPF calculation time?

Question 9easymultiple choice
Review the full OSPF breakdown →

Based on the exhibit, which OSPF network type is configured on this interface?

Exhibit

Refer to the exhibit.

Router# show ip ospf interface GigabitEthernet0/0
 GigabitEthernet0/0 is up, line protocol is up
   Internet Address 10.10.10.1/24, Area 0
   Process ID 1, Router ID 192.168.1.1
   Network Type POINT_TO_POINT, Cost: 10
   Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
     oob-resync timeout 40
   Adjacency State FULL
Question 10easymultiple choice
Review the full OSPF breakdown →

A network engineer is configuring MPLS LDP on a new router. After enabling LDP globally and on the interface, the LDP session does not establish. The IGP (OSPF) is fully operational. What should the engineer verify first?

Question 11mediumdrag order
Review the full OSPF breakdown →

Drag and drop the steps to configure OSPF on a Cisco IOS router into the correct order.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps
Order
1Step 1
2Step 2
3Step 3
4Step 4
5Step 5
Question 12mediummultiple choice
Review the full OSPF breakdown →

An OSPF network uses point-to-point links. The engineer notices that LSAs are being flooded every 30 minutes even when no topology changes occur. What is the most likely reason?

Question 13hardmultiple choice
Review the full OSPF breakdown →

Refer to the exhibit. An engineer configures MPLS LDP on a router. The router has two interfaces with IP addresses 10.0.0.1/30 and 10.0.0.5/30. The engineer notices that LDP sessions are not established. The OSPF neighbor adjacencies are up. What is the most likely cause?

Exhibit

Refer to the exhibit.

interface GigabitEthernet0/0
 ip address 10.0.0.1 255.255.255.252
 mpls ip
 mpls mtu 1500
!
interface GigabitEthernet0/1
 ip address 10.0.0.5 255.255.255.252
 mpls ip
 mpls mtu 1500
!
router ospf 1
 network 10.0.0.0 0.0.0.3 area 0
 network 10.0.0.4 0.0.0.3 area 0
!
mpls ldp router-id Loopback0 force
!
mpls label range 100 199
!
mpls label protocol ldp
Question 14easymultiple choice
Review the full OSPF breakdown →

A network engineer is troubleshooting an OSPF issue in a service provider network. The network uses OSPFv2 with multiple areas. Routers in area 0 are able to ping each other, but routers in area 1 cannot reach routers in area 2. All routers are OSPF-enabled and have correct network type configurations. What is the most likely cause?

Question 15hardmultiple choice
Review the full OSPF breakdown →

A service provider is deploying an MPLS L3VPN solution for a customer with two sites. The PE routers are running OSPF as the IGP and LDP for label distribution. The provider wants to ensure that customer traffic is load-balanced across two equal-cost paths between the PEs. The network team notices that all traffic is taking only one path despite the IGP showing equal-cost routes. The team has verified that the MPLS forwarding table on the P router shows only one label entry for the BGP next-hop. The team suspects a load-balancing issue. Which action best resolves the problem?

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