Cisco Certified Network Associate (CCNA) 200-301 Practice Test 43
Question 420
A branch routing engineer is validating a repair. Earlier, r1 uses Hello 10/Dead 40 and R2 Hello 5/Dead 20; hellos arrive but the adjacency never reaches FULL. Which postchange check most directly establishes the specific problem is resolved?
- One end remains 10/40 and the other 5/20 but both ratios are one-to-four.
- A local OSPF router ID appears but the neighbor remains Down or Init due to timer mismatch.
- Physical interface counters rise while authenticated OSPF hellos still disagree on timers.
- Both ends now show identical Hello/Dead timers and the expected neighbor reaches the appropriate Full state; inspect `show ip ospf interface` and neighbor output.
Explanation
Correct Answer
D:The earlier peers used 10/40 and 5/20 intervals. Aligning real interval values, not their ratios, permits compliant hello exchange and adjacency formation.
Incorrect Answers
A:OSPF requires actual timer values to match, not merely proportional intervals.
B:A router ID does not establish working neighbor compatibility.
C:Ethernet link traffic is not proof of Full OSPF adjacency.
Question 421
Two routers on a directly connected point-to-point link previously failed to become OSPF neighbors because R1 used area 0 and R2 used area 1. Both now have area 0 configured. What verification most completely proves that the area mismatch was removed and adjacency recovered?
- Inspect show ip ospf interface on R1 alone to see its local Area 0 field without checking R2 or adjacency
- Verify both router IDs are nonzero without checking the transit interfaces or neighbor state
- Confirm the transit-interface Area 0 setting on BOTH routers and a FULL neighbor state on the intended link
- Compare hello/dead timers on only R1 and assume equal timers imply compatible areas
Explanation
Correct Answer
C:The correction addresses the area field on both ends, so first inspect the transit interfaces on R1 and R2 with show ip ospf interface and confirm that the shared network belongs to area 0 on each device. Then use show ip ospf neighbor to verify the intended peer reaches FULL on the point-to-point link. These observations cover the configuration cause and the operational result. Merely inspecting one router, its router ID, or its timers cannot prove this specific mismatch was fully resolved; an established neighbor relationship demonstrates that OSPF exchange progressed past the earlier area rejection.
Incorrect Answers
A:Seeing Area 0 on R1 only does not prove R2 uses the same area. OSPF neighbors must agree on the area for their common link, and the original failure was specifically caused by an area mismatch between the two devices. A local configuration observation also does not prove that database exchange completed. This option checks only one required component and leaves both the opposite interface and the actual adjacency unverified.
B:Valid OSPF router IDs uniquely identify participating routers, but router ID values do not encode the area assignment of the transit interfaces. Two routers can have valid IDs and still reject hello exchanges because they are in different areas. Router IDs are useful when identifying peers, but the acceptance test must separately establish that both interfaces now use matching area settings and that a working adjacency has formed.
D:Hello and dead timers must be compatible for normal OSPF adjacency on a link, but they are a separate parameter from the area identifier. Matching the timer values on one router provides no evidence that the second router uses area 0; even matching timers on both routers would not by itself establish FULL adjacency. The original problem was an area mismatch, so a timer-only check is inadequate despite being relevant in another kind of neighbor failure.
Question 422
A branch routing engineer has repaired a network problem. R1 has 192.0.2.1/24 and R2 has 192.0.2.2/25; network/mask validation fails while the switch is forwarding frames. Which device or protocol check is the strongest evidence that this particular failure is gone?
- Both router transit interfaces now share a compatible IPv4 subnet and mask, and `show ip ospf neighbor` shows a healthy adjacency on that broadcast link.
- The routers can ping their overlapping IPs but OSPF Hello network-mask fields remain /24 and /25.
- Change only OSPF cost while leaving the /24 versus /25 netmask mismatch intact.
- `show interfaces` says both links have carrier but OSPF neighbor state remains Down.
Explanation
Correct Answer
A:R1 /24 versus R2 /25 created inconsistent OSPF broadcast netmask fields. Correct both address/mask settings and confirm protocol neighbor establishment, not only ping.
Incorrect Answers
B:Some IP reachability can coexist with OSPF mask-validation failure.
C:Path cost does not fix broadcast-subnet hello compatibility.
D:Layer 1/2 connectivity does not prove correct OSPF packet acceptance.
Question 423
A network acceptance test follows this reported failure: Hello packets arrive, but packet authentication fails because one router uses a different digest key from its peer. Which verification most specifically demonstrates the repaired function rather than checking an unrelated feature?
- Both peers have matching authentication type/key and an accepted authenticated OSPF adjacency reaches Full without digest validation errors.
- Hellos still generate key-mismatch authentication errors, but the physical link LED is green.
- The two router IDs are unique yet the configured OSPF keys continue to differ.
- An unrelated route to a loopback exists, but the affected authenticated neighbor never establishes Full.
Explanation
Correct Answer
A:The earlier hello packets arrived but failed authentication. A healthy cryptographic neighbor exchange with no authentication failures is the specific repair proof.
Incorrect Answers
B:Ethernet carrier does not bypass failed OSPF packet authentication.
C:Unique identities do not replace matching authentication settings.
D:A separate route cannot prove this adjacency accepts signed hellos.
Question 424
A branch routing engineer is validating a repair. Earlier, an uplink accidentally marked passive suppresses OSPF hellos to its actual router neighbor and the O route disappears. Which postchange check most directly establishes the specific problem is resolved?
- The uplink remains passive and `show ip ospf neighbor` lists no peer, but the user LAN remains advertised.
- Only a route 0/0 exists while the previously learned OSPF destination remains absent.
- The actual router-to-router uplink is removed from `passive-interface`, establishes its OSPF neighbor, and the expected learned O route returns to the RIB.
- A CDP neighbor is visible on the link but OSPF remains passive.
Explanation
Correct Answer
C:Passive suppresses OSPF hello exchange. Reenabling hellos on the transit and confirming the specific learned remote prefix tests both neighbor control and route installation.
Incorrect Answers
A:A passive LAN advertisement does not repair the required router-to-router adjacency.
B:A default route is not proof of recovery of the targeted OSPF path.
D:CDP physical neighbor discovery does not create OSPF hello adjacency.
Question 425
R1 and R2 share a routed Ethernet link that administrators intentionally configured with OSPF network type point-to-point, so no designated-router election should occur on that link. Which command output most directly proves the intended interface network type is active?
- show ip ospf neighbor lists the remote router in FULL state, with no interface network-type field
- show ip ospf interface GigabitEthernet0/1 displays Network Type POINT_TO_POINT and State POINT_TO_POINT
- show ip route contains an OSPF-learned route to a remote subnet
- show ip ospf database contains link-state advertisements but no displayed interface type
Explanation
Correct Answer
B:The show ip ospf interface command reports the OSPF network type and interface state used on the selected link. Seeing Network Type POINT_TO_POINT and State POINT_TO_POINT on GigabitEthernet0/1 directly establishes the configured OSPF link behavior. A point-to-point OSPF network does not elect a DR and BDR; eligible neighbors ordinarily form a direct full adjacency subject to matching area, timers, authentication and link reachability. By checking the explicit interface type, the operator verifies the intended behavior rather than inferring it from a route learned elsewhere or a neighbor state that could also exist on a broadcast network.
Incorrect Answers
A:An OSPF neighbor can reach FULL on a point-to-point link, but neighbors can also be FULL on other network types when their adjacency conditions are satisfied. The neighbor listing alone does not state the configured OSPF interface network type. This test must prove the interface is POINT_TO_POINT and therefore uses point-to-point adjacency behavior rather than a broadcast DR/BDR election. The command needs to expose that network-type field directly.
C:An OSPF route in the routing table proves a path was installed from OSPF information, not which OSPF network type was active on this particular Ethernet interface. The route might have been learned across a different interface or already be retained through another adjacency. It cannot show whether the monitored link uses point-to-point behavior instead of broadcast DR and BDR election. Inspect the interface-specific OSPF state directly.
D:The link-state database describes LSAs used in SPF route computation, but a general database display does not directly expose the network-type configuration of GigabitEthernet0/1. The user needs evidence that the particular link is running point-to-point OSPF operation. A database that is populated does not distinguish the link from an otherwise working broadcast segment, so relying on it would not settle the requested verification.
Question 426
Three OSPFv2 routers share an Ethernet broadcast segment in area 0. After priorities were configured and the DR election converged, the engineer needs to identify each neighbor’s current DR or BDR role. Which IOS output is most direct?
- show ip interface brief, showing interface addresses and line status
- show ip ospf neighbor, showing neighbor states such as FULL/DR and FULL/BDR
- show ip route ospf, showing prefixes learned from OSPF
- show spanning-tree vlan 10, showing the Ethernet STP root and ports
Explanation
Correct Answer
B:On a broadcast OSPF network, neighbor relationships include election-specific states that indicate which routers are designated or backup designated routers. The show ip ospf neighbor output displays neighbor identifiers and states such as FULL/DR, FULL/BDR, or 2WAY/DROTHER, making it the direct place to inspect an adjacent router’s elected role. Router priority affects a DR/BDR election but an already elected DR is not automatically preempted simply because a neighbor’s priority increased later. Verify the current neighbor state after convergence, and use show ip ospf interface if you also need to inspect the local interface’s own DR/BDR information and configured priority.
Incorrect Answers
A:The show ip interface brief command lists IP addressing and line-protocol status. It can confirm the participating link is up, but it does not show OSPF neighbors or identify which neighbor was elected DR or BDR on a broadcast segment. The OSPF adjacency can fail even when the interface shows up/up, so Layer 3 interface health alone is not the requested election evidence.
C:The show ip route ospf command displays routes that were installed using OSPF. Those routes can be present even when the particular Ethernet segment’s DR/BDR election differs from expectations. The routing table does not identify the current DR or BDR role of each neighbor. To answer an election question, inspect OSPF neighbor and interface operational state rather than inferred data-plane reachability.
D:The show spanning-tree vlan command belongs to Ethernet spanning-tree topology, where switches elect an STP root bridge and assign port roles. OSPF’s designated-router election is a Layer 3 adjacency mechanism and is separate from STP root selection. A switch may be the root bridge without any relation to which IP router becomes DR. STP output therefore cannot establish OSPF DR/BDR neighbor states.
Question 427
A network acceptance test follows this reported failure: One healthy router remains DROTHER and never wins DR election because its interface priority is zero. Which verification most specifically demonstrates the repaired function rather than checking an unrelated feature?
- Declare failure solely because the priority-zero router never becomes DR, despite functional DR adjacency.
- Raise priority to 255 to preserve DROTHER status and guarantee it will never be elected.
- `show ip ospf interface` reports interface priority 0 and DROTHER, with healthy Full adjacency to the elected DR/BDR where appropriate.
- Remove OSPF from the interface so no DR/BDR role displays, then call that healthy adjacency.
Explanation
Correct Answer
C:A priority-zero router should remain ineligible for the DR role, not be forced to become DR. Accept the intended non-designated role while checking route exchange works.
Incorrect Answers
A:Ineligibility is the purpose of priority zero.
B:A high nonzero priority increases DR election eligibility rather than preventing it.
D:No OSPF participation would defeat neighbor and route exchange.
Question 428
A branch routing engineer is validating a repair. Earlier, two DROTHERs show 2-WAY but route exchange through the DR works; someone incorrectly treats the stable state as failure. Which postchange check most directly establishes the specific problem is resolved?
- Demand every DROTHER pair reach Full even when all routes are functioning through the DR.
- Interpret 2-WAY as no reciprocal Hello reception, ignoring that 2-WAY explicitly indicates bidirectional neighbor discovery.
- `show ip ospf neighbor` displays Full with DR/BDR and 2-WAY between the DROTHER pair, while expected OSPF routes are exchanged.
- Disable the DR to remove the 2-WAY listing and ignore loss of route exchange.
Explanation
Correct Answer
C:Broadcast OSPF uses DR/BDR to reduce full adjacencies. Two DROTHER neighbors need not become Full directly when there is a healthy designated router exchanging the LSDB.
Incorrect Answers
A:That is not the usual broadcast multiaccess adjacency model.
B:2-WAY can be stable between DROTHER peers.
D:Removing the designated router is not a valid functional acceptance test.
Question 429
Before remediation, R1 uses the default OSPF reference bandwidth of 100 Mbps, so its 1-Gbps and 10-Gbps links both have automatic cost 1. An engineer updates a consistent reference-bandwidth policy on the routers to distinguish faster links. Which postchange observation best proves that the intended OSPF preference is working?
- Only `show running-config` shows a changed reference-bandwidth command, but both interfaces still display cost 1 and routes remain tied.
- A single ping to the destination succeeds but the OSPF interface costs and chosen next hop were not inspected.
- `show ip ospf interface` shows cost 10 on the 1-Gbps link and cost 1 on the 10-Gbps link (with 10000-Mbps reference), and `show ip route`/the FIB reflect the intended lower-total-cost path.
- The router hostname is different, but the measured OSPF costs and installed equal-cost next hops remain unchanged.
Explanation
Correct Answer
C:With a 10000-Mbps reference bandwidth, typical default IOS OSPF cost is approximately 10000/1000=10 for 1 Gbps and 10000/10000=1 for 10 Gbps. Confirm those per-interface costs, a consistently applied reference policy and the resulting lower-cost route or FIB next hop for the intended prefix. This checks the mechanism that was broken, rather than merely confirming syntax or basic packet reachability.
Incorrect Answers
A:A configuration line alone does not prove the effective interface cost or forwarding choice. If both 1-Gbps and 10-Gbps links still have cost 1, the initial cost tie remains and no demonstrated path preference improvement has occurred.
B:Successful reachability does not demonstrate whether OSPF now distinguishes the link speeds or still uses equal-cost forwarding. Verification must inspect effective interface costs and the selected destination route, not just ICMP success.
D:Hostnames are not a factor in OSPF SPF path-cost calculation. If the installed equal-cost paths and interface costs have not changed, a rename does not address the original misleading metric tie.
Question 430
A branch routing engineer is evaluating a deployment. Two routers on one host VLAN should present one stable virtual default-gateway IP and MAC that survives active-router failure. What approach correctly addresses the stated requirement?
- Configure every host with R1’s physical interface IP and assume R2 takeover changes that address automatically.
- Assign separate default gateways from R1 and R2 at random and assume all clients will choose the surviving one.
- Configure a common FHRP virtual IP on the host subnet and use it as every client’s default gateway; the active owner answers for the virtual MAC.
- Use a shared DNS server name as the FHRP MAC address instead of a virtual gateway IP.
Explanation
Correct Answer
C:HSRP/VRRP provide a stable host-facing virtual next hop while router roles change. On failure, the surviving eligible router takes ownership of the virtual IP/MAC without reconfiguring clients.
Incorrect Answers
A:An FHRP transition moves the virtual gateway, not R1’s unique physical interface IP.
B:Hosts using a failed physical gateway may not switch without explicit alternate-gateway logic.
D:Default-gateway forwarding uses an IP next hop and resolved L2 MAC, not a DNS hostname masquerading as a MAC.
