CCNA OSPF Questions

Displays VLAN port membership; irrelevant to OSPF verification.

Shows STP topology; does not provide OSPF neighbor status.

Displays the switch's MAC address table; no OSPF information.

This is incorrect because OSPF operates normally on /30 subnets commonly used for point-to-point links. Subnet mask size does not prevent OSPF adjacency.

This is incorrect because OSPF process IDs are locally significant identifiers and do not need to match between routers to form neighbors.

This is incorrect because OSPF runs over routed interfaces and does not require interfaces to be configured as switch trunks, which are used for VLAN tagging.

A larger wildcard mask does not override the passive-interface setting; adjacency still fails.

Adjacency depends on area and authentication, not on the router-local process ID; passive-interface is the real issue.

The root cause is a configuration that blocks hellos, not a transient state; the reset is ineffective.

'ipv6 router ospf <process-id>' is a global configuration command, not an interface command; enabling OSPFv3 on an interface requires the 'ipv6 ospf <process-id> area <area-id>' command.

'show ipv6 ospf neighbor' displays OSPFv3 neighbor adjacencies, not the link-state database; to view the LSDB, use 'show ipv6 ospf database'.

The type of routing protocol (link-state vs. distance vector) does not determine route preference when comparing routes from different protocols. Route selection is based on administrative distance, not protocol characteristics.

Metrics are only comparable within the same routing protocol. Different protocols use different metrics (e.g., OSPF uses cost, EIGRP uses composite metric), so they cannot be directly compared. Administrative distance is used to choose between protocols.

By default, a router installs only the best route (lowest AD) for a given prefix into the routing table. Both routes are not installed unless features like equal-cost multipath or policy routing are configured, which is not the case here.

Incorrect because OSPF process IDs are locally significant and do not need to match between routers for adjacency or route exchange.

Incorrect because both routers' interfaces are in the same subnet 10.20.12.0/24, so subnet mismatch is not the cause of missing routes.

Incorrect because OSPF supports multiple link types including Ethernet; it is not limited to serial links only.

The OSPF /24 route is less specific than the static /25 route. The longest prefix match rule dictates that the /25 route is preferred for destination 203.0.113.10, which falls within the /25 range.

Equal-cost load balancing only applies when multiple routes have the same prefix length and metric. Here, the prefix lengths differ (/24 vs /25), so the longest prefix match selects the /25 route exclusively.

Overlapping routes are common in routing tables and do not cause a problem. The router always selects the most specific match (longest prefix) for forwarding, so both routes can coexist.

This reflects a common misunderstanding that AD is the sole tie-breaker between routes from different sources, ignoring prefix length priority.

Candidates might assume that if the OSPF route is not used, it must be inactive; however, the exhibit does not show this.

Candidates may mistake metric for the primary selection criterion, not realizing prefix length dominates all other route comparison steps.

Candidates often recall that duplicate router IDs break adjacencies and assume any flapping must be caused by this. They miss the regular timing correlation with the dead interval.

Network type mismatch is a common OSPF troubleshooting topic, and candidates may attribute any flapping to mismatched types, overlooking the precise timer-derived timing.

Authentication problems are a frequent first guess for adjacency failures. The flapping behavior here contradicts a permanent rejection.

Option B is incorrect because OSPF does not compare its metric directly against EIGRP metrics. Metrics are protocol-specific and only administrative distance is used to compare routes across different protocols.

Option D is incorrect because OSPF process IDs are locally significant and do not need to match between neighboring routers. Adjacency forms based on matching parameters like area ID and authentication, not process ID.

Option E is incorrect because OSPF supports equal-cost multipath (ECMP) routing, allowing multiple routes with the same cost to be installed and used simultaneously for load balancing.

Candidates mistakenly think any non-FULL state implies a timer mismatch, overlooking that timer issues prevent even reaching 2WAY.

Some candidates assume any DR/BDR-related issue indicates a network type mismatch, but the exhibit clearly shows successful DR/BDR formation, ruling out this option.

Candidates may confuse LSA reachability with neighbor adjacency requirements. The 2WAY state proves basic connectivity is intact.

Believing that a static route is removed from the routing table when a better route exists, rather than understanding it remains but is inactive.

Assuming that a static route's next-hop must be directly attached, ignoring that recursive routing via another routing protocol or static route is allowed.

Thinking that recursive static routes are prone to loop suppression, rather than understanding that the route is simply withdrawn when the next-hop is no longer reachable.

Using 'ip ospf cost 65535' on the LAN interface only changes the OSPF metric for that interface. It does not prevent the router from sending or receiving OSPF Hello packets, so neighbor adjacencies can still form, which is not the desired behavior.

Disabling OSPF globally and redistributing connected routes is an overly complex and unnecessary approach. It does not selectively stop Hello packets on the LAN interface and can introduce routing complexity and instability.

Converting the LAN interface to a loopback interface changes the interface type entirely and is not a standard or practical solution for suppressing OSPF Hellos on a LAN. Loopbacks are logical interfaces used for router IDs and testing, not for controlling OSPF Hello behavior.

Point-to-point links connect only two routers directly and do not require or perform DR/BDR elections because there is no need to reduce flooding on a single link. Selecting this option is incorrect for Ethernet interfaces that default to broadcast.

Point-to-multipoint nonbroadcast network type requires manual neighbor configuration and does not perform DR/BDR elections by default. This does not match the default behavior of Ethernet interfaces.

Loopback interfaces are virtual interfaces used for router identification and do not participate in OSPF DR/BDR elections because they are not multiaccess networks.

This option is incorrect because a directly connected route, even though it has a lower administrative distance, does not override a more specific OSPF route due to prefix length precedence.

This option is incorrect because routers do not use multiple routes equally when one route is a more specific match; only the best matching route is used for forwarding.

This option is incorrect because routers can compare and select routes from different sources; differing sources do not prevent route usage if one route is the best match.

The specific factual error is that OSPF is a dynamic routing protocol that must be enabled on both ends of a link for adjacency to form; one-sided configuration does not work.

The specific factual error is confusing subnet masks with wildcard masks; OSPF uses inverse masks in network statements.

The specific factual error is using a host wildcard mask that does not cover the actual interface IPs; the correct wildcard mask must include the range of IPs on the link.

This option is incorrect because OSPF neighbor relationships do not depend on matching hostnames. Hostnames are administrative identifiers and do not affect OSPF protocol operations or LSA exchanges.

This option is incorrect because a /30 subnet is a standard subnet size for point-to-point links and does not prevent OSPF from operating or forming adjacencies. OSPF works normally over /30 subnets.

This option is incorrect because OSPF runs over routed interfaces and does not require interfaces to be configured as switch trunks. Trunking is related to VLAN tagging and switching, not OSPF adjacency.

The next-hop should be R3 (10.0.0.6), not R2 (10.0.0.2).

The AD must be higher than OSPF's 110 (e.g., 150) to act as a floating static route.

The destination network should be 203.0.113.0/24, not a default route.

Authentication mismatches prevent OSPF neighbors from reaching the 2-Way state by blocking bidirectional communication. Since the neighbors here have reached 2-Way, authentication mismatch is unlikely the cause.

Configuring the network type as point-to-point is not required on Ethernet segments and would change the adjacency formation behavior rather than explain the current normal 2-Way state with DROTHER routers.

Duplicate router IDs cause adjacency failures and routing problems but do not cause neighbors to remain in the 2-Way state with DROTHER routers. The output does not indicate a router ID conflict.

The static default route has an administrative distance of 200, which is higher than OSPF's default distance of 110. Therefore, OSPF's route is preferred, and the static route does not override it. Manual configuration does not bypass administrative distance; the router always prefers the lower distance.

Load balancing requires multiple routes with equal administrative distance and metric. Here, OSPF and the static route have different administrative distances (110 vs. 200), so they are not equal. The router will only use the best route (OSPF) and not load-balance.

Overlapping default routes are common and do not cause the router to ignore them. The router uses the route with the lowest administrative distance (OSPF) and ignores the static route unless OSPF fails. There is no conflict that would cause both to be ignored.

This option is incorrect because it assumes the router compares OSPF and EIGRP metrics directly. Metrics from different protocols are not comparable until administrative distance is considered, so the lower OSPF metric does not guarantee route installation.

This option is incorrect because load balancing occurs only when multiple equal-cost routes exist within the same routing protocol. Routes from different protocols are not automatically load-balanced simply because they reach the same destination.

This option is incorrect because the router automatically selects the best route using its decision process based on administrative distance and metric. Manual intervention is not required for route installation in this scenario.

The OSPF /16 route is less specific than the static /24 route. Although OSPF is a dynamic routing protocol, the router prefers the route with the longer prefix length, so this option is incorrect.

The default route is only used when no specific matching route exists. Since both OSPF and static routes cover the destination, the default route is not used here, so this option is incorrect.

Overlapping prefixes are normal in routing tables and do not prevent route selection. The router resolves overlaps using longest-prefix match, so this option is incorrect.

The router-ID is derived from the highest IP address on a loopback or physical interface, never from a MAC address.

A router-id change does not take effect immediately; you must clear the OSPF process or reload the router.

Router-IDs must be unique per router, not identical across all routers in the area.

The router does not discard the OSPF route; it installs both /16 and /24 entries because they represent different network-specific entries.

The traffic matches the /24 route, not the /16, so it would be forwarded via the EIGRP next-hop.

The /24 is a subset; traffic outside 172.16.10.0/24 matches only the /16 OSPF route.

This option is incorrect because OSPF process IDs are locally significant and do not need to match between routers. Different process IDs do not prevent adjacency formation.

This option is incorrect because the interfaces are in the same IPv4 subnet (10.1.50.0/24), which is a prerequisite for OSPF adjacency on broadcast networks.

This option is incorrect because OSPF commonly runs on Ethernet interfaces. Ethernet is a supported media type for OSPF neighbor discovery and adjacency formation.

The 'network' command is for OSPFv2 and does not exist in OSPFv3; interface configuration is done via interface commands.

Setting the network type to point-to-point changes the OSPF link type; without matching configuration on R2, adjacency will fail.

Mismatched hello intervals prevent OSPF neighbor relationships from forming.

The static default route has an administrative distance of 200, which is higher than OSPF’s 110. Therefore, it is less preferred and will not be installed while the OSPF route is present, making this option incorrect.

Cisco routers do not perform per-packet load balancing between routes with different administrative distances. The route with the lowest AD is installed exclusively, so this option is incorrect.

Floating static routes do not suppress dynamic routes; instead, they serve as backups when dynamic routes are unavailable. Therefore, neither route is not installed is incorrect because the OSPF route will be installed.

Both routers are configured in area 0, so area mismatch is not the cause. Area mismatches prevent neighbor discovery, which would stop adjacency formation before ExStart.

If one interface is passive, OSPF hello packets are not sent, preventing neighbor formation altogether. This would stop adjacency formation earlier than ExStart.

The subnet mask is consistent on both sides, allowing neighbor discovery. Incorrect subnet masks would prevent neighbors from recognizing each other, blocking adjacency before ExStart.

Common misconception that metrics are compared across different routing protocols. In reality, AD is evaluated first, and only routes from the same protocol with equal AD are compared by metric.

Mistaking ECMP as the mechanism for selecting between two routes from different sources; in this scenario, the static route's AD disqualifies the OSPF route entirely.

Misunderstanding that IP addresses, not administrative distance or metrics, influence path selection.

The 'summary-address' command is not valid for OSPF; it is used in EIGRP and BGP.

The 'ip summary-address ospf' command is used for external route summarization, not for summarizing internal OSPF routes within an area.

The mask 255.255.255.0 is too specific and only covers a single /24 network, not the required range.

The specific factual error is that the instruction limits changes to R1 only; modifying R2 is not allowed.

The specific factual error is that the dead interval is not automatically derived from the hello interval; it must be set separately.

The specific factual error is that the hello interval is not automatically derived from the dead interval; both must be set explicitly.

Incorrect timers (30/120) break adjacency, and 'passive-interface default' suppresses hellos on all interfaces, including the transit link.

Network type point-to-point on R1 does not match R2's default broadcast, causing a type mismatch that prevents OSPF adjacency.

Omits the required 'passive-interface GigabitEthernet0/1' command, leaving hellos sending on that interface.

The network statement is syntactically correct and covers the interface IP address, so it does enable OSPF process on that interface (subject to the passive-interface setting).

The configuration shows 'no shutdown', indicating the interface is enabled. Administrative down would require the 'shutdown' command or lack of 'no shutdown'.

The output clearly shows 'area 0' in both routers' OSPF configurations, so area mismatch is not the cause.

Candidates may confuse adjacency failures with DBD exchange problems, but network type mismatch leads to a different state (2-WAY).

Candidates think duplicate Router IDs might cause DBD exchange failure, but duplicate IDs prevent neighbor discovery entirely.

Many associate EXSTART with any adjacency issue, but authentication errors prevent the neighbor from being listed at all.

This option is incorrect because metric values are only compared among routes learned from the same routing protocol. The OSPF metric of 30 is irrelevant when compared to a static route, which is a different routing source with a lower administrative distance.

This option is incorrect because routers do not install multiple routes to the same prefix from different routing protocols unless they have equal administrative distance and are configured for load balancing. Here, the static route’s lower AD prevents the OSPF route from being installed.

This option is incorrect because the router does not delay route installation until a full SPF recalculation. Route selection is immediate based on administrative distance and metric rules. SPF recalculation only affects OSPF route selection, not cross-protocol comparisons.

Option A incorrectly states that 'O IA' is an external route redistributed from another routing protocol. In reality, 'O IA' stands for inter-area routes within OSPF, not external routes. External routes use 'O E1' or 'O E2' codes.

Option C incorrectly claims that 'O' means the route was learned through EIGRP. The 'O' code is exclusive to OSPF intra-area routes. EIGRP routes use the code 'D' in Cisco routing tables.

Option D is incorrect because the three routes represent different OSPF route types: intra-area (O), inter-area (O IA), and external (O E2). They do not all come from the same OSPF area type.

The router-id is used only for OSPF router identification and does not need to be reachable; adjacency uses interface IP addresses.

OSPF does not require a specific subnet mask; it uses the configured mask on the interface as the network type.

OSPF is enabled on R2's G0/0; the issue is on R1's side where the passive-interface prevents hellos.

Candidates may attribute arbitrary high metrics to a bandwidth calculation error, without noticing that only one LSA is affected.

A misunderstanding that filtering can somehow alter the metric rather than block the advertisement completely.

Confusion between external and inter-area route types leads candidates to think that metric-type manipulation could affect an internal summary LSA.

Area mismatch is a valid cause but not supported by the given data; the IP addresses are on different subnets, which logically precedes area negotiation.

MTU is not shown; candidates may recall that mismatched MTU can cause OSPF problems but the scenario explicitly reveals an IP addressing inconsistency.

Authentication issues are common OSPF traps, but they are not indicated here; the IP address difference is explicitly observed.

The specific factual error is that OSPFv3 uses interface-level configuration, not network statements under the OSPF process.

The specific factual error is that setting a router ID alone does not activate OSPFv3 on an interface; OSPFv3 must be explicitly enabled on the interface.

The specific factual error is that 'passive-interface default' would actually prevent adjacency, not help form it.

Different hostnames do not affect OSPF adjacency since hostnames are used only for identification and management, not neighbor formation.

Different loopback addresses used for management do not influence OSPF adjacency on Ethernet interfaces, so they do not block neighbor relationships.

One router using SSH version 2 is unrelated to OSPF adjacency because SSH is a management protocol and does not impact routing protocol neighbor formation.

Candidates may think network type mismatch when they see no adjacency, but the exhibit does not indicate a mismatch and explicitly shows the passive state.

Timer mismatch is a classic troubleshooting trap, but the 'No Hellos (Passive interface)' message overrides any timer considerations.

Candidates may guess area mismatch as a cause, but the exhibit provides no evidence of it, while the passive-interface message is a direct cause.

A priority of 255 is the highest possible value, ensuring the router becomes the DR or BDR, not excluding it.

Priority 1 is the default and allows the router to be elected if it has the highest priority or Router ID.

Loopback interfaces are not used for DR/BDR elections; they are logical interfaces. The priority must be set on the physical interfaces connecting to other routers.

Administrative distance is only compared when two routes have the same prefix length. Here, the /32 route has a longer prefix, so it is chosen first.

Load balancing requires routes with identical prefix lengths and metrics. The /32 and /24 routes are treated as different destinations.

AD is only compared when routes have the exact same prefix length. The routing table can hold multiple overlapping routes as long as they differ in prefix length.

Incorrect because OSPF can handle multiple equal-cost routes and does not discard them; it uses all equal-cost paths to improve traffic distribution.

Incorrect since OSPF does not keep only the first learned route when multiple equal-cost paths exist; it installs all such routes for load balancing.

Incorrect because OSPF does not replace multiple valid equal-cost routes with a default route; default routes are used only when no specific routes exist.

Misunderstanding of route preference: a higher AD value does not keep a floating static installed when a better OSPF route becomes available.

Troubleshooting should follow the OSI model bottom‑up; immediately resetting processes skips basic interface‑level verification.

It targets a different root cause (OSPF adjacency failure due to MTU) that would manifest constantly, not only after interface recovery.

This option is wrong because a static route with a lower administrative distance than OSPF would take precedence over OSPF routes, making it active even when OSPF is available, contrary to the requirement of using the static route only when the OSPF route is unavailable.

This option is wrong because a second OSPF route with a lower metric would not serve as a backup to the existing OSPF route; instead, it would be preferred over the static route, which contradicts the requirement for the static route to be used only if the OSPF route disappears.

A default route with no next hop would not serve as a backup for an OSPF route because it lacks specificity and cannot direct traffic to a specific network. It would be ineffective in scenarios where a specific static route is needed when OSPF fails.

The question says R3 advertises the network via OSPF; a missing network command would contradict that, so the failure must be in adjacency formation.

The presence of other OSPF routes on the same interface disproves a blanket multicast ACL; the issue is specific to R3’s adjacency.

A duplicate router ID could prevent adjacency, but the scenario’s focus on passive-interface default provides a more common and direct cause for a total lack of adjacency when OSPF is correctly configured on the network.

Incorrect. OSPFv3 forms adjacencies using IPv6 link-local addresses, so global unicast addresses are not mandatory for adjacency formation or neighbor discovery.

Incorrect. Router IDs must be unique identifiers for OSPF routers. Identical router IDs cause adjacency failure, but they do not need to be identical to form adjacency.

Incorrect. IPv6 link-local addresses are automatically configured on interfaces and do not require DHCPv6. OSPFv3 uses these link-local addresses for neighbor communication.

OSPFv3 requires the link interface to be enabled to form neighbors; loopback-only configuration results in no neighbor relationship.

OSPFv3 must be enabled on the loopback interfaces to advertise their prefixes; otherwise, they remain unknown to the neighbor.

Both routers must have OSPFv3 enabled on the link interface to form an adjacency, and both loopbacks must be enabled to advertise their prefixes.

This option is wrong because the OSPF route to 10.60.4.0/24 does not directly match the destination 10.60.4.17, which falls under the static route to 10.60.4.16/28. OSPF would not be preferred if a more specific static route exists.

The EIGRP route to 10.60.0.0/16 is not used for the destination 10.60.4.17 because it does not match the more specific subnet of 10.60.4.16/28, which is preferred in routing decisions.

This option is wrong because there is a valid static route to the destination 10.60.4.17 via the static route to 10.60.4.16/28, making it reachable. Therefore, stating 'no route at all' is incorrect in this context.

This option is incorrect because both routers are configured to use the same OSPF area 0, so area mismatch is not the cause of adjacency failure.

Hostnames do not influence OSPF neighbor relationships; routers form adjacencies based on protocol parameters, not device names, so this option is invalid.

A /24 subnet mask does not block OSPF multicast traffic; OSPF uses multicast addresses that function normally on standard subnet masks, so this option is incorrect.

The specific factual error is that the question implies you are connected to R1, so configuring R1 is the expected action. Additionally, using area 1 instead of area 0 is not recommended for a single-area design.

The specific factual error is that the timers are not changed to match R2; they remain at the original values.

The specific factual error is that R2's area is already 0, so changing it to area 0 is redundant. Changing R2's timers to match R1's original timers would still leave a mismatch because R1's timers are not changed.

The OSPF route to 10.30.5.0/24 is less specific than the /25 static route, so the router prefers the longest mask.

The default route (0.0.0.0/0) has the shortest prefix length and would be used only if no other route matches.

10.30.5.130 is inside the 10.30.5.128/25 subnet range, meaning a route exists for this destination.

Router-ID mismatch does not block OSPF adjacency; an OSPF router can still form a neighbor relationship even if the router-ID is not explicitly set (it will use the highest loopback IP) and can be changed without issue.

Network type mismatch would prevent adjacency, but the scenario does not indicate a mismatch; the default for Ethernet is broadcast, so both should be broadcast, and if one were changed to point-to-point they would not form, but that is not stated.

Passive-interface on the link interface (G0/0) would suppress hello packets and prevent adjacency, but the configuration correctly has passive-interface only on loopback0, so this is not the problem.

A wildcard mask of 0.0.0.0 only matches one exact IP address. It does not impose any restriction on adjacency.

Passive interfaces still advertise their networks—they just do not send or receive Hello packets. Only adjacency is suppressed.

The network command matches multiple interfaces; OSPF then tries to form adjacencies on every enabled interface, regardless of IP address order.

This option incorrectly assumes that the router compares OSPF metric 20 directly against EIGRP feasible distance 30720 to select the route. Cisco routers do not compare metrics across different routing protocols; they use administrative distance first. Therefore, this option is incorrect.

This option incorrectly claims that both routes are installed due to automatic ECMP across different protocols. Cisco routers do not perform equal-cost load balancing between different routing protocols without explicit redistribution or configuration, so this is false.

This option incorrectly states that neither route is installed until redistribution occurs. Redistribution is not necessary for a router to install a route learned from a routing protocol. The router installs the route with the lowest administrative distance immediately, so this option is incorrect.

This option is wrong because OSPF allows multiple routers to have the same Router ID, but they can still form adjacencies if other parameters are correctly configured. The issue in this scenario is related to mismatched OSPF timers, not Router IDs.

This option is incorrect because the interface cost does not directly affect the formation of OSPF adjacencies; it only influences the route selection process once adjacencies are established.

The subnet mask being invalid is not the cause of the OSPF adjacency failure in this scenario, as the issue lies with the mismatch of OSPF timers rather than an incorrect subnet mask. Both routers are on the same segment and should have compatible subnet configurations.

The specific factual error is that the timers should be made consistent by adjusting R2 to match R1, not the other way around, and the area mismatch requires both routers to be in the same area, which is area 0.

The specific factual error is that the timers on R1 are already correct, and the area mismatch requires both routers to be in the same area. Changing R2's area to area 1 would not match R3's area 0.

Option C is incorrect because passive interfaces do not convert OSPF into static routing; OSPF remains active and continues to advertise routes.

Option D is incorrect because passive interface configuration does not influence router ID selection, which is determined by other OSPF rules.

Option E is incorrect because passive interface settings apply only to the specified interface and do not disable OSPF on all router interfaces.

The 'network' command is not valid for OSPFv3; OSPFv3 uses interface-level configuration.

This command is only valid in interface configuration mode.

The question explicitly says IPv6 unicast routing is already enabled, so this option includes an unnecessary step.

Incorrect because OSPF does not select a single route based on the highest router ID when multiple equal-cost paths exist; it installs all such routes.

Incorrect because OSPF explicitly supports equal-cost multipath (ECMP) routing and does not limit itself to installing only one route.

Incorrect because the next-hop IP address is not a factor in OSPF’s path selection among equal-cost routes; cost metric is the deciding factor.

Setting the static route metric lower than the OSPF cost is ineffective because Cisco routers compare administrative distance first across different routing sources.

Configuring the route as directly connected with no next-hop information would give it an administrative distance of 0, making it preferred over OSPF, which is not the behavior of a floating static route.

This option is incorrect because static routes do not always win over dynamic routes; the route with the lowest administrative distance is preferred. In this case, OSPF has a lower administrative distance (110) than the floating static route (130).

This option is incorrect because only one route can be installed in the routing table for a specific prefix, and in this case, OSPF has a lower administrative distance than the floating static route, so only the OSPF route will be installed.

This option is incorrect because OSPF is healthy and has a lower administrative distance than the floating static route, meaning the OSPF route will be preferred and installed in the routing table.

The specific factual error is that changing network type is unnecessary and does not fix the passive-interface or timer mismatch problems.

The specific factual error is that the network command is already configured, so adding it again does not solve the adjacency problem.

The specific factual error is that loopback interfaces are intentionally excluded from OSPF, and forcing them to participate is not required and would be incorrect.

Incorrect because router hostnames do not affect OSPF adjacency formation. OSPF neighbors identify each other by router IDs and interface parameters, not hostnames.

Incorrect because OSPF supports various subnet masks and does not require a /24 subnet. The problem is related to timer mismatch, not subnet size.

Incorrect because static routes are not necessary for OSPF adjacency. OSPF dynamically discovers neighbors using hello packets and forms adjacencies based on protocol parameters.