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An OSPFv2 router has no explicit router-id command. Loopback0 is 10.20.30.1/32 and Gi0/0 is 172.28.6.1/24; both are up when the process starts. Which router ID is chosen?
With no explicit router ID, Cisco IOS prefers a loopback IPv4 address even when a physical interface has a numerically higher IPv4 address.
Loopback preference overrides the ordinary highest-active-interface rule.
Process IDs are local numeric identifiers, not automatically used as router IDs.
A subnet mask is not substituted for the loopback interface address.
An OSPFv2 router starts without a manually assigned router ID or loopbacks. Its up/up interfaces are 10.1.1.1/24, 172.16.7.1/24, and 192.0.2.3/30. Which router ID is selected?
With no manual ID or loopback, IOS selects the highest up/up IPv4 interface address at process start; the first octet 192 exceeds 172 and 10.
Interface numbering is not the router-ID selection criterion.
Public versus private address classification does not drive automatic router ID choice.
IPv4 masks do not prevent normal router-ID selection from active addresses.
R1 has an established OSPFv2 process with router ID 10.10.10.10. An engineer adds a higher loopback 10.10.10.99. Which statement about the current OSPF router ID is accurate?
Router ID selection normally occurs at OSPF process initialization and is not automatically recomputed just because a higher address appears later.
Adding a higher loopback does not automatically replace a running OSPF router ID.
OSPF router ID is an identifier, not a host gateway function.
Adding a loopback is not intrinsically an adjacency failure event.
A network team reports that two OSPFv2 routers in the same routing domain show the same router ID and unstable neighbors. Which fix addresses the identity collision?
Router IDs must uniquely identify OSPF speakers within the domain; a collision can corrupt adjacency or LSA interpretation.
Switch speed cannot correct OSPF identity duplication.
Duplicating MAC addresses adds another conflict and does not establish unique OSPF router IDs.
More logs help diagnosis, but they do not remove the ID conflict.
R1 and R2 are single-area OSPFv2 neighbors. R1 is configured with `router ospf 10` and R2 with `router ospf 77`; both advertise their connected networks in area 0. Which statement is correct?
Cisco IOS OSPF process IDs are local identifiers; routers can form an adjacency despite different process numbers when link-level OSPF requirements match.
OSPF process numbers are not a common neighbor parameter transmitted as a matching requirement.
DR election is based on per-interface priority and router ID, not OSPF process number.
The router ospf command under IPv4 does not switch protocol families based on the process number.
R1 is configured to run single-area OSPFv2 but its Ethernet Gi0/1 is not sending Hellos although the interface is up. The configuration includes `passive-interface GigabitEthernet0/1`. Which change is appropriate if a neighbor is required there?
Passive interfaces do not send OSPF Hellos and therefore cannot establish neighbors on that interface; removing passive status permits Hello exchange.
Changing host prefix masks does not reenable OSPF Hellos.
Cost selection does not override passive-interface Hello suppression.
The router ID identifies the OSPF speaker but a passive OSPF interface still suppresses Hellos regardless of the chosen ID.
A branch LAN 10.30.40.0/24 must be advertised in OSPFv2 area 0 but no OSPF neighbors should form with access hosts on that LAN. What is a correct IOS design?
An OSPF passive interface remains advertised as a connected network by the process but stops generating Hellos toward host-facing access segments.
An interface outside the OSPF process is not automatically advertised just because it is connected.
Core links need Hello exchange to form OSPF adjacencies.
High DR priority does not suppress OSPF Hellos.
A router runs OSPFv2 area 0. Interface Gi0/1 is addressed 10.2.3.1/24. Which IOS network statement correctly selects that interface by its IPv4 subnet?
In Cisco IOS `network` statements use wildcard masks; 0.0.0.255 matches the /24 network 10.2.3.0 and activates OSPF on matching interfaces in area 0.
255.255.255.0 is a subnet mask, not the correct wildcard for the /24 match.
A static route command does not enable the interface in the OSPF process.
The displayed phrase is not valid IOS OSPF network-statement syntax.
An engineer wants to activate OSPFv2 area 0 directly on Gi0/0 without using a network wildcard statement. Which interface configuration is valid on supporting Cisco IOS?
The interface-level ip ospf process-id area area-id command activates that OSPF process on the interface, independent of a global network-match statement.
router ospf is a global routing-process configuration command, not an interface command.
IOS expects an OSPF process ID followed by the `area` keyword and area value.
ip route defines static routes; it does not enable interface OSPF participation.
Two single-area OSPFv2 routers have a neighbor relationship stuck in EXSTART/EXCHANGE after a new tunnel was introduced. IP connectivity and area/timers are otherwise correct. Which mismatch should the engineer check first?
OSPF database description packets include an interface MTU; inconsistent MTU handling can prevent successful database synchronization in EXSTART/EXCHANGE.
Process IDs are local and do not have to match during database description exchange.
Textual descriptions are not negotiated OSPF neighbor parameters.
Console authentication is unrelated to link-state database exchange.
An Ethernet OSPFv2 adjacency reaches 2-WAY state between two DROTHER routers on a broadcast network. The elected DR and BDR are healthy. What does 2-WAY typically indicate here?
On a broadcast multiaccess segment, DROTHER–DROTHER routers may remain in 2-WAY while FULL adjacency forms to the DR and BDR.
A 2-WAY state between two DROTHER devices is often expected.
Mismatched subnet parameters are different from the normal two-way neighbor discovery state.
A stable DR/BDR election is not preempted simply because two DROTHER peers see each other.
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