CCNA Interior Gateway Protocols Questions

The NSSA is the OSPF area type whose ABR translates Type-7 LSAs into Type-5 LSAs, and it is the only standard area type that generates Type-7 LSAs internally. This satisfies the question's requirement for an area permitting Type-7 LSA generation.

`show ospf neighbour` displays adjacency states and the router IDs of peers, exposing stuck ExStart or Exchange states that indicate MTU mismatches or mismatched authentication. This directly satisfies the stem's requirement for an OSPF troubleshooting command, since neighbour formation failures are the most common cause of missing routes.

OSPFv3 removed IPv6 addresses from Router and Network LSAs, so prefix information is carried separately by the Intra-Area-Prefix LSA, Type 9. It associates prefixes with a referenced Router, Network or Link LSA within the same area, satisfying the requirement for intra-area IPv6 prefix propagation.

`show ospf database` dumps the OSPFv2 link-state database, listing router LSAs and network LSAs with their link-state IDs, advertising routers, sequence numbers and ages. It directly satisfies the stem's requirement to display LSAs, unlike neighbour or interface commands that show adjacency state or timer values instead.

Junos separates routing information by protocol, so the protocol qualifier filters the routing table to only OSPF-learned prefixes. This directly satisfies the requirement to examine OSPF entries specifically, rather than the full inet.0 table containing connected, static and other protocol routes.

The command applies MD5 authentication directly under the OSPFv2 interface stanza, satisfying the requirement for cryptographic authentication on that specific interface. The key ID (1) and key string follow the `authentication md5` keyword, which Junos requires to generate the MD5 digest for OSPF hello and link-state packets.

The 'restrict' option prevents the summary LSA from being injected into the area.

If the forwarding address in the external LSA is not reachable, OSPF will not install the route. The forwarding address is used to avoid extra hops, and if it cannot be resolved, the route is considered invalid. This is a common cause for external routes not being installed despite being in the LSDB.

This command correctly generates a Type 7 default LSA into the NSSA area with the specified metric.

Junos defaults redistributed routes entering OSPF to external metric-type 2 with a cost of 1, so the route is advertised without accumulating internal OSPF link costs. Type 1 would add internal costs, which is not the default behaviour.

Type-7 LSAs are specifically designed for NSSAs to originate external routes without accepting Type-5 LSAs from the backbone.

This statement enables OSPFv3 on the specified interface and associates it with area 0. OSPFv3 is configured under the [edit protocols ospf3] hierarchy in Junos OS. Without this interface-level configuration, OSPFv3 will not run on the interface, even if IPv6 is enabled. This is the correct and required step to activate OSPFv3 on an interface.

Junos OS sets the OSPF reference bandwidth to 100 Mbps by default, so any interface at or above that speed receives a cost of 1. Administrators must raise this value on faster links to preserve meaningful cost differentiation.

OSPFv3 is configured under protocols ospf3.

OSPF designated router election is decided first by interface priority, then router ID. Setting priority 200 on the interface raises it above the default 128, ensuring this router wins the DR election within area 0.0.0.0.

A stub area blocks Type-5 external LSAs at its boundary, so internal routers hold smaller link-state databases. The ABR instead injects a default route, giving stub routers reachability to external destinations without carrying external prefixes.

The 'translator-role never' command disables the NSSA ABR from performing Type-7 to Type-5 translation.

OSPF requires that the hello and dead intervals match on both routers for an adjacency to form. In this scenario, R1 has hello 10 and dead 40, while R2 has hello 30 and dead 120. Changing R1 to match R2's timers will allow the routers to establish the adjacency. This is a common configuration requirement in OSPF.

Type 4 ASBR Summary LSAs advertise the route to an ASBR and are flooded by the ABR into normal stub areas. Totally stubby areas block them, alongside Type 3 and Type 5, leaving only intra-area routes and a default.

Sham-links use /32 source and destination addresses inside the VPN routing instance.

The export policy's metric action assigns the OSPF external metric carried in the AS-external LSA when redistributing routes into OSPF. This satisfies the stem's requirement, letting the filter control the advertised cost of redistributed routes rather than relying on defaults.

Cryptographic authentication prevents unauthorized routers from forming adjacencies.

Junos displays each OSPF neighbour's router ID, interface and state (Init, 2-Way, ExStart, Exchange, Loading, Full) via this operational command, directly satisfying the stem's requirement to verify adjacency progress and confirm whether routers reached the Full state.

During ExStart, OSPF routers negotiate the master/slave relationship and exchange database description packets. If the interface MTU values differ, the routers cannot agree on the initial sequence number and the adjacency stalls in ExStart. This is a common cause and is resolved by matching the MTU on both interfaces or using the 'ignore-mtu' configuration.

Junos sets the OSPF reference bandwidth under the [edit protocols ospf] hierarchy, so the global command is set protocols ospf reference-bandwidth 10g. This raises the baseline used for cost calculation, giving accurate metrics for high-speed interfaces.

The 'priority' statement under the OSPF interface sets the DR election priority. A higher priority increases the likelihood of becoming the DR. Setting it to 100 (the maximum is 255) makes this router more likely to be elected DR than routers with lower priorities. This is the correct way to influence the DR election on a Junos device.

The interface-level 'cost' statement under the OSPF area hierarchy sets the metric advertised for that interface, directly influencing shortest-path calculation. This satisfies the requirement to adjust OSPF cost on a specific interface to manipulate path selection.

OSPFv3 runs as a separate routing process, so Junos uses the `protocols ospf3` hierarchy rather than `protocols ospf` with an address family. Assigning the interface under `area 0.0.0.0` enables OSPFv3 on that interface, satisfying the stem's requirement for the OSPFv3 address-family hierarchy.

The area-range statement under the area configuration on an ABR summarizes routes from that area into other areas. Configuring area-range under area 1 will summarize the routes from area 1 into area 0. This is the correct way to perform inter-area route summarization in OSPF on Junos.

The `database-overflow limit` parameter caps external LSAs at 5000, triggering overflow state once exceeded, while `external-timer 300` holds the router in that state for 300 seconds before retrying. This directly satisfies the stem's requirement to prevent memory exhaustion from excessive external LSAs, applied globally under `protocols ospf`.

The no-translate option on the NSSA ABR stops that router translating Type-7 LSAs into Type-5, leaving translation to the other ABR. This prevents duplicate Type-5 LSAs flooding the backbone, satisfying the requirement to suppress translation on one ABR.