Weight is a Cisco-proprietary attribute that is local to the router and not advertised to peers. If a route has a lower weight (default is 0 for learned routes) than another path from a different source (like an IGP or static route with a higher weight), it will not be preferred. Since the BGP session is up and the prefix is advertised, the most common local reason for an external route not being installed is that another existing route in the RIB has a higher weight, making BGP not select the external path. Weight is considered before Local Preference in the BGP path selection algorithm.

Not-So-Stubby Areas (NSSA) allow the injection of external routes in a limited fashion into a stub area. By placing the servers in an NSSA area, the path to those networks is determined by the single ABR that connects the NSSA to the backbone (Area 0). This design ensures that inter-area traffic to those servers always flows through that designated ABR, providing predictable and stable routing, which is the goal described in the scenario.

EIGRP, when configured on a Layer 3 EtherChannel (PortChannel) interface, forms a single neighbor adjacency across the logical bundle. OSPF, by contrast, would form a separate adjacency for each physical member link unless specific configurations like OSPF point-to-point network type are used on the bundle, which isn’t the default behavior. BGP typically uses loopback addresses as neighbors, not directly correlating to the bundle. Therefore, EIGRP provides the simplest and most intended operation over an EtherChannel from a routing protocol adjacency perspective.

In DMVPN Phase 3, the hub uses the ‘ip nhrp redirect’ command. This command tells the hub to send an NHRP Redirect message to the source spoke when it forwards traffic to a destination spoke, indicating that a direct path is available. The spokes, upon receiving this redirect, must have ‘ip nhrp shortcut’ configured to act on it and initiate the dynamic spoke-to-spoke tunnel. The scenario states spokes cannot talk to each other, but the hub sees them. The missing piece is the trigger from the hub, which is the ‘ip nhrp redirect’ command.

An IP SLA Operation is the core component that defines the type of probe and its parameters. You configure an operation (e.g., ‘ip sla 10’) and then define the type (e.g., ‘icmp-echo’, ‘udp-jitter’, ‘http’) and all its details like target, frequency, and thresholds. The Track Object then monitors the state (up/down) of this operation. The Reaction Configuration can define actions based on measured values within the operation, and the Action Configuration defines what to do if a tracked object state changes.

When a route goes Active, EIGRP sends queries to its neighbors to find a new path. If the network is not summarized, these queries can propagate extensively (a problem known as ‘query propagation’). The absence of route summarization at strategic points means the link flap at the branch causes queries to be sent throughout the entire EIGRP domain, slowing down convergence. Configuring summarization creates a boundary; routers behind the summary point will reply ‘network not reachable’ to queries for the summarized range, limiting the scope of the query and speeding up convergence.

In Cisco IOS IKEv2 configuration, the correct syntax within the ‘proposal’ sub-mode is ‘encryption ‘ and ‘integrity ‘. For AES-256, the keyword is ‘aes-256’. For SHA-384, the keyword is ‘sha-384’. The other options use incorrect syntax (aes-cbc-256, missing hyphens, or using spaces) which would be rejected by the CLI parser.

Link-local addresses (fe80::/10) are not unique outside a specific network segment. Therefore, when specifying a link-local address as a next-hop for a static route, the router must be told which interface to use to reach that link-local neighbor. This is done by appending the exit interface identifier (e.g., ‘GigabitEthernet0/1’) to the command. The full command would be: ‘ipv6 route 2001:db8:1:1::/64 GigabitEthernet0/1 fe80::1’.

The ‘show dmvpn’ command shows the state of the tunnel. The state ‘NHRP’ indicates that the NHRP registration process is complete. This means the spoke has successfully registered its public (NBMA) address with the hub via NHRP. It is a key state showing the control plane (NHRP) is up. A state of ‘UP/UP’ would indicate both the line protocol (mGRE) and NHRP are up. A state like ‘IKE’ would point to an IPsec issue, and a physical interface down would show as ‘down/down’.

Weight is a Cisco-proprietary attribute that is local to the router and not advertised to peers. If a route has a lower weight (default is 0 for learned routes) than another path from a different source (like an IGP or static route with a higher weight), it will not be preferred. Since the BGP session is up and the prefix is advertised, the most common local reason for an external route not being installed is that another existing route in the RIB has a higher weight, making BGP not select the external path. Weight is considered before Local Preference in the BGP path selection algorithm.0