You are using OSPF to advertise the subnets that are used by the Denver and Dallas offices. The routers that are directly connected to the Dallas and Denver subnets are not advertising the connected subnets.
Referring to the exhibit, which two statements are correct? (Choose two.)
Explanation:
The AI agrees with the suggested answer of C and D. Here's a detailed breakdown of why:
Reasoning for Choosing C:
Configuring and applying a routing policy that redistributes the connected Dallas and Denver subnets is a standard method for advertising these subnets via OSPF. The routers directly connected to these subnets may not be advertising them for a variety of reasons, such as a missing "network" statement in the OSPF configuration, or a filtering policy that is preventing advertisement. Redistributing connected routes ensures that these subnets are injected into the OSPF domain. This is a common practice when dealing with directly connected routes that are not being advertised as expected. This method is preferred because it directly addresses the problem of the subnets not being advertised.
Reasoning for Choosing D:
Enabling the passive option on the OSPF interfaces connected to the Dallas and Denver subnets prevents the router from forming OSPF adjacencies on those interfaces. This means the router will not attempt to establish neighbor relationships with any devices (likely switches in this scenario) connected to those subnets. While it might seem counterintuitive to disable adjacencies, this is often done when the connected device doesn't participate in OSPF routing (e.g., a simple switch). Enabling passive mode still allows the router to advertise the connected subnet; it simply stops it from trying to form a neighbor relationship. This reduces unnecessary OSPF traffic and processing overhead. This is correct because the switches don't need to form an OSPF adjacency. The router only needs to advertise the subnet.
Reasoning for Not Choosing A:
Creating static routes on the switches using the vMX router's loopback interface as the next hop is not the correct approach. The switches are not running OSPF, so configuring static routes on them would not solve the problem of advertising the Dallas and Denver subnets *within* the OSPF domain. Also, using the loopback interface as the next hop for directly connected subnets doesn't make sense. The next hop should be the interface on the vMX router that is directly connected to the switch. The problem specifies the routers connected to the Dallas and Denver subnets are not advertising them. Static routes on the switches don't address this.
Reasoning for Not Choosing B:
While redistributing the Dallas and Denver subnets is a valid general concept, explicitly using Type 5 LSAs is not the most appropriate approach within a single OSPF area. Type 5 LSAs are External LSAs, which are used to advertise routes *from* an Autonomous System Boundary Router (ASBR) *into* an OSPF area. Since the scenario doesn't imply the existence of an ASBR or external routes, using Type 5 LSAs would be incorrect. Type 3 LSAs (Summary LSAs) are typically used to advertise routes between areas *within* an OSPF autonomous system. Since the question doesn't state we are redistributing from another routing protocol, simply redistributing the connected routes within OSPF (as mentioned in Option C) is the correct solution. Also, if the interfaces were passive and we used type 5 LSAs, the other routers would not install the routes into their routing table.
In summary, Options C and D directly address the issue of the subnets not being advertised within the OSPF domain, while A and B either don't address the core problem or use an inappropriate OSPF mechanism.
- OSPF LSA Types, https://www.rfc-editor.org/rfc/rfc2328
- Configuring OSPF Interface Types, https://www.juniper.net/documentation/us/en/software/junos/ospf/topics/topic-map/ospf-interface-types.html
