N10-009 Question 138
Single answer2.1 Explain characteristics of routing technologies.A company is merging two branch offices into its WAN. The network team wants routing to adapt automatically if a WAN link fails, but they also want to prevent routers from learning unnecessary routes from an ISP connection. At one branch, the router should send all unknown traffic toward the ISP while continuing to use dynamically learned internal routes for corporate subnets. Which routing approach best meets these requirements?
- A
Configure a default route toward the ISP and use a dynamic routing protocol internally between company routers
- B
Configure only static routes for every internal and external network on all routers
- C
Advertise the ISP routes into the internal network using a distance-vector protocol so all routers learn every possible path
- D
Disable dynamic routing and rely on link-state forwarding tables learned from the ISP
Show answer and explanation
Correct answer: A
Explanation
The best solution is to use dynamic routing internally and a static default route toward the ISP. This approach matches common enterprise routing design: internal routes are exchanged automatically so routers can adjust to topology changes, while the default route handles all unknown destinations without requiring the enterprise to learn full or partial Internet routing information. In Network+ terms, this tests the characteristics of static routing, dynamic routing, and default routes. Static routes are simple and predictable but require manual updates. Dynamic routing protocols automatically share route information and reconverge after failures. A default route is ideal when traffic to unknown networks should be forwarded to a single upstream gateway, such as an ISP. This aligns with common vendor documentation and best practices from enterprise routing design guidance, where default routing is used at the network edge and dynamic routing is used within the organization for resiliency and scalability.
- A. Correct.
Correct. This design combines a static default route (also called a gateway of last resort) for unknown destinations with dynamic routing for internal corporate networks. This is a common best practice in enterprise networks: dynamic routing protocols such as OSPF or EIGRP are used to exchange internal routes and automatically reconverge after link failures, while a default route sends Internet-bound traffic to the ISP without importing unnecessary external routes.
- B. Incorrect.
Incorrect. Using only static routes would require manual configuration for every network and would not scale well during a branch merger. It also does not meet the requirement for automatic adaptation to WAN link failures unless administrators manually update routes. Static routing is useful in small, stable environments, but it is not the best choice here.
- C. Incorrect.
Incorrect. Advertising ISP routes into the internal network would increase routing-table size and complexity and violates the requirement to avoid learning unnecessary routes from the ISP. A candidate might choose this option because dynamic routing sounds adaptive, but in this scenario the simpler and more appropriate method is to use a default route for external traffic.
- D. Incorrect.
Incorrect. ISPs do not provide 'link-state forwarding tables' for customer routers in the way described here, and disabling dynamic routing would remove the automatic failover behavior required for internal WAN links. This option reflects a misunderstanding of how routing protocols and provider handoffs typically work in enterprise networks.