A network administrator is configuring an edge router connected to two upstream service providers. The router learns a default route () via eBGP from ISP A with an Administrative Distance of 20 and a metric of 10. Simultaneously, the administrator configures a manual static default route pointing toward ISP B using the default Administrative Distance of 1. If both links are active and healthy, which path will the router install into its Routing Information Base (RIB) for default traffic?
- The static route pointing to ISP B, because static routes have a lower Administrative Distance than eBGP routes.Answer
- BThe eBGP route from ISP A, because dynamic routing protocols take precedence over manually configured static routes.
- CThe eBGP route from ISP A, because its metric of 10 is evaluated before Administrative Distance during path selection.
- DBoth routes equally, installing both paths into the routing table to perform equal-cost multipath load balancing.
Answer
The static route pointing to ISP B, because static routes have a lower Administrative Distance than eBGP routes.
When a router receives multiple candidate routes for the exact same network prefix () from different routing protocols or administrative sources, it compares their Administrative Distance (AD). Administrative distance rates trustworthiness, where lower numerical values indicate higher preference. Static routes default to an AD of 1, whereas external BGP (eBGP) routes have a default AD of 20. Because 1 is less than 20, the static route is selected and installed into the active routing table.
Step-by-Step Solution
Key Concept
Routing Table Path Selection & Administrative Distance Hierarchy