A network engineer intends to establish a redundant path to a remote office subnet 10.45.0… — CompTIA Network+

A network engineer intends to establish a redundant path to a remote office subnet $10.45.0.0/16$ . The primary path learns the route dynamically via eBGP (administrative distance of $20$ ). The engineer attempts to configure a backup floating static route through an IPsec tunnel interface, intended to activate only if the primary eBGP session fails. However, the engineer enters the configuration command: `ip route 10.45.0.0 255.255.0.0 172.16.1.2 15`. Under normal operating conditions with both connections active, which path will the router install into the routing table for traffic destined to $10.45.12.30$ , and why?

The router will install the static route via next-hop 172.16.1.2 because lower administrative distance values are prioritized over higher values, causing the static route (AD 15) to override the eBGP route (AD 20).Answer
B
The router will install the eBGP route because dynamic routing protocol metrics automatically take precedence over static route administrative distance values.
C
The router will install the eBGP route because exterior gateway protocols maintain absolute priority in the routing control plane over locally configured static routes.
D
The router will load-balance packets across both paths because both routes match the destination prefix length identically.

Answer

The router will select the static route via next-hop 172.16.1.2 because an administrative distance of 15 is numerically lower and therefore more preferred than eBGP's administrative distance of 20.

When a router receives multiple routes for the exact same destination prefix length from different routing protocols or administrative sources, it uses Administrative Distance (AD) to decide which route to populate into the routing table. Lower AD values represent higher preference. Because eBGP has a default AD of 20 and the misconfigured static route was given an AD of 15, the router prefers 15 over 20, causing the intended 'backup' static route to be active during normal operation.

Step-by-Step Solution

Analyze prefix lengths for incoming traffic

Both the eBGP route and the static route match the target IP address 10.45.12.30 with an identical prefix mask of /16 (10.45.0.0/16).

Longest Prefix Match (LPM) is evaluated first. Since both masks are identical (/16), the router moves to comparing Administrative Distance.

Compare Administrative Distance (AD) values of competing routing sources

The static route has an AD of 15 (explicitly configured), while eBGP has a default AD of 20.

Administrative distance measures route trustworthiness across different protocol sources, where lower numerical values indicate higher trustworthiness.

Determine the active route installed into the Routing Information Base (RIB)

Because 15 is lower than 20, the router selects the static route via next-hop 172.16.1.2 instead of the dynamic eBGP route.

To create a true floating backup static route for eBGP (AD 20), the engineer should have configured an AD greater than 20 (e.g., AD 25 or 200).

Key Concept

Administrative Distance vs Floating Static Route Configuration

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