Equal-AD Routes Cause R1 to Load-Balance to 172.16.1.4/30

200-301 By islever Editorial Last updated

Determine how a router makes a forwarding decision by default

Short answer

D Both next hops (172.16.9.5 and 172.16.4.4) have equal administrative distance, so R1 installs both and load-balances traffic to 172.16.1.4/30.

Question

Refer to the exhibit. How does router R1 handle traffic to 172.16.1.4 /30 subnet? - Exhibit: Equal-AD Routes Cause R1 to Load-Balance to 172.16.1.4/30
  1. It sends all traffic over the path via 172.16.9.5 using 172.16.4.4 as a backup.
  2. It sends all traffic over the path via 10.0.1.100.
  3. It sends all traffic over the path via 172.16.4.4.
  4. It load-balances traffic over 172.16.9.5 and 172.16.4.4 Correct Answer

Key Takeaways

Equal AD + equal metric = multiple equal-cost paths in the routing table = per-flow load balancing. AD is the first tiebreaker in the forwarding decision.

When a router has two routes to the same destination with the same administrative distance (and, after AD, equal metrics), it installs both and load-balances traffic across them. Here R1 sees 172.16.9.5 and 172.16.4.4 as equal-AD next hops, so it splits traffic to 172.16.1.4/30.

Common mistake: Assuming one path is a 'backup': with identical AD there is no primary/backup relationship; both are active and share the traffic.

Expert Analysis

Why the Answer Is Correct

D is correct. R1 has two routes to 172.16.1.4/30 whose next hops (172.16.9.5 and 172.16.4.4) share the same administrative distance. Because AD is the first tiebreaker and it is equal, R1 keeps both routes and load-balances traffic across them.

Why the Other Options Are Wrong

A and C pick only one of the two equal paths, ignoring the second. B names a next hop (10.0.1.100) that is not the equal-AD pair for this destination.

Community Comment Notes

The vote is D (100). A commenter asks why it load-balances and the answer is the equal AD on both paths.

Official Reference

https://learningnetwork.cisco.com/s/ccna-exam-topics

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Community Votes

D
100%

100% of anonymous learners picked answer D. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 3 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 3

  1. gunmandu1709 👍 2
    Someone can tell me why is it load balancing? Is it because they have same AD?
  2. eb63e5a 👍 1
    given answer is Exact
  3. 21c069a 👍 1
    D is correct

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