200-301 · Question #1080
200-301 Question #1080: Real Exam Question with Answer & Explanation
Administrative Distance & Route Selection — Explained This question tests your understanding of Administrative Distance (AD) — the trustworthiness metric routers use to choose between competing routes to the same destination. Lower AD wins. Key AD Values (memorize these) | Ro
Question
Drag and Drop Question Refer to the exhibit. The Router1 routing table has multiple methods to reach 10.10.10.0/24 as shown. The default Administrative Distance is used. Drag and drop the network conditions from the left onto the routing methods that Router1 uses on the right. Answer:
Explanation
Administrative Distance & Route Selection — Explained
This question tests your understanding of Administrative Distance (AD) — the trustworthiness metric routers use to choose between competing routes to the same destination. Lower AD wins.
Key AD Values (memorize these)
| Routing Method | Default AD |
|---|---|
| Static route | 1 |
| eBGP | 20 |
| EIGRP (internal) | 90 |
| OSPF | 110 |
Router1 has four ways to reach 10.10.10.0/24: Static, eBGP, EIGRP, OSPF. When multiple routes exist, the lowest AD among currently available routes wins.
Item-by-Item Breakdown
Position 4 — "All protocols are up" All four routes available. Static (AD 1) wins — it's the most trusted. Router uses the static route.
Position 5 — "OSPF and eBGP are down" Remaining: Static (1) and EIGRP (90). Static still wins. Router still uses the static route.
Same result as position 4, but now only two options remain.
Position 1 — "Static route and EIGRP are down" Remaining: eBGP (20) and OSPF (110). eBGP has lower AD. Router uses eBGP.
Position 2 — "Static route and OSPF are down" Remaining: eBGP (20) and EIGRP (90). eBGP still wins. Router uses eBGP.
Both positions 1 and 2 result in eBGP — because eBGP (20) always beats OSPF (110) or EIGRP (90).
Position 3 — "Static route and eBGP are down" Remaining: EIGRP (90) and OSPF (110). EIGRP wins. Router uses EIGRP.
Summary Logic
| Condition | Available Routes | Winner (Lowest AD) |
|---|---|---|
| All up | Static(1), eBGP(20), EIGRP(90), OSPF(110) | Static |
| OSPF + eBGP down | Static(1), EIGRP(90) | Static |
| Static + EIGRP down | eBGP(20), OSPF(110) | eBGP |
| Static + OSPF down | eBGP(20), EIGRP(90) | eBGP |
| Static + eBGP down | EIGRP(90), OSPF(110) | EIGRP |
Common Mistakes
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Confusing AD with metric. AD compares between routing protocols. Metric (cost, hop count, bandwidth) compares routes within the same protocol. They are completely separate concepts.
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Thinking OSPF beats EIGRP. OSPF (110) has a higher AD than EIGRP (90), so EIGRP is preferred — even though OSPF is often considered more "enterprise." Higher AD = less trusted.
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Forgetting eBGP vs iBGP. eBGP (external BGP) has AD 20. iBGP (internal BGP) has AD 200. This question uses eBGP — a very common exam gotcha. iBGP would lose to almost everything.
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Assuming the static route always wins. It does — unless it's explicitly stated as "down." When the static route is gone, you fall back to the next lowest AD, which is eBGP (20).
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