Quick Answer
The answer is a static default route with a lower administrative distance. This occurs because the routing table already contains a static default route (AD of 1), which is far more trustworthy than the eBGP-learned default route (AD of 20). Even though the BGP route is valid in the BGP table, it is marked as not best since the static route is already installed, preventing the BGP route from being selected for the routing table. On the Cisco SPCOR 350-501 exam, this scenario tests your understanding of administrative distance as the tiebreaker between different routing sources, not BGP path attributes. A common trap is to look for BGP-specific issues like missing next-hops or prefix-list filters, when the real culprit is a simple static route already occupying the slot. Remember the memory tip: "Static beats BGP every time—AD 1 is the king of the hill."
This 350-501 practice question tests your understanding of architecture. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
An engineer is troubleshooting a BGP route propagation issue. The customer is receiving a default route from upstream provider, but the route is not being installed in the routing table. The BGP table shows the route is valid but not best. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
The next-hop is unreachable
Why wrong: That would make the route invalid, not just not best.
The route is filtered by an inbound route-map
Why wrong: If filtered, it would not appear in BGP table at all.
The BGP session is not established
Why wrong: If session down, route would not be in BGP table.
A static default route with lower administrative distance exists
Static route AD 1 < BGP AD 20, so BGP route is not best.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
A static default route with lower administrative distance exists
Option D is correct because a static default route with a lower administrative distance (e.g., 1) will be preferred over a BGP default route (AD 20 for eBGP). Even though the BGP route is valid in the BGP table, it is not installed in the routing table because the static route is more trustworthy. This is a common scenario where the routing table already has a better path, preventing the BGP route from becoming 'best' and being installed.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
The next-hop is unreachable
Why it's wrong here
That would make the route invalid, not just not best.
The route is filtered by an inbound route-map
Why it's wrong here
If filtered, it would not appear in BGP table at all.
The BGP session is not established
Why it's wrong here
If session down, route would not be in BGP table.
A static default route with lower administrative distance exists
Why this is correct
Static route AD 1 < BGP AD 20, so BGP route is not best.
Clue confirmation
The clue words "best", "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Cisco often tests the distinction between a route being 'valid' in the BGP table versus being 'best' and installed in the routing table, trapping candidates who assume a valid BGP route is automatically used for forwarding.
Detailed technical explanation
BGP selects the best path based on a multi-step decision process (e.g., highest weight, local preference, shortest AS-path). However, even after BGP selects a best path, the route must be installed in the routing table (RIB) only if it has the lowest administrative distance among all routing sources for that prefix. A static route with AD 1 will always beat eBGP (AD 20) or iBGP (AD 200). This behavior is defined in Cisco's implementation of the routing table manager (RTM), which compares AD values before installing any route.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
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FAQ
Architecture — This question tests Architecture — Read the scenario before looking for a memorised answer..
The correct answer is: A static default route with lower administrative distance exists — Option D is correct because a static default route with a lower administrative distance (e.g., 1) will be preferred over a BGP default route (AD 20 for eBGP). Even though the BGP route is valid in the BGP table, it is not installed in the routing table because the static route is more trustworthy. This is a common scenario where the routing table already has a better path, preventing the BGP route from becoming 'best' and being installed.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "best", "most likely". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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