Which EIGRP Stub Mode Advertises All Needed Prefixs to Neighbors?
An engineer must configure a Cisco router by using the EIGRP stub command to ensure that adjacent neighbors receive all the necessary prefixes. Which EIGRP stub mode must be used to meet this requirement?
Community Insight
The question tests the EIGRP stub advertisement control keywords; the trap is assuming the default stub (connected + summary) or the 'connected' keyword already satisfies neighbors that require learned/leaked routes.
EIGRP's stub feature normally limits what a router advertises, but the leak-map option lets a stub router deliberately re-advertise specific suppressed prefixes to adjacent neighbors. This page establishes that 'eigrp stub ... leak-map <map>' is the only listed option that lets neighbors keep receiving all the prefixes they need.
Option D (connected) is the most tempting wrong pick because connected routes are part of the default stub advertisement, but that keyword only permits directly connected and summary routes and still suppresses everything else the neighbors need.
Community Discussion (2 comments)
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Expert Analysis
Why the Answer Is Correct
The leak-map keyword is applied as eigrp stub [connected|summary|static|redistributed|leak-map <map>] and it works by naming a route-map whose permit entries identify exactly which normally-suppressed routes the stub router will still advertise to its neighbors. Because a stub router by design stops answering queries and filters its outbound updates, the leak-map is the designated mechanism for carving out an exception list so downstream neighbors continue to receive specific prefixes they depend on. That is precisely the stated requirement — neighbors must receive all the necessary prefixes while the router remains a stub — so leak-map is the only option that satisfies it. As mohdx pointed out, the default stub (connected + summary) suppresses other prefixes, and that suppression is exactly what must be worked around. Applying the leak-map with a permit route-map gives deterministic, scalable control of what is released.
Why the Other Options Are Wrong
Option B, receive-only, is the opposite of what is required: it allows the router to receive routes but forbids it from advertising any routes at all, so adjacent neighbors would get nothing. Option C, redistribute, is a separate stub keyword that governs whether redistributed (externally learned) routes are advertised, and it addresses only that route class rather than the general set of prefixes neighbors need. Option D, connected, is merely a restriction keyword that permits only directly connected and summary routes, which is essentially the default behavior and still hides the other prefixes. None of these three provides the selective re-advertisement exception that the scenario demands.
Community Comment Notes
The community converged on option A, with mohdx explaining that "By default (eigrp stub with no options = connected + summary), the stub router only advertises connected and summary routes" and that this "suppression can block prefixes that downstream neighbors actually need." That reasoning matches Cisco's documented behavior of the leak-map keyword, and e14efdb explicitly stated "I fully agree," so the vote here aligns with the technical analysis rather than contradicting it.
Exam Strategy
When you see an EIGRP stub question that stresses what neighbors must still receive, look for the exception mechanism (leak-map) rather than a restriction keyword (connected, summary, static, redistributed, receive-only). Remember that every other stub keyword narrows advertisement, while only leak-map widens it under route-map control.
Frequently Asked Questions
Why doesn't 'eigrp stub connected' let neighbors receive all necessary prefixes?
The connected keyword only permits directly connected and summary routes to be advertised, which is the stub default; all other learned prefixes remain suppressed.
What does a leak-map do on an EIGRP stub router?
It is a route-map referenced by the stub command whose permit entries name the routes the stub router will still advertise to neighbors instead of suppressing them.
Why is receive-only the worst fit for this requirement?
receive-only makes the router advertise nothing at all, so adjacent neighbors would receive no routes, failing the requirement outright.
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