hardMultiple ChoiceObjective-mapped
300-410 R1 and R2 are eBGP peers Practice Question
R1 and R2 are eBGP peers. R1 advertises a summary route 10.0.0.0/8 via aggregate-address 10.0.0.0 255.0.0.0 summary-only. R2 receives the summary but also expects to receive more specific routes (e.g., 10.1.0.0/16) for traffic engineering. R2's BGP table shows only the summary, and the more specific routes are missing. R1's configuration includes: router bgp 65001, network 10.1.0.0 mask 255.255.0.0, and aggregate-address 10.0.0.0 255.0.0.0 summary-only. What is the root cause?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The summary-only keyword suppresses all more specific routes, including the network 10.1.0.0/16, from being advertised to R2.
The aggregate-address with summary-only suppresses all more specific routes from being advertised to neighbors. Even though the network 10.1.0.0/16 is injected into BGP, the summary-only keyword causes it to be suppressed from advertisements. To allow the more specific route to be advertised alongside the summary, the summary-only keyword should be removed, or the more specific route should be explicitly permitted via a route-map. The root cause is that summary-only suppresses the more specific routes.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The summary-only keyword suppresses all more specific routes, including the network 10.1.0.0/16, from being advertised to R2.
Why this is correct
summary-only causes all more specific routes to be suppressed, even if they are explicitly configured with network statements.
- ✗
The network 10.1.0.0/16 is not in the routing table of R1, so it cannot be advertised.
Why it's wrong here
The network statement requires a matching route in the routing table, but the issue is suppression, not absence.
- ✗
R2 must have a route-map to accept the more specific route.
Why it's wrong here
R2 does not filter inbound; the problem is on R1's outbound advertisement.
- ✗
The aggregate-address should be configured with the as-set keyword to include more specifics.
Why it's wrong here
as-set affects AS_PATH, not suppression of more specifics.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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