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300-410 Practice Question: An engineer is troubleshooting a BGP peering…
An engineer is troubleshooting a BGP peering issue between two routers, R1 and R2, connected via a serial link. The BGP session is established, but routes are not being exchanged. The engineer checks the BGP configuration and sees that both routers have the 'neighbor' commands correctly configured. The output of 'show ip bgp summary' shows the session is in the Established state, but the prefix counts are zero. What is the most likely cause?
⚠ Common exam trap
The trap is assuming that an Established BGP session implies routes are being exchanged — candidates overlook that session establishment and route injection are independent, and pick authentication or version issues that would actually break the session.
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
✓
Neither router has any network statements or redistribution commands configured to inject prefixes into BGP.
A BGP session can reach the Established state purely through neighbor configuration and TCP/179 connectivity, but no prefixes will be exchanged unless routes are injected into BGP via network statements, redistribution, or aggregation. Zero prefix counts in 'show ip bgp summary' with an Established session is the classic signature of a missing route injection configuration. The session itself is healthy; the routing table is simply empty of BGP-advertised 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.
- ✓
Neither router has any network statements or redistribution commands configured to inject prefixes into BGP.
Why this is correct
With the session Established, TCP and capability negotiation succeeded, so the zero prefix counts point to the local RIB being empty. BGP only advertises what is injected via network statements, redistribution or aggregation; without any of these, no NLRI exists to send.
- ✗
The BGP session is using MD5 authentication, but the passwords do not match.
Why it's wrong here
MD5 password mismatch prevents the TCP session from establishing at all, so the peer would sit in Active or Idle rather than Established. Authentication is the correct focus when a session never comes up, not when it is up with zero prefixes exchanged.
- ✗
The routers have mismatched BGP versions.
Why it's wrong here
BGP version mismatch is negotiated during OPEN; if the versions were incompatible the session would fail to establish rather than reach Established. Version checking applies when peering cannot form, whereas here the session is up and only prefix exchange is missing.
- ✗
The update-source command is missing, causing the session to use the wrong interface.
Why it's wrong here
A missing update-source cannot cause this: the session already reached Established, so TCP connectivity and source addresses are working. It is tempting because update-source faults do break BGP peering, but that failure prevents the session forming, not route exchange after establishment.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.