H12-891_V1-0 practice question 8 of 35

What type of prefix does a router running BGP advertise to its IBGP neighbor (assuming the router is not configured as a route reflector)? (radio).

Answer options

A: Prefixes are learned through other IBGP neighbors, or prefixes are learned from EBGP neighbors, or prefixes are learned through routing introduction

B: A prefix that exists in the routing table

C: Prefixes are learned through other BGP neighbors, or prefixes are learned locally through network or routing introduction

D: Prefixes are learned through EBGP neighbors, or prefixes are learned locally through network or routing introduction Correct answer

E: The prefix is learned through an EBGP neighbor, or the prefix is learned from an from RR

Correct Answer:

D. Prefixes are learned through EBGP neighbors, or prefixes are learned locally through network or routing introduction

Explanation

This question addresses the BGP split-horizon rule for Internal BGP (IBGP). To prevent routing loops within an Autonomous System (AS), a BGP router does not advertise routes learned from one IBGP peer to its other IBGP peers. Therefore, a router (not configured as a route reflector) will only advertise two categories of routes to its IBGP neighbors: 1) routes learned from External BGP (EBGP) peers, and 2) routes originated locally within its own AS (via the network command or by importing routes from an IGP).

Why Incorrect

A. This is incorrect because it includes routes "learned through other IBGP neighbors," which violates the IBGP split-horizon rule.
B. This is too generic. While the prefix must be in the routing table, this option does not specify the origin or BGP rules applied.
C. This is incorrect as "other BGP neighbors" is ambiguous and could include IBGP neighbors, violating the split-horizon rule.
E. This is incorrect because the question explicitly states the router is not a route reflector (RR), which is a mechanism to bypass the split-horizon rule.

References

1. Huawei HedEx Documentation, CloudEngine S12700 V200R019C10 Configuration Guide - BGP, Section: "BGP Fundamentals" -> "BGP Route Advertisement Rules". This section details the IBGP split-horizon rule, stating that routes learned from an IBGP peer are not advertised to other IBGP peers. It also confirms that routes from EBGP peers and locally originated routes are advertised.

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