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350-501 · Question #303

Refer to the exhibit. An engineer working for a private telecommunication company with an employee id: 3414:81:713 is implementing this network, in which: - Routers R1A and R1B are eBGP neighbors…

The correct answer is C. Configure router R2A as a route reflector to advertise the iBGP learned prefix from router R3A to. Due to the iBGP split-horizon rule, R2A will not advertise prefixes learned from R1A to R3A; therefore, R2A must be configured as a route reflector to ensure all iBGP peers in the AS receive the advertised routes.

Networking

Question

Refer to the exhibit. An engineer working for a private telecommunication company with an employee id: 3414:81:713 is implementing this network, in which:

  • Routers R1A and R1B are eBGP neighbors.
  • iBGP is configured within AS 65515 and AS 65516.
  • Network 192.168.2.0/24 is shared with AS 65516.
  • Router R3A has an iBGP relationship with router R2A only.
  • Router R2A has an iBGP relationship with routers R1A and R3A.

Which additional task must the engineer perform to complete the configuration?

Exhibit

350-501 question #303 exhibit

Options

  • AConfigure router R2A to use the next-hop-self attribute when advertising the learned route to
  • BConfigure router R3A to redistribute route 192.168.2.0/24 into the configured IGP to advertise the
  • CConfigure router R2A as a route reflector to advertise the iBGP learned prefix from router R3A to
  • DConfigure router R1A with a static route to 192.168.2.0/24 that is redistributed into BGP.

How the community answered

(62 responses)
  • A
    11% (7)
  • B
    2% (1)
  • C
    84% (52)
  • D
    3% (2)

Why each option

Due to the iBGP split-horizon rule, R2A will not advertise prefixes learned from R1A to R3A; therefore, R2A must be configured as a route reflector to ensure all iBGP peers in the AS receive the advertised routes.

AConfigure router R2A to use the next-hop-self attribute when advertising the learned route to

The `next-hop-self` attribute is typically used to ensure the next-hop for a route is reachable within the AS, but the primary issue preventing route advertisement between R1A and R3A via R2A is the iBGP split-horizon rule.

BConfigure router R3A to redistribute route 192.168.2.0/24 into the configured IGP to advertise the

Redistributing a BGP-learned route into an IGP on R3A would not solve the problem of R3A receiving the BGP prefix itself if R2A doesn't reflect it due to split-horizon, and is generally discouraged due to potential routing issues.

CConfigure router R2A as a route reflector to advertise the iBGP learned prefix from router R3A toCorrect

The iBGP split-horizon rule prevents a BGP router from advertising prefixes learned from one iBGP peer to another iBGP peer. In this topology, R2A learns 192.168.2.0/24 from R1A (an iBGP peer) and would not advertise it to R3A (another iBGP peer). Configuring R2A as a route reflector allows it to reflect routes between its clients (R1A and R3A), ensuring R3A receives the 192.168.2.0/24 prefix.

DConfigure router R1A with a static route to 192.168.2.0/24 that is redistributed into BGP.

Configuring a static route on R1A to 192.168.2.0/24 that is then redistributed into BGP would make R1A the origin of the route, not AS 65516, and would not address the iBGP split-horizon issue preventing R3A from learning the route from its true origin.

Concept tested: iBGP split-horizon and Route Reflectors

Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/configuration/15-mt/irg-15-mt-book/irg-route-reflector.html

Topics

#BGP#iBGP#Route Reflector#BGP Split Horizon

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