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350-501 · Question #78

Refer to the exhibit. Assume all other configurations are correct and the network is otherwise operating normally. Which conclusion can you draw about the neighbor relationship between routers R1 and

The correct answer is B. The neighbor relationship is down because R1 believes R2 is in AS 65012.. The BGP neighbor relationship between R1 and R2 is down because R1's configuration expects R2 to be in AS 65012, but R2 is actually configured with AS 65112 as its local AS.

Networking

Question

Refer to the exhibit. Assume all other configurations are correct and the network is otherwise operating normally. Which conclusion can you draw about the neighbor relationship between routers R1 and R2?

Exhibit

350-501 question #78 exhibit

Options

  • AThe neighbor relationship will be up only if the two devices have activated the correct neighbor
  • BThe neighbor relationship is down because R1 believes R2 is in AS 65012.
  • CThe neighbor relationship is up
  • DThe neighbor relationship is down because the loco I-as value for R2 is missing in the R1

How the community answered

(40 responses)
  • A
    10% (4)
  • B
    85% (34)
  • C
    3% (1)
  • D
    3% (1)

Why each option

The BGP neighbor relationship between R1 and R2 is down because R1's configuration expects R2 to be in AS 65012, but R2 is actually configured with AS 65112 as its local AS.

AThe neighbor relationship will be up only if the two devices have activated the correct neighbor

The exhibit provides specific information about an AS mismatch, which is a definite reason for the neighbor relationship to be down, making this a general and less specific statement.

BThe neighbor relationship is down because R1 believes R2 is in AS 65012.Correct

The "neighbor 192.168.1.2 remote-as 65012" command on R1 indicates that R1 expects peer 192.168.1.2 (R2) to be in AS 65012. The exhibit for R2 shows "local-as 65112", meaning R2 identifies itself as AS 65112 to external peers, causing an AS mismatch and preventing the BGP session from establishing.

CThe neighbor relationship is up

The neighbor relationship is down due to an AS mismatch between R1's expectation and R2's actual AS configuration.

DThe neighbor relationship is down because the loco I-as value for R2 is missing in the R1

The term "loco I-as" is not standard, and the exhibit clearly shows the "local-as" configured on R2, which is present and correctly configured on R2 but mismatches R1's remote AS configuration.

Concept tested: BGP AS mismatch

Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/configuration/xe-3s/asr1000/bgp-xe-3s-asr1000-book/bgp-conf-xe.html

Topics

#BGP#Neighbor Relationship#AS Mismatch#Troubleshooting

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