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350-501 · Question #103

Refer to the exhibit. R1 and R2 are directly connected and IS-IS routing has been enabled between R1 and R2 R1 message periodically Based on this output, which statement is true?

The correct answer is C. IS-IS neighbor authentication is failing for Level 1 PDUs only. Based on the provided output, the IS-IS neighbor authentication is specifically failing for Level 1 Protocol Data Units (PDUs), indicating a mismatch in Level 1 authentication settings.

Networking

Question

Refer to the exhibit. R1 and R2 are directly connected and IS-IS routing has been enabled between R1 and R2 R1 message periodically Based on this output, which statement is true?

Exhibit

350-501 question #103 exhibit

Options

  • AIS-IS neighbor authentication is failing for Level 2 first and then for Level 1 PDUs
  • B1S-1S neighbor authentication is failing for Level 1 and Level 2 PDUs .
  • CIS-IS neighbor authentication is failing for Level 1 PDUs only
  • DIS-IS neighbor authentication is failing for Level 2 PDUs only.

How the community answered

(26 responses)
  • A
    4% (1)
  • B
    8% (2)
  • C
    85% (22)
  • D
    4% (1)

Why each option

Based on the provided output, the IS-IS neighbor authentication is specifically failing for Level 1 Protocol Data Units (PDUs), indicating a mismatch in Level 1 authentication settings.

AIS-IS neighbor authentication is failing for Level 2 first and then for Level 1 PDUs

This statement would be true only if Level 2 authentication errors were present and occurred before Level 1 errors in the output, which is not indicated.

B1S-1S neighbor authentication is failing for Level 1 and Level 2 PDUs .

This statement would be true if both Level 1 and Level 2 authentication errors were present in the output.

CIS-IS neighbor authentication is failing for Level 1 PDUs onlyCorrect

If the debug output or log messages explicitly show 'IS-IS: L1AUTH-ERR' and no 'IS-IS: L2AUTH-ERR' messages, it indicates that only Level 1 IS-IS PDUs are experiencing authentication failures. This typically means the Level 1 authentication keys or methods do not match between the neighbors.

DIS-IS neighbor authentication is failing for Level 2 PDUs only.

This statement would be true only if Level 2 authentication errors were present and Level 1 errors were absent in the output.

Concept tested: IS-IS authentication error interpretation

Source: https://www.cisco.com/c/en/us/support/docs/ip/integrated-intermediate-system-to-intermediate-system-is-is/13309-isis-debug.html

Topics

#IS-IS#Routing Protocol Authentication#IS-IS Levels

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