Which of the following parameters does NOT have to match for an iBGP session to be successfully established?

Question

Options

• ABGP version number.
• BThe local AS number.
• CThe Hold Time.
• DAuthentication.

• B
  3% (1)
• C
  94% (29)
• D
  3% (1)

Explanation

Hold Time is a negotiated parameter, not a matched one - during the BGP OPEN message exchange, each peer advertises its own Hold Time value, and the lower of the two is automatically selected for the session. This means two peers can have different configured Hold Times and still form a successful iBGP session.

Why the distractors are wrong:

• A (BGP version): Both peers must agree on the same BGP version (version 4 in practice); a mismatch causes a NOTIFICATION error and the session fails.
• B (Local AS number): For iBGP specifically, both routers must belong to the same AS - if the AS number in the OPEN message doesn't match what the peer expects, the session is rejected.
• D (Authentication): If MD5 authentication is configured on one peer, it must be configured with the identical key on the other; any mismatch prevents TCP session establishment entirely.

Memory tip: Remember "Hold Time = Haggling" - BGP peers haggle down to the lowest offered value, so they don't need to agree in advance. Everything else (version, AS, auth) is a hard requirement where both sides must be identical.

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