Which of the following about a single-homed AS is FALSE?

Question

Options

• AA single-homed AS is also known as a stub AS.
• BA single-homed AS is also known as a leaf AS.
• CA single-homed AS uses either the ISP AS number or a private AS number.
• DA single-homed AS can be either transit or non-transit

• C
  4% (1)
• D
  96% (24)

Explanation

D is false because a single-homed AS, by definition, connects to only one upstream ISP - making it impossible to carry transit traffic between two other networks. Transit requires at least two separate connections to different external networks, so a single-homed AS is always non-transit.

Options A and B are both true: "stub AS" and "leaf AS" are standard synonyms for single-homed AS, referring to the fact that it sits at the edge of the internet topology with no downstream customers routing through it. Option C is also true: because a single-homed AS doesn't need a globally unique public AS number (it won't appear in BGP routing tables beyond its ISP), it can borrow the ISP's AS number or use a private AS number (64512–65535).

Memory tip: Picture a dead-end street - you can enter and exit, but no one drives through it to reach somewhere else. Single-homed = one connection = dead end = non-transit, always.

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