The (*, G) routing table entry in multicast routing can guide packet forwarding.

Question

Options

• ATRUE
• BFALSE
• C
• D

• A
  5% (1)
• B
  77% (17)
• C
  5% (1)
• D
  14% (3)

Explanation

Option B is correct because the (, G) entry uses a wildcard () in place of a specific source address, which means it lacks the precise source information required for Reverse Path Forwarding (RPF) checks - the core mechanism multicast routers use to select the correct incoming interface and prevent routing loops. Actual per-packet multicast forwarding relies on (S, G) entries, which pair a known source S with group G, giving the router everything it needs to make a definitive forwarding decision. The (, G) entry plays a role in shared-tree construction and group membership state, but it is the (S, G) state that drives the forwarding plane. Option A (TRUE) is wrong because treating (, G) as a forwarding entry would make RPF ambiguous - without knowing S, you cannot confirm which interface a packet legitimately arrived on.

Memory tip: Think of it as a GPS analogy - (*, G) is like knowing your destination city but not your starting point; you can't plot a route (forward a packet) until you also know the source (S, G).

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