Which of the following descriptions about GRE is incorrect?

Question

Options

• AGRE supports simple keyword verification
• BGRE does not support multicasting and retransmission
• CGRE does not support authentication
• DGRE is a three-layer packaging technology

• A
  17% (7)
• B
  71% (29)
• C
  7% (3)
• D
  5% (2)

Explanation

Option B is the incorrect statement because GRE does support multicasting - encapsulating multicast packets is one of GRE's defining advantages over protocols like IPsec, and it's why GRE tunnels are commonly paired with dynamic routing protocols (OSPF, EIGRP) that rely on multicast. The "no retransmission" half of B is technically true but irrelevant, since the multicast claim makes the whole statement wrong.

• A is correct: GRE includes an optional Key field that provides simple keyword-based verification of tunnel endpoints.
• C is correct: GRE offers no built-in authentication or encryption; for security, it must be combined with IPsec.
• D is correct: GRE operates at Layer 3, adding an outer IP header to encapsulate the original packet - that's the "three-layer packaging" description.

Memory tip: Remember GRE by what it gives and what it lacks - it gives multicast support and Layer 3 encapsulation, but lacks security (no auth, no encryption). If an answer says GRE can't do multicasting, that's your red flag.

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