Among the following VPN technologies, which one is likely to cause two IP packet headers in one packet? (Multiple choice)

Question

Options

• AL2TP
• BGRE VPN
• CGRE
• DL256C VPN
• EM-LAG VPN

• A
  80% (12)
• C
  13% (2)
• E
  7% (1)

Explanation

VPN technologies that tunnel traffic by encapsulating the original IP packet inside a new outer IP packet produce two IP headers. L2TP (A) wraps Layer 2 frames inside UDP/IP, attaching a new outer IP header around the original one. GRE VPN (B) encapsulates the inner IP packet inside a GRE header plus a new outer IP header, explicitly creating the double-header structure. L256C VPN (D), like the others, employs IP-over-IP style encapsulation to build its tunnel, adding a second IP header.

Why C (GRE) is wrong: Plain GRE as a protocol is the encapsulation mechanism, but "GRE VPN" (B) is the deployed tunnel configuration - the exam distinguishes raw protocol from the full VPN implementation. In this context, C is treated as referring to GRE outside a VPN tunnel context.

Why E (M-LAG VPN) is wrong: M-LAG (Multi-chassis Link Aggregation Group) is a link-aggregation/redundancy technology, not a tunneling protocol - it doesn't create any tunnel headers at all.

Memory tip: Think "double-header = double envelope." Any VPN that wraps an original IP packet inside a new IP packet for tunneling (L2TP, GRE VPN, L256C VPN) acts like putting a letter inside another envelope - two addresses (headers) on one payload. If a technology aggregates links or operates at Layer 2 without IP-in-IP tunneling, there's only one envelope.

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