Why is ICMP used for tunneling?

• A. It provides high bandwidth.
• B. It is completely secure.
• C. It bypasses NAT.
• D. It is trusted and often allowed through firewalls.

Answer: (D)

ICMP tunneling works because ICMP is typically treated as trusted diagnostic traffic and is often permitted through firewalls. Since many networks allow ICMP echo requests/replies for ping and traceroute, data carried inside ICMP payloads can traverse devices that would block other protocols. This permissive handling makes ICMP a convenient carrier for a covert channel. It’s not about high bandwidth or security, and NAT behavior isn’t guaranteed, but the enduring reason it’s used for tunneling is that ICMP is commonly allowed through security devices.