What is the protocol number for Generic Routing Encapsulation (GRE)?

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Multiple Choice

What is the protocol number for Generic Routing Encapsulation (GRE)?

Explanation:
The key idea is that the IP header uses a protocol field to identify what kind of payload is inside. GRE is signaled by the protocol number 47, so the packet is treated as a GRE-encapsulated frame that will be processed to decapsulate or route the inner payload. In practice, GRE wraps other network-layer protocols inside an IP tunnel, which is common in VPN setups. The other numbers simply correspond to different, non-GRE protocols, so they wouldn’t indicate GRE.

The key idea is that the IP header uses a protocol field to identify what kind of payload is inside. GRE is signaled by the protocol number 47, so the packet is treated as a GRE-encapsulated frame that will be processed to decapsulate or route the inner payload. In practice, GRE wraps other network-layer protocols inside an IP tunnel, which is common in VPN setups. The other numbers simply correspond to different, non-GRE protocols, so they wouldn’t indicate GRE.

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