What is the size of a point-to-point GRE header, and what is the protocol number at the IP layer?
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A. B. C. D. E.B.
The correct answer is B. 4 bytes, and protocol number 47.
Generic Routing Encapsulation (GRE) is a protocol used to encapsulate one protocol inside another protocol. It is used in many scenarios, including creating virtual private networks ( VPNs) and connecting remote sites.
The GRE header consists of 4 bytes, and it is added between the IP header and the payload. The GRE header contains fields such as a version number, a protocol type, a checksum, and a key field.
The protocol number at the IP layer for GRE is 47. This is a protocol number assigned by the Internet Assigned Numbers Authority (IANA) for GRE.
Option A, which states that the GRE header is 8 bytes and the protocol number is 74, is incorrect. There is no protocol number 74 assigned for GRE.
Option C, which states that the GRE header is 2 bytes and the protocol number is 71, is incorrect. The GRE header is larger than 2 bytes, and there is no protocol number 71 assigned for GRE.
Option D, which states that the GRE header is 24 bytes and the protocol number is 1, is incorrect. The GRE header is smaller than 24 bytes, and protocol number 1 is assigned for the Internet Control Message Protocol (ICMP).
Option E, which states that the GRE header is 8 bytes and the protocol number is 47, is incorrect. The correct size for the GRE header is 4 bytes, not 8 bytes.