Header size of the ICMP message is 8-bytes

ICMP (Internet Control Message Protocol) is a network protocol used for error reporting, diagnostic, and informational purposes in IP networks. It is primarily used by network devices to communicate error messages, such as unreachable hosts or network congestion, back to the source IP address.

The ICMP message consists of two parts: the ICMP header and the ICMP data. The ICMP header contains essential information about the message, while the ICMP data carries additional details or payload.

Let's explore the header size of the ICMP message:

1. ICMP Header
The ICMP header has a fixed size of 8 bytes (64 bits). It includes the following fields:

- Type (8 bits): Specifies the type of ICMP message, such as echo request (ping), echo reply, destination unreachable, time exceeded, etc.
- Code (8 bits): Further categorizes the ICMP message type. For example, for the destination unreachable type, the code field specifies the reason for the unreachable destination.
- Checksum (16 bits): A checksum is used to detect errors in the ICMP message header and data.
- Rest of Header (32 bits): Reserved for future use and should be set to zero.

2. ICMP Data
The ICMP data field varies in size depending on the ICMP message type. It carries additional information related to the specific ICMP message. For example, in an echo request (ping) message, the data may include a payload that is sent to the destination and returned in the echo reply message.

Summary
In summary, the header size of the ICMP message is 8 bytes (64 bits). The ICMP header contains the type, code, checksum, and reserved fields, while the ICMP data carries additional information specific to the ICMP message type.

Note: It's important to note that the total size of the ICMP message, including both the header and data, may vary depending on the specific ICMP message type and the payload it carries.