Understanding IPv4 Packet Header Fields: Key Facts for Computer Scientists

Which statement is correct about IPv4 packet header fields?

There are several correct statements about IPv4 packet header fields. Here are some key facts:

1. Total length: This field specifies the length (in bytes) of the entire IPv4 packet, including both the header and the payload. The maximum size is 65,535 bytes.

2. Identification: This field is used to uniquely identify fragments of an original IP packet that has been divided into smaller fragments for transmission. When an IP packet is fragmented, each fragment is assigned the same identification value.

3. Time to Live (TTL): This field indicates the maximum number of hops (routers) that a packet can pass through before being discarded. The TTL value is initially set by the sender and is typically decremented by one at each hop. If the TTL reaches zero, the packet is discarded.

4. Protocol: This field identifies the protocol used in the data portion of the IP packet. It is used by the receiving system to determine how to process the packet payload. For example, a value of 6 corresponds to the TCP protocol, while a value of 17 corresponds to the UDP protocol.

5. Source and Destination IP addresses: These fields contain the source and destination IP addresses of the packet. They identify the sending and receiving devices on the network.

6. Header Checksum: This field is used to check the integrity of the header. It is computed by performing a checksum calculation over the header contents and is used by the receiving system to verify that the header has not been corrupted during transmission.

It is important to note that IPv4 packet headers have more fields, and their positions and sizes are fixed. These fields play a critical role in the delivery and processing of IP packets across networks.

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