Final answer:
The fields in an IPv4 datagram header include Version, Header Length, Type of Service, Total Length, Identification, Flags, Fragment Offset, Time to Live, Protocol, Header Checksum, Source Address, Destination Address, Optional Options, and Padding. They provide necessary information for data packet delivery.
Step-by-step explanation:
The fields in an IPv4 datagram header ensure the correct delivery of data across an IP network. Each IPv4 datagram has a header that contains the following fields:
- Version - Indicates the version of IP (4 for IPv4).
- Header Length (IHL) - Specifies the header's length in 32-bit words.
- Type of Service (ToS) - Designed to indicate the quality of service desired, deprecated now in favor of Differentiated Services (DiffServ).
- Total Length - Specifies the total length of the datagram, header and data included.
- Identification - A unique identifier for the datagram.
- Flags - Control and identification flags.
- Fragment Offset - Indicates where in the datagram this fragment belongs.
- Time to Live (TTL) - Limits the datagram's lifetime to prevent it from looping indefinitely.
- Protocol - Indicates the next level protocol used in the data portion of the datagram.
- Header Checksum - Used for error-checking of the header.
- Source Address - The IPv4 address of the sender of the datagram.
- Destination Address - The IPv4 address of the receiver of the datagram.
- Options (Optional) - Allows for extra functionalities; not often used.
- Padding (Variable) - Ensures the header is a multiple of 32 bits.
These fields are crucial for the routing and delivery of data packets across various networks until they reach their intended destination.