Description of Ipv4 Header Fields

Topics: Domain Name System, IPv4, Routing protocol Pages: 4 (1582 words) Published: November 13, 2005
For the first section of this Mid Term, I will describe the fields in the IP version 4 (IPv4) packet header. (What is the structure (each field) of an IPv4 packet?). The first field is a 4-bit version field. Next we have a 4-bit Internet Header Length (IHL) that tells the number of 32-bit words in the IPv4 header. The next field is an 8-bit Type of Service (ToS) field. This technology was never fully implemented so new technology has been developed to utilize this portion of the header. It now relays the DiffServ and Explicit Congestion Notification (ECN) to help the reliability of real time data streaming technologies. The Total Length filed is next. This is a 16-bit field that shows the entire datagram size including header and data, in 8-bit bytes. Next we have a 16-bit Identification field. This field is used primarily to uniquely identify fragment of an original IP datagram. A 3-bit field to control or identify fragments is next. This field must either be zero for reserved, don't fragment, and more fragments. The fragment offset field in next and is a 13-bit field used to determine the particular place of a fragment in the original IP datagram. The 8-bit Time to Live (TTL) field follows. This field stops a datagram from going in circles on a network. It used to be measured in seconds, but is now a hop count field. Once the field comes to zero after passing each switch or router, the packet is no longer forwarded. The 8-bit protocol field follows to show the protocol used in the data portion of the datagram. There are predestinated values for different protocols such as ICMP (1), TCP (6), and UDP (17). Next is the 16-bit header Checksum field. Since some values in an IPv4 header may change, the checksum must be adjusted through the network. Following the checksum field there is a 32-bit Source address field directly followed by another 32-bit Destination address field. Finally, before the data, there can also be additional header fields...
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