ip_header Struct Reference
[Internet Protocol (IP) Service]

Internet header. More...

#include <ip_header.h>

Data Fields

uint8_t header_length:4
 Internet Header Length is the length of the internet header in 32~bit words, and thus points to the beginning of the data.
uint8_t version:4
 The Version field indicates the format of the internet header.
uint8_t tos
 The Type of Service provides an indication of the abstract parameters of the quality of service desired.
uint16_t total_length
 Total Length is the length of the datagram, measured in octets, including internet header and data.
uint16_t identification
 An identifying value assigned by the sender to aid in assembling the fragments of a~datagram.
uint8_t fragment_offset_high:5
 This field indicates where in the datagram this fragment belongs.
uint8_t flags:3
 Various control flags.
uint8_t fragment_offset_low
 This field indicates where in the datagram this fragment belongs.
uint8_t ttl
 This field indicates the maximum time the datagram is allowed to remain in the internet system.
uint8_t protocol
 This field indicates the next level protocol used in the data portion of the internet datagram.
uint16_t header_checksum
 A checksum of the header only.
uint32_t source_address
 The source address.
uint32_t destination_address
 The destination address.

Detailed Description

Internet header.

The variable options should be included after the header itself and indicated by the increased header length value.


Field Documentation

The destination address.

Referenced by ip_deliver_local(), ip_get_destination(), and ip_prepare_packet().

This field indicates where in the datagram this fragment belongs.

High bits.

Referenced by ip_fragment_packet_data(), and ip_prepare_packet().

This field indicates where in the datagram this fragment belongs.

Low bits.

Referenced by ip_fragment_packet_data(), and ip_prepare_packet().

A checksum of the header only.

Since some header fields change (e.g., time to live), this is recomputed and verified at each point that the internet header is processed. The checksum algorithm is: The checksum field is the 16~bit one's complement of the one's complement sum of all 16~bit words in the header. For purposes of computing the checksum, the value of the checksum field is zero.

Referenced by ip_create_last_header(), ip_fragment_packet(), ip_fragment_packet_data(), ip_prepare_packet(), and ip_process_packet().

Internet Header Length is the length of the internet header in 32~bit words, and thus points to the beginning of the data.

Note that the minimum value for a~correct header is~5.

Referenced by ip_create_last_header().

An identifying value assigned by the sender to aid in assembling the fragments of a~datagram.

Referenced by ip_prepare_packet().

This field indicates the next level protocol used in the data portion of the internet datagram.

Referenced by ip_deliver_local(), and ip_prepare_icmp().

The source address.

Referenced by ip_deliver_local(), ip_prepare_icmp(), and ip_prepare_packet().

uint8_t ip_header::tos

The Type of Service provides an indication of the abstract parameters of the quality of service desired.

These parameters are to be used to guide the selection of the actual service parameters when transmitting a~datagram through a~particular network. Several networks offer service precedence, which somehow treats high precedence traffic as more important than other traffic (generally by accepting only traffic above a~certain precedence at time of high load). The major choice is a~three way tradeoff between low-delay, high-reliability, and high-throughput.

Total Length is the length of the datagram, measured in octets, including internet header and data.

This field allows the length of a~datagram to be up to 65,535~octets.

Referenced by ip_fragment_packet_data(), and ip_prepare_packet().

uint8_t ip_header::ttl

This field indicates the maximum time the datagram is allowed to remain in the internet system.

If this field contains the value zero, then the datagram must be destroyed. This field is modified in internet header processing. The time is measured in units of seconds, but since every module that processes a~datagram must decrease the TTL by at least one even if it process the datagram in less than a~second, the TTL must be thought of only as an upper bound on the time a~datagram may exist. The intention is to cause undeliverable datagrams to be discarded, and to bound the maximum datagram lifetime.

Referenced by ip_process_packet().

The Version field indicates the format of the internet header.

Referenced by ip_deliver_local(), ip_prepare_icmp(), ip_prepare_packet(), and ip_process_packet().


The documentation for this struct was generated from the following file:

Generated on Thu Mar 11 20:48:28 2010 for Networking and TCP/IP stack for HelenOS system by  doxygen 1.6.1