#include "include/jipsa.h"
Detailed Description
Internet Protocol (IP) Security Association
See https://en.wikipedia.org/wiki/Internet_Protocol
The Internet Protocol (IP) is the principal communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet.
IP has the task of delivering packets from the source host to the destination host solely based on the IP addresses in the packet headers. For this purpose, IP defines packet structures that encapsulate the data to be delivered. It also defines addressing methods that are used to label the datagram with source and destination information.
Historically, IP was the connectionless datagram service in the original Transmission Control Program introduced by Vint Cerf and Bob Kahn in 1974; the other being the connection-oriented Transmission Control Protocol (TCP). The Internet protocol suite is therefore often referred to as TCP/IP.
The first major version of IP, Internet Protocol Version 4 (IPv4), is the dominant protocol of the Internet. Its successor is Internet Protocol V6
The header for IPv4 is configured as follows (See RFC 791) [1]
Version: 4 bits
The Version field indicates the format of the internet header
IHL: 4 bits
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.
Type of Service: 8 bits
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.
The use of the Delay, Throughput, and Reliability indications may increase the cost (in some sense) of the service. In many networks better performance for one of these parameters is coupled with worse performance on another. Except for very unusual cases at most two of these three indications should be set.
The type of service is used to specify the treatment of the datagram during its transmission through the internet system. Example mappings of the internet type of service to the actual service provided on networks such as AUTODIN II, ARPANET, SATNET, and PRNET is given in "Service Mappings"
The Network Control precedence designation is intended to be used within a network only. The actual use and control of that designation is up to each network. The Internetwork Control designation is intended for use by gateway control originators only. If the actual use of these precedence designations is of concern to a particular network, it is the responsibility of that network to control the access to, and use of, those precedence designations.
Total Length: 16 bits
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. Such long datagrams are impractical for most hosts and networks. All hosts must be prepared to accept datagrams of up to 576 octets (whether they arrive whole or in fragments). It is recommended that hosts only send datagrams larger than 576 octets if they have assurance that the destination is prepared to accept the larger datagrams.
The number 576 is selected to allow a reasonable sized data block to be transmitted in addition to the required header information. For example, this size allows a data block of 512 octets plus 64 header octets to fit in a datagram. The maximal internet header is 60 octets, and a typical internet header is 20 octets, allowing a margin for headers of higher level protocols.
Identification: 16 bits
An identifying value assigned by the sender to aid in assembling the fragments of a datagram.
Flags: 3 bits
Various Control Flags Bit 0: reserved, must be zero Bit 1: (DF) 0 = May Fragment, 1 = Don’t Fragment Bit 2: (MF) 0 = Last Fragment, 1 = More Fragments
Fragment Offset: 13 bits
This field indicates where in the datagram this fragment belongs The fragment offset is measured in units of 8 octets (64 bits). The first fragment has offset zero.
Time to Live: 8 bits
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.
Protocol: 8 bits
This field indicates the next level protocol used in the data portion of the internet datagram. The values for various protocols are specified in "Assigned Numbers"
Header Checksum: 16 bits
A checksum on 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.
This is a simple to compute checksum and experimental evidence indicates it is adequate, but it is provisional and may be replaced by a CRC procedure, depending on further experience.
Source Address: 32 bits
The source address. See section 3.2.
Destination Address: 32 bits
The destination address. See section 3.2.
The header for IPv6 is configured as follows (see RFC 2460) [2]
Version:
4-bit Internet Protocol version number = 6.
Traffic Class:
8-bit traffic class field. See section 7.
Flow Label:
20-bit flow label. See section 6.
Payload Length:
16-bit unsigned integer. Length of the IPv6 payload, i.e., the rest of the packet following this IPv6 header, in octets. (Note that any extension headers present are considered part of the payload, i.e., included in the length count.)
Next Header:
8-bit selector. Identifies the type of header immediately following the IPv6 header. Uses the same values as the IPv4 Protocol field [RFC-1700 et seq.]
Hop Limit:
8-bit unsigned integer. Decremented by 1 by each node that forwards the packet. The packet is discarded if Hop Limit is decremented to zero.
Source Address:
128-bit address of the originator of the packet
Destination Address:
128-bit address of the intended recipient of the packet (possibly not the ultimate recipient, if a Routing header is present)
IPv4 vs IPv6 Header Comparison [3]
For API Documentation:
- See also
- ProtocolPP::jsecass
- ProtocolPP::jprotocol
- ProtocolPP::jip
- ProtocolPP::jipsa
- ProtocolPP::jicmp
- ProtocolPP::jarray
- ProtocolPP::jenum
For Additional Documentation:
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The documentation for this class was generated from the following file:
- include/jipsa.h
