IP(4)

NAME
ip - Internet Protocol

SYNOPSIS
#include <sys/socket.h>
#include <netinet/in.h>

s = socket(AF_INET, SOCK_RAW, proto);

DESCRIPTION
IP is the transport layer protocol used by the Internet protocol family. Options may be set at the IP level when using higher-level protocols that are based on IP (such as TCP and UDP). It may also be accessed through a “raw socket” when developing new protocols, or special purpose applications.

A single generic option is supported at the IP level, IP_OPTIONS, that may be used to provide IP options to be transmitted in the IP header of each outgoing packet. Options are set with setsockopt(2) and examined with getsockopt(2). The format of IP options to be sent is that specified by the IP protocol specification, with one exception: the list of addresses for Source Route options must include the first-hop gateway at the beginning of the list of gateways. The first-hop gateway address will be extracted from the option list and the size adjusted accordingly before use. IP options may be used with any socket type in the Internet family.

Raw IP sockets are connectionless, and are normally used with the sendto and recvfrom calls, though the connect(2) call may also be used to fix the destination for future packets (in which case the read(2) or recv(2) and write(2) or send(2) system calls may be used).

If proto is 0, the default protocol IPPROTO_RAW is used for outgoing packets, and only incoming packets destined for that protocol are received. If proto is non-zero, that protocol number will be used on outgoing packets and to filter incoming packets.

Outgoing packets automatically have an IP header prepended to them (based on the destination address and the protocol number the socket is created with). Incoming packets are received with IP header and options intact.

DIAGNOSTICS
A socket operation may fail with one of the following errors returned:

[EISCONN]
    when trying to establish a connection on a socket which already has one, or when trying to send a datagram with the destination address specified and the socket is already connected;

[ENOTCONN]
    when trying to send a datagram, but no destination address is specified, and the socket hasn't been connected;

[ENOBUFS]
    when the system runs out of memory for an internal data structure;

[EADDRNOTAVAIL]
    when an attempt is made to create a socket with a network address for which no network interface exists.

The following errors specific to IP may occur when setting or getting IP options:

[EINVAL]
    An unknown socket option name was given.

[EINVAL]
    The IP option field was improperly formed; an option field was shorter than the minimum value or longer than the option buffer provided.

SEE ALSO
getsockopt(2), send(2), recv(2), intro(4), icmp(4), inet(4)