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)