IP(4)                       BSD Programmer's Manual                      IP(4)

NAME
     ip - Internet Protocol

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

     int
     socket(AFINET, SOCKRAW, 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 applica-
     tions.

     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 speci-
     fied 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 re-
     ceived.  If proto is non-zero, that protocol number will be used on out-
     going 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 al-
                      ready connected;

     [ENOTCONN]       when trying to send a datagram, but no destination ad-
                      dress is specified, and the socket hasn't been connect-
                      ed;

     [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 net-
                      work 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)

HISTORY
     The ip protocol appeared in 4.2BSD.

4.2 Berkeley Distribution       March 27, 1993                               2