HP-UX Reference (11i v1 05/09) - 7 Device (Special) Files, 9 General Information, Index (vol 10)

i
IP(7P) IP(7P)
NAME
IP - Internet Protocol
SYNOPSIS
#include <sys/socket.h>
#include <netinet/in.h>
s = socket(AF_INET, SOCK_DGRAM, 0);
DESCRIPTION
IP is the network-layer protocol used by the Internet protocol family. It encapsulates TCP and UDP mes-
sages into datagrams to be transmitted by the network interface. Normally, applications do not need to
interface directly to IP. However, certain multicast socket options are controlled by passing options to the
IPPROTO_IP protocol level through a UDP socket, and IP Type of Service is controlled by passing an
option to the IPPROTO_IP protocol level through either a TCP or UDP socket. (See the getsockopt(2)
manual page.)
The following socket options are defined in the include file <
netinet/in.h >. The type of the variable
pointed to by the optval parameter is indicated in parentheses. The data types
struct ip_mreq and
struct in_addr are defined in <netinet/in.h >.
IP_TOS (unsigned int) Sets the IP Type of Service. Allowable values for optval
are 4 for high reliability, 8 for high throughput, and 16 for low delay.
Other values will not return an error, but may have unpredictable results.
Default: zero.
IP_ADD_MEMBERSHIP
(struct ip_mreq) Requests that the system join a multicast group.
IP_DROP_MEMBERSHIP
(struct ip_mreq) Allows the system to leave a multicast group.
IP_MULTICAST_IF (struct in_addr
) Specifies a network interface other than the default
to be used when sending multicast datagrams through this socket. Default:
multicast datagrams are sent from the interface associated with the specific
multicast group, with the default multicast route or with the default route.
IP_MULTICAST_LOOP
(unsigned char; boolean) Enables or disables loopback in the IP layer
for multicast datagrams sent through this socket. The value of the variable
pointed to by optval is zero (disable) or non-zero (enable). This option is
provided for compatibility only. Normally, multicast datagrams are always
looped back if the system has joined the group. See DEPENDENCIES
below. Default: enabled.
IP_MULTICAST_TTL
(unsigned char) Specifies the time-to-live value for multicast datagrams
sent through this socket. The value of the variable pointed to by optval can
be zero through 255. Default: one.
IP_ADD_MEMBERSHIP
requests that the system join a multicast group on the specified interface. For
example:
struct ip_mreq mreq;
mreq.imr_multiaddr.s_addr = net_addr("224.1.2.3");
mreq.imr_interface.s_addr = INADDR_ANY;
setsockopt(s, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq));
A system must join a group on an interface in order to receive multicast datagrams sent on the network to
which that interface connects. If imr_interface is set to INADDR_ANY, the system joins the specified
group on the interface that datagrams for that group would be sent from, based the routing configuration.
Otherwise, imr_interface should be the IP address of a local interface. An application can join up to
IP_MAX_MEMBERSHIPS multicast groups on each socket. IP_MAX_MEMBERSHIPS is defined in
<netinet/in.h >. However, each network interface may impose a smaller system-wide limit because of
interface resource limitations and because the system uses some link-layer multicast addresses.
The application must also bind to the destination port number in order to receive datagrams that are sent
to that port number. If the application binds to the address INADDR_ANY, it may receive all datagrams
that are sent to the port number. If the application binds to a multicast group address, it may receive only
datagrams sent to that group and port number. It is not necessary to join a multicast group in order to
send datagrams to it.
HP-UX 11i Version 1: September 2005 − 1 − Hewlett-Packard Company Section 7−−49