HP-UX Reference (11i v2 07/12) - 7 Device (Special) Files, 9 General Information, Index (vol 10)

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IP(7P) IP(7P)

IP_DROP_MEMBERSHIP

allows the system to leave a multicast group. 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_DROP_MEMBERSHIP, &mreq, sizeof(mreq));

The system remains a member of the multicast group until the last socket that joined the group is closed or

has dropped membership in the group.

IP_MULTICAST_IF

speciﬁes a local network interface to be used when sending multicast datagrams

through this socket. For example:

#include <arpa/inet.h>

struct in_addr addr;

addr.s_addr = inet_addr("192.1.2.3");

setsockopt(s, IPPROTO_IP, IP_MULTICAST_IF, &addr, sizeof(addr));

Normally, applications do not need to specify the interface. By default, multicast datagrams are sent from

the interface speciﬁed by the routing conﬁguration, namely the interface associated with the speciﬁc multi-

cast group, with the default multicast route or with the default route. If addr is set to the address

INADDR_ANY , the default interface is selected. Otherwise, addr should be the IP address of a local inter-

face.

IP_MULTICAST_LOOP

enables or disables loopback for multicast datagrams sent through this socket.

For example:

unsigned char loop = 1;

setsockopt(s, IPPROTO_IP, IP_MULTICAST_LOOP, &loop, sizeof(loop));

Note that the type of the optval parameter is unsigned char instead of int, which is common for

boolean socket options. This option is provided for compatibility only. Normally, if a multicast datagram is

sent to a group that the system has joined, a copy of the datagram is always looped back and delivered to

any applications that are bound to the destination port. See DEPENDENCIES below.

IP_MULTICAST_TTL

controls the scope a multicast by setting the time-to-live value for multicast

datagrams sent through this socket. For example:

unsigned char ttl = 64;

setsockopt(s, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl));

Note that the type of optval parameter is unsigned char instead int, which is common for socket

options. By default, the time-to-live ﬁeld (TTL) is one, which limits the multicast to the local network. If

the TTL is zero, the multicast is limited to the local system (loopback). If the TTL is two, the multicast can

be forwarded through at most one gateway; and so forth. Multicast datagrams can be forwarded to other

networks only if there are special multicast routers on the local and intermediate networks.

DEPENDENCIES

The behavior of IP_MULTICAST_LOOP

depends on the network driver and interface card. Normally,

loopback cannot be disabled, even if

IP_MULTICAST_LOOP

is set to zero, because it occurs in the driver

or in the network interface. However, if the outbound interface is

lo0 (127.0.0.1), or if

IP_MULTICAST_TTL is set to zero, setting IP_MULTICAST_LOOP

to zero will disable loopback for

multicast datagrams sent through the socket.

ERRORS

One of the following errors may be returned if a call to

setsockopt() or getsockopt() fails.

[EADDRINUSE] The speciﬁed multicast group has been joined already on socket.

[EADDRNOTAVAIL] The speciﬁed IP address is not a local interface address; or there is no route

for the speciﬁed multicast address; or the speciﬁed multicast group has not

been joined.

[EINVAL] The parameter level is not IPPROTO_IP ;oroptval is the NULL address; or

the speciﬁed multicast address is not valid.

[ENOBUFS] Insufﬁcient memory is available for internal system data structures.

[ENOPROTOOPT] The parameter optname is not a valid socket option for the IPPROTO_IP

level.

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