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HP OpenVMS systems documentation |
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The netent structure, defined in the NETDB.H header file, holds a network name, a list of aliases associated with the network, and the network's number specified as an internet address from the network database.
The netent structure definition is as follows:
struct netent {
char *n_name; /* official name of net */
char **n_aliases; /* alias list */
int n_addrtype; /* net address type */
long n_net; /* net number */
};
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The netent structure members are as follows:
The protoent structure, defined in the NETDB.H header file, holds the description of the protocol from the protocols table.
A protocol is described by the protoent structure, as follows:
struct protoent {
char *p_name; /* official name of protocol */
char **p_aliases; /* alias list */
long p_proto; /* protocol number */
};
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The members of this structure are:
| p_name | The official name of the protocol. |
| p_aliases | A zero-terminated list of alternate names for the protocol. |
| p_proto | The protocol number. |
The servent structure, defined in the NETDB.H header file, specifies or obtains a service name, a list of aliases associated with the service, and the service's number specified as an Internet address from the services database. An entry in the services database is created with the following TCP/IP management command:
SET SERVICE service |
For more information, refer to the HP TCP/IP Services for OpenVMS Management Command Reference guide.
A service mapping is described by the servent structure, as follows:
struct servent {
char *s_name; /* official service name */
char **s_aliases; /* alias list */
int s_port; /* port number, network byte order */
char *s_proto; /* protocol to use */
};
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The servent structure members are as follows:
The
getservbyname()
function maps service names to a
servent
structure by specifying a service name and, optionally, a qualifying
protocol.
3.2.12 sockaddr Structure
The sockaddr structure, defined in the SOCKET.H header file, holds a general address family.
The SOCKET.H header file defines the following structures for BSD Versions 4.3 and 4.4:
The osockaddr structure definition for use with BSD Version 4.3 is as follows:
struct osockaddr {
u_short sa_family; /* address family */
char sa_data[14]; /* up to 14 bytes of direct address */
};
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The osockaddr structure members are as follows:
The sockaddr structure definition for use with BSD Version 4.4 is as follows:
struct sockaddr {
u_char sa_len; /* total length */
u_char sa_family; /* address family */
char sa_data[14]; /* up to 14 bytes of direct address */
};
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The sockaddr structure members are as follows:
The sockaddr_in structure, defined in the IN.H header file, specifies an internet address family.
The sockaddr_in structure definition is as follows:
struct sockaddr_in {
short sin_family; /* address family */
u_short sin_port; /* port number */
struct in_addr sin_addr; /* internet address */
char sin_zero[8]; /* 8-byte field of all zeroes */
};
|
The sockaddr_in structure members are as follows:
The sockaddr_in6 structure, defined in the IN6.H header file, defines an IPv6 socket address.
The IN6.H file defines the following structures depending on the setting of the _SOCKADDR_LEN compilation symbol:
If an application does not define the _SOCKADDR_LEN compilation symbol, the compiler generates the following BSD Version 4.3 structure:
struct sockaddr_in6 {
sa_family_t sin6_family; /* AF_INET6 */
in_port_t sin6_port; /* Transport layer port # */
uint32_t sin6_flowinfo; /* IPv6 flow information */
struct in6_addr sin6_addr; /* IPv6 address */
uint32_t sin6_scope_id; /* set of interfaces for a scope */
};
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The sockaddr_in6 structure members are as follows:
If an application defines the _SOCKADDR_LEN compilation symbol, the compiler generates the following BSD Version 4.4 structure.
struct sockaddr_in6 {
# define SIN6_LEN
uint8_t sin6_len; /* length of this struct */
sa_family_t sin6_family; /* AF_INET6 */
in_port_t sin6_port; /* Transport layer port # */
uint32_t sin6_flowinfo; /* IPv6 flow information */
struct in6_addr sin6_addr; /* IPv6 address */
uint32_t sin6_scope_id; /* set of interfaces for a scope */
};
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The sockaddr_in6 structure members are as follows:
The timeval structure, defined in the SOCKET.H header file, specifies time intervals. The timeval structure definition is as follows:
struct timeval {
long tv_sec;
long tv_usec;
};
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The timeval structure members are as follows:
You can include header files on a OpenVMS system using any one of the following preprocessor directive statements:
#include types #include <types.h> #include <sys/types.h> |
The #include types form of the #include preprocessor directive is possible on OpenVMS systems because all header files are located in a text library in the SYS$LIBRARY directory. On UNIX systems, you must specify header files (and subdirectories that locate a header file) within angle brackets (< >) or quotation marks (" ") .
For example, to include the header file TYPES.H on a UNIX system, use the following form of the #include directive:
#include <sys/types.h> |
Table 3-3 lists the constants and address variables available for use with the IPv6 structures.
| Entry | Description |
|---|---|
| in6addr_any | The wildcard address in network byte order for the structure in6_addr . |
| IN6ADDR_ANY_INIT | A symbolic constant used to initialize an in6_addr structure when it is declared. |
| in6addr_loopback | A loopback address defined in network byte order. |
| IN6ADDR_LOOPBACK_INIT | A symbolic constant used to initialize an in6_addr structure when it is declared. |
When TCP/IP Services initializes an interface, it assigns an integer known as an interface index to identify the interface. This interface identification is used to determine the interface on which a datagram is sent or received, or on which a multicast group is joined.
Table 3-4 lists the functions related to handling the interface identification.
| Function | Description |
|---|---|
| if_nametoindex() | Maps an interface name to its corresponding index. |
| if_indextoname() | Maps an interface index to its corresponding name. |
| if_nameindex() | Returns an array of all interface names and indexes. |
| if_freenameindex() | Frees dynamic memory allocated by if_nameindex() to the array of interface names and indexes. |
To send IPv6 multicast datagrams, an application indicates the multicast group to send to by specifying an IPv6 multicast address in a sendto() function. The system maps the specified IPv6 destination address to the appropriate Ethernet or FDDI multicast address prior to transmitting the datagram.
An application can explicitly control multicast options with arguments to the setsockopt() function. The following options can be set by an application using the setsockopt() function:
u_char hops;
hops=2;
if (setsockopt(sock, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &hops,
sizeof(hops)) < 0)
perror("setsockopt: IPV6_MULTICAST_HOPS error");
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u_int if_index = 1;
.
.
.
if (setsockopt(sock, IPPROTO_IPV6, IPV6_MULTICAST_IF, &if_index,
sizeof(if_index)) < 0)
perror ("setsockopt: IPV6_MULTICAST_IF error");
else
printf ("new interface set for sending multicast datagrams\n");
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u_char loop=0;
if (setsockopt( sock, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, &loop,
sizeof(loop)) < 0)
perror("setsockopt: IPV6_MULTICAST_LOOP error");
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Before a node can receive IPv6 multicast datagrams destined for a particular multicast group other than the All Nodes group, an application must direct the node to become a member of that multicast group.
This section describes how an application can direct a node to add itself to and remove itself from a multicast group.
An application can direct the node it is running on to join a multicast group by using the IPV6_JOIN_GROUP option to the setsockopt() function:
struct ipv6_mreq imr6;
.
.
.
imr6.ipv6mr_interface = if_index;
if (setsockopt( sock, IPPROTO_IPV6, IPV6_JOIN_GROUP,
(char *)&imr6, sizeof(imr6)) < 0)
perror("setsockopt: IPV6_JOIN_GROUP error");
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The imr6 parameter has the following structure:
structipv6_mreq {
struct in6_addr ipv6mr_multiaddr; /* IP multicast address of group */
unsigned int ipv6mr_interface; /* local interface index */
};
|
Each multicast group membership is associated with a particular interface. It is possible to join the same group on multiple interfaces. The ipv6mr_interface variable can be specified with a value of 0, which allows an application to choose the default multicast interface. Alternatively, specifying one of the host's local interfaces allows an application to select a particular multicast-capable interface. The maximum number of memberships that can be added on a single socket is subject to the IPV6_MAX_MEMBERSHIPS value, which is defined in the IN6.H header file.
To drop membership from a particular multicast group, use the IPV6_LEAVE_GROUP option to the setsockopt function:
struct ipv6_mreq imr6;
if (setsockopt( sock, IPPROTO_IPV6, IPV6_LEAVE_GROUP, &imr6,
sizeof(imr6)) < 0)
perror("setsockopt: IPV6_LEAVE_GROUP error");
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The imr6 parameter contains the same structure values used for adding membership.
If multiple sockets request that a node join a particular multicast group, the node remains a member of that multicast group until the last of those sockets is closed.
To receive multicast datagrams sent to a specific UDP port, the receiving socket must be bound to that port using the bind() function. More than one process can receive UDP datagrams destined for the same port if the bind() function is preceded by a setsockopt() function that specifies the SO_REUSEPORT option.
Delivery of IP multicast datagrams to SOCK_RAW sockets is determined by the protocol type of the destination.
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