setsockopt()--Set Socket Options

Syntax

#include <sys/types.h>
#include <sys/socket.h>

int setsockopt(int socket_descriptor,
               int level,
               int option_name,
               char *option_value,
               int option_length)

Threadsafe: Yes

The setsockopt() function is used to set socket options.

Parameters

socket_descriptor

(Input) The descriptor of the socket for which options are to be set.

level

(Input) Whether the request applies to the socket itself or the underlying protocol being used. Supported values are:

IPPROTO_IP: Request applies to IP protocol layer.
IPPROTO_TCP: Request applies to TCP protocol layer.
NNSPROTO_IPX: Request applies to the IPX protocol layer.
NNSPROTO_SPX: Request applies to the SPX protocol layer.
SOL_SOCKET: Request applies to socket layer.

option_name

(Input) The name of the option to be set. The following tables list the options supported for each level. Assume that the option is supported for all address families unless the option is described otherwise.

Note: Options directed to a specific protocol level are only supported by that protocol. An option that is directed to the SOL_SOCKET level always completes successfully. This provides compatibility with Berkeley Software Distributions implementations that also shield the application from protocols that do not support an option.

Figure 1-13. Socket Options That Apply to the IP Layer (IPPROTO_IP)

Option Description
IP_OPTIONS Set IP header options. This is only supported for sockets with an address family of AF_INET.
IP_TOS Set Type Of Service (TOS) and Precedence in the IP header. This option is only supported for sockets with an address family of AF_INET.
IP_TTL Set Time To Live (TTL) in the IP header. This option is only supported for sockets with an address family AF_INET. IP_MULTICAST_IF Set interface over which outgoing multicast datagrams should be sent. An option_value parameter of type in_addr is used to specify the local IP address that is associated with the interface over which outgoing multicast datagrams should be sent. An address of INADDR_ANY removes the previous selection. This option is only supported for sockets with an address family of AF_INET and type of SOCK_DGRAM or SOCK_RAW. IP_MULTICAST_TTL Set Time To Live (TTL) in the IP header for outgoing multicast datagrams. An option_value parameter of type char is used to set this value between 0 and 255. This option is only supported for sockets with an address family of AF_INET and type of SOCK_DGRAM or SOCK_RAW. IP_MULTICAST_LOOP Specify that a copy of an outgoing multicast datagram should be delivered to the sending host as long as it is a member of the multicast group. If this option is not set, a copy of the datagram will not be delivered to the sending host. An option_value parameter of type char is used to control loopback being on or off. This option is only supported for sockets with an address family of AF_INET and type of SOCK_DGRAM or SOCK_RAW. IP_ADD_MEMBERSHIP Joins a multicast group as specified in the option_value parameter of type struct ip_mreq. A maximum of IP_MAX_MEMBERSHIPS groups may be joined per socket. This option is only supported for sockets with an address family of AF_INET and type of SOCK_DGRAM or SOCK_RAW. IP_DROP_MEMBERSHIP Leaves a multicast group as specified in the option_value parameter of type struct ip_mreq. This option is only supported for sockets with an address family of AF_INET and type of SOCK_DGRAM or SOCK_RAW. IP_RECVLCLIFADDR Indicates if the local interface that a datagram to be received should be returned. A value of 1 indicates the first 4 bytes of the reserved field of the sockaddr structure will contain the local interface. This option is only supported for sockets with an address family of AF_INET and type of SOCK_DGRAM.
IP_SETPMTU Enable or disable path MTU discovery. This option is supported for sockets with an address family of AF_INET and type of SOCK_DGRAM only.
IP_DONTFRAG Set or reset the don't fragment flag in the IP header. This option is supported for sockets with an address family of AF_INET and type of SOCK_DGRAM only.

Option	Description
`IP_OPTIONS`	Set IP header options. This is only supported for sockets with an address family of `AF_INET`.
`IP_TOS`	Set Type Of Service (TOS) and Precedence in the IP header. This option is only supported for sockets with an address family of `AF_INET`.
`IP_TTL`	Set Time To Live (TTL) in the IP header. This option is only supported for sockets with an address family `AF_INET`.	`IP_MULTICAST_IF`	Set interface over which outgoing multicast datagrams should be sent. An option_value parameter of type in_addr is used to specify the local IP address that is associated with the interface over which outgoing multicast datagrams should be sent. An address of INADDR_ANY removes the previous selection. This option is only supported for sockets with an address family of `AF_INET` and type of `SOCK_DGRAM` or `SOCK_RAW`.	`IP_MULTICAST_TTL`	Set Time To Live (TTL) in the IP header for outgoing multicast datagrams. An option_value parameter of type char is used to set this value between 0 and 255. This option is only supported for sockets with an address family of `AF_INET` and type of `SOCK_DGRAM` or `SOCK_RAW`.	`IP_MULTICAST_LOOP`	Specify that a copy of an outgoing multicast datagram should be delivered to the sending host as long as it is a member of the multicast group. If this option is not set, a copy of the datagram will not be delivered to the sending host. An option_value parameter of type char is used to control loopback being on or off. This option is only supported for sockets with an address family of `AF_INET` and type of `SOCK_DGRAM` or `SOCK_RAW`.	`IP_ADD_MEMBERSHIP`	Joins a multicast group as specified in the option_value parameter of type struct ip_mreq. A maximum of IP_MAX_MEMBERSHIPS groups may be joined per socket. This option is only supported for sockets with an address family of `AF_INET` and type of `SOCK_DGRAM` or `SOCK_RAW`.	`IP_DROP_MEMBERSHIP`	Leaves a multicast group as specified in the option_value parameter of type struct ip_mreq. This option is only supported for sockets with an address family of `AF_INET` and type of `SOCK_DGRAM` or `SOCK_RAW`.	IP_RECVLCLIFADDR	Indicates if the local interface that a datagram to be received should be returned. A value of 1 indicates the first 4 bytes of the reserved field of the sockaddr structure will contain the local interface. This option is only supported for sockets with an address family of AF_INET and type of SOCK_DGRAM.
`IP_SETPMTU`	Enable or disable path MTU discovery. This option is supported for sockets with an address family of `AF_INET` and type of `SOCK_DGRAM` only.
`IP_DONTFRAG`	Set or reset the don't fragment flag in the IP header. This option is supported for sockets with an address family of `AF_INET` and type of `SOCK_DGRAM` only.

Figure 1-14. Socket Options That Apply to the TCP Layer (IPPROTO_TCP)

Option Description
TCP_NODELAY Indicates if TCP is to buffer data. This option is only supported for sockets with an address family of AF_INET and type of SOCK_STREAM.

Option	Description
`TCP_NODELAY`	Indicates if TCP is to buffer data. This option is only supported for sockets with an address family of `AF_INET` and type of `SOCK_STREAM`.

Figure 1-15. Socket Options That Apply to the IPX or SPX Layer (NNSPROTO_IPX or NNSPROTO_SPX)

Option Description
SO_HEADERS_ON_INPUT Request the transport to deliver the received protocol headers with the data on input operations such as recv(). This is only supported for sockets with an address family of AF_NS and a type of SOCK_SEQPACKET or SOCK_DGRAM. If the type is SOCK_SEQPACKET, this option requests that the transport place the SPX headers received with the data packets in the first 12 bytes of the supplied user buffer on input operations. The default is that the option be set on. If the type is SOCK_DGRAM, this option requests that the transport place the IPX headers received with the data packets in the first 30 bytes of the supplied user buffer on input operations. The default is that the option be set off. Changing the setting of this option does not affect packets that have already been received by the system and are waiting to be delivered to your application.
SO_HEADERS_ON_OUTPUT Request the transport to accept the protocol header as the first 12 or 30 bytes of data in the user-supplied buffer on output operations such as send(). This is only supported for sockets with an address family of AF_NS and a type of SOCK_SEQPACKET or SOCK_DGRAM. If the type is SOCK_SEQPACKET, the user must supply the SPX header as the first 12 bytes of the buffer on output operations. Only the end of message indicator and data stream type fields of the specified header are used. The default is that the option be set on. If the type is SOCK_DGRAM, the user must supply the IPX header as the first 30 bytes of the buffer on output operations. All fields of the specified header will be used except checksum and packet length. The default is that the option be set off. Changing this option does not affect packets that have been sent by your application but have not yet been transmitted because of flow control or other reasons.
SO_DEFAULT_HEADERS Specify the default protocol header to be used on output operations. This is only supported for sockets with an address family of AF_NS and a type of SOCK_SEQPACKET, SOCK_STREAM, or SOCK_DGRAM. For type SOCK_SEQPACKET or SOCK_STREAM, this is a default 12-byte SPX header. Only the end of message indicator and data stream type fields of the specified header are used. For type SOCK_DGRAM, this is a default 30-byte IPX header. Only the packet type field of the specified header is used.

Option	Description
`SO_HEADERS_ON_INPUT`	Request the transport to deliver the received protocol headers with the data on input operations such as recv(). This is only supported for sockets with an address family of `AF_NS` and a type of `SOCK_SEQPACKET` or `SOCK_DGRAM`. If the type is `SOCK_SEQPACKET`, this option requests that the transport place the SPX headers received with the data packets in the first 12 bytes of the supplied user buffer on input operations. The default is that the option be set on. If the type is `SOCK_DGRAM`, this option requests that the transport place the IPX headers received with the data packets in the first 30 bytes of the supplied user buffer on input operations. The default is that the option be set off. Changing the setting of this option does not affect packets that have already been received by the system and are waiting to be delivered to your application.
`SO_HEADERS_ON_OUTPUT`	Request the transport to accept the protocol header as the first 12 or 30 bytes of data in the user-supplied buffer on output operations such as send(). This is only supported for sockets with an address family of `AF_NS` and a type of `SOCK_SEQPACKET` or `SOCK_DGRAM`. If the type is `SOCK_SEQPACKET`, the user must supply the SPX header as the first 12 bytes of the buffer on output operations. Only the end of message indicator and data stream type fields of the specified header are used. The default is that the option be set on. If the type is `SOCK_DGRAM`, the user must supply the IPX header as the first 30 bytes of the buffer on output operations. All fields of the specified header will be used except checksum and packet length. The default is that the option be set off. Changing this option does not affect packets that have been sent by your application but have not yet been transmitted because of flow control or other reasons.
`SO_DEFAULT_HEADERS`	Specify the default protocol header to be used on output operations. This is only supported for sockets with an address family of `AF_NS` and a type of `SOCK_SEQPACKET`, `SOCK_STREAM`, or `SOCK_DGRAM`. For type `SOCK_SEQPACKET` or `SOCK_STREAM`, this is a default 12-byte SPX header. Only the end of message indicator and data stream type fields of the specified header are used. For type `SOCK_DGRAM`, this is a default 30-byte IPX header. Only the packet type field of the specified header is used.

Figure 1-16. Socket Options That Apply to the SPX Layer Only (NNSPROTO_SPX)

Option Description
SO_MTU Change the maximum transmission unit (MTU) size. This is only supported for sockets with an address family of AF_NS and a type of SOCK_SEQPACKET or SOCK_STREAM.

Option	Description
`SO_MTU`	Change the maximum transmission unit (MTU) size. This is only supported for sockets with an address family of `AF_NS` and a type of `SOCK_SEQPACKET` or `SOCK_STREAM`.

Figure 1-17. Socket Options That Apply to the Socket Layer (SOL_SOCKET )

Option Description
SO_BROADCAST Enable the socket for issuing messages to a broadcast address. This option is only supported for sockets with an address family of AF_INET and type SOCK_DGRAM or SOCK_RAW, or an address family of AF_NS and type SOCK_DGRAM. For sockets with an address family of AF_INET, the broadcast address to be used may be determined by issuing an ioctl() with the SIOCGIFBRDADDR request.
SO_DEBUG Indicates if low level-debugging is active. This option is not supported.
SO_DONTROUTE Bypass normal routing mechanisms. This option is only supported by sockets with an address family of AF_INET or AF_NS.
SO_KEEPALIVE Keep the connection up by sending periodic transmissions. This option is only supported for sockets of an address family of AF_INET and type SOCK_STREAM, or an address family of AF_NS and a type of SOCK_SEQPACKET or SOCK_STREAM.
SO_LINGER Indicates if the system attempts delivery of any buffered data or if the system discards it when a close() is issued.
For sockets that are using a connection-oriented transport service with an address family of AF_NS or AF_INET, the default is off (which means that the system attempts to send any queued data, with an infinite wait-time).
For sockets that are using a connection-oriented transport service with an address family of AF_TELEPHONY, the default is on with a linger time of 1 second (which means that the system will wait up to 1 second to send buffered data before clearing the telephone connection).
SO_OOBINLINE Indicates whether out-of-band data is received inline with normal data. This option is only supported for sockets with an address family of AF_INET or AF_NS.
SO_RCVBUF Set the size of the receive buffer.
SO_RCVLOWAT Set the size of the receive low-water mark. The default size is 1. This option is only supported for sockets with an address family of AF_NET and type of SOCK_STREAM.
SO_RCVTIMEO Set the receive timeout value. This option is not supported.
SO_REUSEADDR Indicates if the local socket address can be reused. This option is supported by sockets with an address family of AF_INET and a type of SOCK_STREAM or SOCK_DGRAM. It is also supported for sockets with an address family of AF_NS and a type of SOCK_SEQPACKET or SOCK_STREAM.
SO_SNDBUF Set the size of the send buffer.
SO_SNDLOWAT Set the size of the send low-water mark. This option is not supported.
SO_SNDTIMEO Set the send timeout value. This option is not supported.
SO_USELOOPBACK Indicates if the loopback feature is being used. This option is not supported.

option_value

Option	Description
`SO_BROADCAST`	Enable the socket for issuing messages to a broadcast address. This option is only supported for sockets with an address family of `AF_INET` and type `SOCK_DGRAM` or `SOCK_RAW`, or an address family of `AF_NS` and type `SOCK_DGRAM`. For sockets with an address family of `AF_INET`, the broadcast address to be used may be determined by issuing an ioctl() with the `SIOCGIFBRDADDR` request.
`SO_DEBUG`	Indicates if low level-debugging is active. This option is not supported.
`SO_DONTROUTE`	Bypass normal routing mechanisms. This option is only supported by sockets with an address family of `AF_INET` or `AF_NS`.
`SO_KEEPALIVE`	Keep the connection up by sending periodic transmissions. This option is only supported for sockets of an address family of `AF_INET` and type `SOCK_STREAM`, or an address family of `AF_NS` and a type of `SOCK_SEQPACKET` or `SOCK_STREAM`.
`SO_LINGER`	Indicates if the system attempts delivery of any buffered data or if the system discards it when a close() is issued. For sockets that are using a connection-oriented transport service with an address family of `AF_NS` or `AF_INET`, the default is off (which means that the system attempts to send any queued data, with an infinite wait-time). For sockets that are using a connection-oriented transport service with an address family of `AF_TELEPHONY`, the default is on with a linger time of 1 second (which means that the system will wait up to 1 second to send buffered data before clearing the telephone connection).
`SO_OOBINLINE`	Indicates whether out-of-band data is received inline with normal data. This option is only supported for sockets with an address family of `AF_INET` or `AF_NS`.
`SO_RCVBUF`	Set the size of the receive buffer.
SO_RCVLOWAT	Set the size of the receive low-water mark. The default size is 1. This option is only supported for sockets with an address family of AF_NET and type of SOCK_STREAM.
`SO_RCVTIMEO`	Set the receive timeout value. This option is not supported.
`SO_REUSEADDR`	Indicates if the local socket address can be reused. This option is supported by sockets with an address family of `AF_INET` and a type of `SOCK_STREAM` or `SOCK_DGRAM`. It is also supported for sockets with an address family of `AF_NS` and a type of `SOCK_SEQPACKET` or `SOCK_STREAM`.
`SO_SNDBUF`	Set the size of the send buffer.
`SO_SNDLOWAT`	Set the size of the send low-water mark. This option is not supported.
`SO_SNDTIMEO`	Set the send timeout value. This option is not supported.
`SO_USELOOPBACK`	Indicates if the loopback feature is being used. This option is not supported.

(Input) A pointer to the option value. Integer flags/values are required by setsockopt() for all the socket options except SO_LINGER , IP_OPTIONS , IP_MULTICAST_IF , IP_MULTICAST_TTL, IP_MULTICAST_LOOP, IP_ADD_MEMBERSHIP, IP_DROP_MEMBERSHIP, and SO_DEFAULT_HEADERS .

Note: For the IP_TOS and IP_TTL options, only the rightmost octet (least significant octet) of the integer value is used.

The following options can be set by specifying a nonzero value for the option_value parameter:

SO_BROADCAST
SO_DEBUG
SO_DONTROUTE
SO_HEADERS_ON_INPUT
SO_HEADERS_ON_OUTPUT
SO_KEEPALIVE
SO_MTU
SO_OOBINLINE
SO_REUSEADDR
TCP_NODELAY
IP_MULTICAST_LOOP
IP_DONTFRAG
IP_SETPMTU

For the SO_LINGER option, option_value is a pointer to the structure struct linger, defined in <sys/socket.h>.

      struct linger [
        int        l_onoff;
        int        l_linger;
      ];

The l_onoff field determines if the linger option is set. A nonzero value indicates the linger option is set and is using the l_linger value. A zero value indicates that the option is not set. The l_linger field is the time to wait before any buffered data to be sent is discarded. The following occur on a close():

For AF_INET and AF_NS sockets:
- If the l_onoff value is zero, the system attempts to send any buffered data with an infinite wait-time.
- If the l_onoff value is nonzero and the l_linger value is nonzero, the system attempts to send any buffered data for l_linger time. If l_linger time has elapsed and the data is still not successfully sent, it is discarded. When data is discarded, the remote program may receive a [ECONNRESET].
- For AF_INET sockets over SNA, if the l_onoff value is nonzero and the l_linger value is zero, the system waits indefinitely (no timer is implemented). Otherwise, if the l_onoff value is nonzero and the l_linger value is zero, the system discards any buffered data. When data is discarded, the remote program may receive a [ECONNRESET] (or [ECONNABORTED] for AF_NS sockets).
For AF_TELEPHONY sockets:
- If the l_onoff value is zero, the system will wait until all buffered data is sent or 1 second has elapsed, whichever occurs first, before clearing the telephone connection (that is, hanging up).
- If the l_onoff value is nonzero, the system will wait until all buffered data is sent or l_linger seconds have elapsed, whichever occurs first, before clearing the telephone connection (that is, hanging up).

Note: An application must implement an application level confirmation. Guaranteed receipt of data by the partner program is required. Setting SO_LINGER does not guarantee delivery.

For the IP_OPTIONS option, option_value is a pointer to a character string representing the IP options as specified in RFC 791. The character string varies depending on which options are selected. Each option is made up of a single byte representing the option code, and may be followed by a length field (1 byte) and data for the option. The IP options that can be set are:

End of option list. Used if options do not end at end of header.
No operation (used to align octets in a list of options).
Security and handling restrictions.
Loose source routing. Used to route a datagram along a path of specified IP addresses. Multiple network hops are allowed between any two IP addresses on the path.
Record route. Used to trace a route.
Stream identifier. Used to carry a SATNET stream identifier. This option has been deprecated by RFC 1122 and will result in an error of [EINVAL] if used.
Strict source routing. Used to route datagram along a path of specified IP addresses. No additional network hops are allowed between any two IP addresses in the path.
Internet timestamp. Used to record timestamps along the route.

For the IP_MULTICAST_IF option, option_value is a pointer to the structure in_addr, defined in <netinet/in.h> as:


    struct in_addr [
      u_long  s_addr;
          /* IP address                  */
    ];

The s_addr field specifies the local IP address that is associated with the interface over which outgoing multicast datagrams should be sent.

For the IP_ADD_MEMBERSHIP and IP_DROP_MEMBERSHIP options, option_value is a pointer to the structure ip_mreq, defined in <netinet/in.h> as:


    struct ip_mreq [
      struct in_addr imr_multiaddr;
          /* IP multicast address of group */
      struct in_addr imr_interface;
          /* local IP address of interface */
   ];

The imr_multiaddr field is used to specify the multicast group to join or leave. The imr_interface field is used to specify the local IP address that is associated with the interface to which this request applies. If INADDR_ANY is specified for the local interface, the default multicast interface will be selected.

Note: Reception of IP multicast datagrams may require configuration changes to the line description to enable the adapter to receive packets with a multicast destination address. On Ethernet, for example, the Ethernet group address that is associated with the IP group address must be specified by the GRPADR parameter on the line description. To determine the Ethernet group address for a particular IP group address, the low-order 23 bits of the IP address are placed into the low-order 23 bits of the Ethernet group address 01.00.5E.xx.xx.xx.

Notes:

For sockets that use a connection-oriented transport service, IP options that are set using setsockopt() are only used if they are set prior to a connect() being issued. After the connection is established, any IP options that the user sets are ignored.
If the IP options portion contains a source routing option, then the address in the source routing option overrides the destination address. The destination address may have been specified on an output operation (for example, on a sendto()) or on a connect().
If a socket has a type of SOCK_RAW and a protocol of IPPROTO_RAW, any IP options set using setsockopt() are ignored (since the user must supply the IP header data on an output operation as part of the data that is being transmitted).

For the SO_DEFAULT_HEADERS option where level is specified as NNSPROTO_IPX, option_value is a pointer to where the structure idp is stored. The structure idp is defined in <netns/idp.h>. For the SO_DEFAULT_HEADERS option where level is specified as NNSPROTO_SPX, option_value is a pointer to where the structure sphdr is stored. The structure sphdr is defined in <netns/sp.h>.

option_length

(Input) The length of the option_value.

Return Value

setsockopt() returns an integer. Possible values are:

-1 (unsuccessful)
0 (successful)

Error Conditions

When setsockopt() fails, errno can be set to one of the following:

[EADDRINUSE]

Address already in use.
This error code indicates that the socket_descriptor parameter specified for the IP_ADD_MEMBERSHIP operation is already a member of the specified multicast group.

[EADDRNOTAVAIL]

Address not available.
For the IP_ADD_MEMBERSHIP or IP_DROP_MEMBERSHIP operations, this error code indicates that an incorrect address was specified for either the imr_multiaddr or imr_interface parameter value.

[EBADF]

Descriptor not valid.

[ECONNABORTED]

Connection ended abnormally.

This error code indicates that the transport provider ended the connection abnormally because of one of the following:

The retransmission limit has been reached for data that was being sent on the socket.
A protocol error was detected.
For AF_NS sockets, a timeout occurred.

[EFAULT]

Bad address.

The system detected an address which was not valid while attempting to access the option_value parameter.

[EINVAL]

Parameter not valid.

This error code indicates one of the following:

The level parameter specifies a level that is not supported.
The option_name parameter specifies a value that is not valid (except for when the level is SOL_SOCKET , in which case [ENOPROTOOPT] is returned).
The option_value parameter specifies a value that is not valid.
The option_length parameter specifies a negative or zero value.
An attempt was made to set a socket option that was read-only.

[EIO]

Input/output error.

[ENOBUFS]

There is not enough buffer space for the requested operation.

[ENOPROTOOPT]

The protocol does not support the specified option.

This error code indicates one of the following:

The socket has an address family of AF_UNIX and the level parameter specified is not SOL_SOCKET .
The level parameter specifies a level of SOL_SOCKET and the option_name parameter specifies a value that is not valid.

[ENOTCONN]

Requested operation requires a connection.

This error code is only returned if the level parameter specifies a level other than SOL_SOCKET and the socket_descriptor parameter points to a socket that is using a connection-oriented transport service that has had its connection broken.

[ENOTSOCK]

The specified descriptor does not reference a socket.

[EPERM]

Operation not permitted.

The executing user profile must have *IOSYSCFG special authority to set options when the level parameter specifies IPPROTO_IP and the option_value parameter is IP_OPTIONS .

[ETOOMANYREFS]

The operation would have exceeded the maximum number of references allowed for this socket.

[EUNATCH]

The protocol required to support the specified address family is not available at this time.

[EUNKNOWN]

Unknown system state.

Error Messages

CPE3418 E: Possible APAR condition or hardware failure.
CPF9872 E: Program or service program &1 in library &2 ended. Reason code &3.
CPFA081 E: Unable to set return value or error code.

Usage Notes

Socket options are defined in <sys/socket.h>, IP options are defined in <netinet/ip.h> and <netinet/in.h>, TCP options are defined in <netinet/tcp.h>, and SPX and IPX options are defined in <netns/ns.h>.
The user profile for an application that is running must have *IOSYSCFG special authority to set options when the level parameter specifies IPPROTO_IP and the option_value parameter is IP_OPTIONS .
The following comments applies to the SO_SNDBUF option value:
- For AF_INET sockets over TCP of type SOCK_STREAM, the maximum value the SO_SNDBUF option can be set to is 8 megabytes. Anything greater results in an error of [ENOBUFS]. If the SO_SNDBUF option value is set to a positive value that is less than 512 bytes, the system automatically uses 512 bytes as the SO_SNDBUF size.
- For AF_INET sockets over UDP of type SOCK_DGRAM, the maximum value the SO_SNDBUF option can be set to is 65535 bytes less the IP and UDP header sizes. Anything greater results in an error of [EINVAL].
For AF_INET sockets over SNA of type SOCK_STREAM, SO_RCVBUF should be set before connection is established. After connection is established, any changes are ignored. Also, only the client can affect the receive buffer size. The server cannot affect it.
For AF_INET sockets over SNA of type SOCK_DGRAM, both SO_SNDBUF and SO_RCVBUF are ignored and have no effect on processing.
When a TCP connection is closed for a socket using the AF_INET address family, the port associated with that connection is not made available until twice the Maximum Segment Life (MSL) time in seconds has passed. The MSL time is approximately 2 minutes. The SO_REUSEADDR option allows a bind() to succeed when requesting a port that is being held during this time frame. This can be especially useful if a server is abruptly ended and restarted.
Notes:
1. For AF_INET SOCK_STREAM sockets, this option does not allow two servers to successfully issue a bind() requesting the same port number and local address combination. For AF_INET SOCK_DGRAM sockets, the SO_REUSEADDR option does allow multiple servers to successfully bind to the same port. When broadcast or multicast datagrams are received for a given port, each server that is bound to that port receives a copy of the datagram provided each server has enabled the SO_REUSEADDR option.
2. This option does not affect unicast datagram delivery.
The following SOL_SOCKET options are not supported by AF_INET sockets over SNA. setsockopt() appears to succeed, but has no effect on the function of AF_INET sockets over SNA.
- SO_BROADCAST
- SO_DONTROUTE
- SO_KEEPALIVE
- SO_LINGER
The path MTU discovery options, IP_DONTFRAG and IP_SETPMTU , are not valid for multicast group destinations.
Only the following SOL_SOCKET options are supported by AF_TELEPHONY sockets. For the others, setsockopt() appears to succeed, but has no effect on the function of the AF_TELEPHONY sockets.
- SO_RCVBUF
- SO_SNDBUF
- SO_LINGER

Related Information
getsockopt()--Retrieve Information about Socket Options

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