setsockopt Subroutine

Socket level

Specifies the Level parameter as SOL_SOCKET.

Other levels

Supplies the appropriate protocol number for the protocol controlling the option. For example, to indicate that an option will be interpreted by the TCP protocol, set the Level parameter to the protocol number of TCP, as defined in the netinet/in.h file. Similarly, to indicate that an option will be interpreted by ATM protocol, set the Level parameter to NDDPROTO_ATM, as defined in sys/atmsock.h.

The following list defines socket protocol level options found in the sys/socket.h file:

SO_DEBUG

Turns on recording of debugging information. This option enables or disables debugging in the underlying protocol modules. Set this option in one of the following ways at the command level:

• Use the sodebug command, which turns on or off this option for existing sockets.
• Specify |DEBUG[=level] in the wait/nowait field of a service in inetd.conf in order to turn on this option for the specific service.
• Set the sodebug_env parameter to no, and specify SODEBUG=level in the process environment. This turns on or off this option for all subsequent sockets created by the process.

The value for level can be either min, normal, or detail.

SO_REUSEADDR

Specifies that the rules used in validating addresses supplied by a bind subroutine should allow reuse of a local port.

SO_REUSEADDR allows an application to explicitly deny subsequent bind subroutine to the port/address of the socket with SO_REUSEADDR set. This allows an application to block other applications from binding with the bind subroutine.

SO_REUSEPORT

Specifies that the rules used in validating addresses supplied by a bind subroutine should allow reuse of a local port/address combination. Each binding of the port/address combination must specify the SO_REUSEPORT socket option

SO_CKSUMREV

Enables performance enhancements in the protocol layers. If the protocol supports this option, enabling causes the protocol to defer checksum verification until the user's data is moved into the user's buffer (on recv, recvfrom, read, or recvmsg thread). This can cause applications to be awakened when no data is available, in the case of a checksum error. In this case, EAGAIN is returned. Applications that set this option must handle the EAGAIN error code rturned from a receive call.

SO_KEEPALIVE

Monitors the activity of a connection by enabling or disabling the periodic transmission of ACK messages on a connected socket. The idle interval time can be designated using the TCP/IP no command. Broken connections are discussed in "Understanding Socket Types and Protocols" in Communications Programming Concepts.

SO_DONTROUTE

Does not apply routing on outgoing messages. Indicates that outgoing messages should bypass the standard routing facilities. Instead, they are directed to the appropriate network interface according to the network portion of the destination address.

SO_BROADCAST

Permits sending of broadcast messages.

SO_LINGER

Lingers on a close subroutine if data is present. This option controls the action taken when an unsent messages queue exists for a socket, and a process performs a close subroutine on the socket.

If SO_LINGER is set, the system blocks the process during the close subroutine until it can transmit the data or until the time expires. If SO_LINGER is not specified and a close subroutine is issued, the system handles the call in a way that allows the process to continue as quickly as possible.

The sys/socket.h file defines the linger structure that contains the l_linger member for specifying linger time interval. If linger time is set to anything but 0, the system tries to send any messages queued on the socket. The maximum value that the l_linger member can be set to is 65535. If the application has requested SPEC1170 compliant behavior by exporting the XPG_SUS_ENV environment variable , the linger time is n seconds; otherwise, the linger time is n/100 seconds (ticks), where n is the value of the l_linger member.

SO_OOBINLINE

Leaves received out-of-band data (data marked urgent) in line.

SO_SNDBUF

Sets send buffer size.

SO_RCVBUF

Sets receive buffer size.

SO_SNDLOWAT

Sets send low-water mark.

SO_RCVLOWAT

Sets receive low-water mark.

SO_SNDTIMEO

Sets send time out. This option is setable, but currently not used.

SO_RCVTIMEO

Sets receive time out. This option is setable, but currently not used.

SO_ERROR

Sets the retrieval of error status and clear.

SO_TYPE

Sets the retrieval of a socket type.

The following list defines TCP protocol level options found in the netinet/tcp.h file:

TCP_CWND_IF

Increases the factor of the TCP congestion window (cwnd) during the congestion avoidance. The value must be in the range 0 - 100 (0 is disable). The tcp_cwnd_modified network tunable option must be enabled.

TCP_CWND_DF

Decrease the factor of the TCP cwnd during the congestion avoidance. The value must be in the range 0 - 100 (0 is disable). The tcp_cwnd_modified network tunable option must be enabled.

TCP_NOTENTER_SSTART

Avoids reentering the slow start after the retransmit timeout, which might reset the cwnd to the initial window size, instead of the size of the current slow-start threshold (ss_threshold) value or half of the maximum cwnd (max cwnd/2). The values are 1 for enable and 0 for disable. The tcp_cwnd_modified network tunable option must be enabled.

TCP_ NOREDUCE_CWND_IN_FRXMT

Not decrease the cwnd size when in the fast retransmit phrase. The values are 1 for enable and 0 for disable. The tcp_cwnd_modified network tunable option must be enabled.

TCP_ NOREDUCE_CWND_EXIT_FRXMT

Not decrease the cwnd size when exits the fast retransmit phrase. The values are 1 for enable and 0 for disable. The tcp_cwnd_modified network tunable option must be enabled.

TCP_KEEPCNT

Specifies the maximum number of keepalive packets to be sent to validate a connection. This socket option value is inherited from the parent socket. The default is 8.

TCP_KEEPIDLE

Specifies the number of seconds of idle time on a connection after which TCP sends a keepalive packet. This socket option value is inherited from the parent socket from the accept system call. The default value is 7200 seconds (14400 half seconds).

TCP_KEEPINTVL

Specifies the interval of time between keepalive packets. It is measured in seconds. This socket option value is inherited from the parent socket from the accept system call. The default value is 75 seconds (150 half seconds).

TCP_NODELAY

Specifies whether TCP should follow the Nagle algorithm for deciding when to send data. By default, TCP will follow the Nagle algorithm. To disable this behavior, applications can enable TCP_NODELAY to force TCP to always send data immediately. For example, TCP_NODELAY should be used when there is an application using TCP for a request/response.

TCP_RFC1323

Enables or disables RFC 1323 enhancements on the specified TCP socket. An application might contain the following lines to enable RFC 1323:

int on=1;
setsockopt(s,IPPROTO_TCP,TCP_RFC1323,&on,
           sizeof(on));

TCP_STDURG

Enables or disables RFC 1122 compliant urgent point handling. By default, TCP implements urgent pointer behavior compliant with the 4.2 BSD operating system, i.e., this option defaults to 0.

TCP_NODELAYACK

Specifies if TCP needs to send immediate acknowledgement packets to the sender. If this option is not set, TCP delays sending the acknowledgement packets by up to 200 ms. This allows the acknowledgements to be sent along with the data on a response and minimizes system overhead. Setting this TCP option might cause a slight increase in system overhead, but can result in higher performance for network transfers if the sender is waiting on the receiver's acknowledgements.

TCP protocol level socket options are inherited from listening sockets to new sockets.

The following list defines ATM protocol level options found in the sys/atmsock.h file:

SO_ATM_PARAM

Sets all ATM parameters. This socket option can be used instead of using individual sockets options described below. It uses the connect_ie structure defined in sys/call_ie.h file.

SO_ATM_AAL_PARM

Sets ATM AAL(Adaptation Layer) parameters. It uses the aal_parm structure defined in sys/call_ie.h file.

SO_ATM_TRAFFIC_DES

Sets ATM Traffic Descriptor values. It uses the traffic structure defined in sys/call_ie.h file.

SO_ATM_BEARER

Sets ATM Bearer capability. It uses the bearer structure defined in sys/call_ie.h file.

SO_ATM_BHLI

Sets ATM Broadband High Layer Information. It uses the bhli structure defined in sys/call_ie.h file.

SO_ATM_BLLI

Sets ATM Broadband Low Layer Information. It uses the blli structure defined in sys/call_ie.h file.

SO_ATM_QOS

Sets ATM Quality Of Service values. It uses the qos_parm structure defined in sys/call_ie.h file.

SO_ATM_TRANSIT_SEL

Sets ATM Transit Selector Carrier. It uses the transit_sel structure defined in sys/call_ie.h file.

SO_ATM_ACCEPT

Indicates acceptance of an incoming ATM call, which was indicated to the application via ACCEPT system call. This must be issues for the incoming connection to be fully established. This allows negotiation of ATM parameters.

SO_ATM_MAX_PEND

Sets the number of outstanding transmit buffers that are permitted before an error indication is returned to applications as a result of a transmit operation. This option is only valid for non best effort types of virtual circuits. OptionValue/OptionLength point to a byte which contains the value that this parameter will be set to.

The following list defines IPPROTO_TCP protocol level options found in the netinet/sctp.h file:

SCTP_PEER_ADDR_PARAMS

Enables or disables heartbeats for an association and modifies the heartbeat interval of the association. This option uses the sctp_paddrparams structure defined in the netinet/sctp.h file. For spp_address field, AIX® only supports wildcard address now. The SPP_HB_ENABLE, SPP_HB_DISABLE, and SPP_HB_TIME_ISZERO flags are supported for the spp_flags field. The spp_hbinterval field can be set to a minimum value of 50 milliseconds.

SCTP_MAXSEG

Sets the maximum size of any outgoing SCTP DATA chunk. If the message is larger than the specified size, the message is fragmented by SCTP into the specified size. It uses the sctp_assoc_value structure that is defined in the netinet/sctp.h file.

The following options enable and disable in the same manner:

• SO_DEBUG
• SO_REUSEADDR
• SO_KEEPALIVE
• SO_DONTROUTE
• SO_BROADCAST
• SO_OOBINLINE
• SO_LINGER
• TCP_RFC1323