tcp.7p (2010 09)

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TCP(7P) TCP(7P)
actually been lost. This option is useful in cases where multiple segments are
dropped. TCP provides a Boolean option, TCP_SACKENA
(from the
<netinet/tcp.h>
header file) to enable or disable this option. This option takes
an
int value.
If
TCP_NODELAY is set, the system sends small amounts of output immediately rather than gathering
them into a single packet after an acknowledgement is received. If
TCP_NODELAY is not set, the system
sends data when it is presented, if there is no outstanding unacknowledged data. If there is outstanding
unacknowledged data, the system gathers small amounts of data to be sent in a single packet once an
acknowledgement is received. For clients such as window managers that send a stream of mouse events
which receive no replies, this packetization may cause significant delays. The
TCP_NODELAY option can
be used to avoid this situation. Note, however, that setting the
TCP_NODELAY option may result in a
large number of small packets being sent over the network.
By default,
TCP_NODELAY is not set when a socket is created.
The option level to use for accessing the TCP option with the
setsockopt() or getsockopt() calls
is the protocol number for TCP which is available from
getprotobyname()
(see getprotoent (3N)).
If the
SO_KEEPALIVE socket option is enabled on an established TCP connection and the connection has
been idle for two hours, TCP sends a packet to the remote socket, expecting the remote TCP to ack-
nowledge that the connection is still active. If the remote TCP does not respond in a timely manner, TCP
continues to send keepalive packets according to its normal retransmission algorithm. If the remote TCP
does not respond within a particular time limit, TCP drops the connection. The next socket system call
(for example, recv()) returns an error, and errno is set to [ETIMEDOUT]. See getsockopt (2) for
details on enabling SO_KEEPALIVE.
The default send and receives buffer size is 32768 bytes (see WARNINGS below). The send and receive
buffer sizes for TCP stream sockets can be altered by using the
SO_SNDBUF and
SO_RCVBUF options of
the
setsockopt() system call or the XTI_SNDBUF and XTI_RCVBUF options of the t_optmgmt()
system call. Refer to getsockopt (2) or t_optmgmt (3) for details.
The maximum transmit buffer size for a TCP stream socket is 2147483647 bytes. The maximum receive
buffer size for a TCP stream socket is 1073725440 bytes. These maximum values can be lowered using
the ndd variables
tcp_xmit_hiwater_max
and tcp_recv_hiwater_max.
ERRORS
One of the following errors may be returned in
errno if a socket operation fails. For a more detailed list
of errors, see the man pages for specific system calls.
[EISCONN] The socket is already connected.
[ENOBUFS] No buffer space is available for an internal data structure.
[ETIMEDOUT] Connection dropped due to excessive retransmissions.
[ECONNRESET]
The connection was forcibly closed by the peer socket.
[ECONNREFUSED]
Remote peer actively refuses connection establishment (usually because no process
is listening to the port).
[EADDRINUSE]
The specified address is already in use.
[EADDRNOTAVAIL]
The specified address is not available on this machine.
WARNINGS
The default socket buffer size might increase without notice in a future release or patch. Therefore, if an
application calls
setsockopt() with SO_RCVBUF, it should do so before calling listen(),orit
should first call getsockopt() with SO_RCVBUF and ensure that the intended new receive buffer size
is not less than the current buffer size. These programming conventions are consistent with TCP protocol
restrictions against reducing the TCP receive window after a connection has been established.
AUTHOR
The socket interfaces to TCP were developed by the University of California, Berkeley.
HP-UX 11i Version 3: September 2010 − 3 − Hewlett-Packard Company 3