TCP(4) | Device Drivers Manual | TCP(4) |
tcp
—
#include <sys/socket.h>
#include <netinet/in.h>
int
socket
(AF_INET,
SOCK_STREAM,
0);
int
socket
(AF_INET6,
SOCK_STREAM,
0);
SOCK_STREAM
abstraction. TCP uses the standard Internet address format and, in addition,
provides a per-host collection of “port addresses”. Thus, each
address is composed of an Internet address specifying the host and network,
with a specific TCP port on the host identifying the peer entity.
Sockets using TCP are either “active” or “passive”. Active sockets initiate connections to passive sockets. By default TCP sockets are created active; to create a passive socket the listen(2) system call must be used after binding the socket with the bind(2) system call. Only passive sockets may use the accept(2) call to accept incoming connections. Only active sockets may use the connect(2) call to initiate connections.
Passive sockets may “underspecify” their location to
match incoming connection requests from multiple networks. This technique,
termed “wildcard addressing”, allows a single server to
provide service to clients on multiple networks. To create a socket which
listens on all networks, the Internet address
INADDR_ANY
must be bound. The TCP port may still be
specified at this time; if the port is not specified the system will assign
one. Once a connection has been established the socket's address is fixed by
the peer entity's location. The address assigned the socket is the address
associated with the network interface through which packets are being
transmitted and received. Normally this address corresponds to the peer
entity's network.
TCP supports a number of socket options which can be set with setsockopt(2) and tested with getsockopt(2):
TCP_NODELAY
TCP_NODELAY
(from
<netinet/tcp.h>
, to defeat
this algorithm.TCP_MAXSEG
TCP_MAXSEG
option allows the user to determine the
result of this negotiation, and to reduce it if desired.TCP_MD5SIG
One common use for this in a NetBSD router deployment is to enable based routers to interwork with Cisco equipment at peering points. Support for this feature conforms to RFC 2385. Only IPv4 (AF_INET) sessions are supported.
In order for this option to function correctly, it is necessary for the administrator to add a tcp-md5 key entry to the system's security associations database (SADB) using the setkey(8) utility. This entry must have an SPI of 0x1000 and can therefore only be specified on a per-host basis at this time.
If an SADB entry cannot be found for the destination, the outgoing traffic will have an invalid digest option prepended, and the following error message will be visible on the system console: tcp_signature_compute: SADB lookup failed for %d.%d.%d.%d.
TCP_KEEPIDLE
TCP_KEEPIDLE
option can be used to affect this
value for a given socket, and specifies the number of seconds of idle time
between keepalive probes. This option takes an unsigned
int value, with a value greater than 0.TCP_KEEPINTVL
SO_KEEPALIVE
option is enabled, TCP
probes a connection that has been idle for some amount of time. If the
remote system does not respond to a keepalive probe, TCP retransmits the
probe after some amount of time. The default value for this retransmit
interval is 150 seconds. The TCP_KEEPINTVL
option
can be used to affect this value for a given socket, and specifies the
number of seconds to wait before retransmitting a keepalive probe. This
option takes an unsigned int value, with a value
greater than 0.TCP_KEEPCNT
SO_KEEPALIVE
option is enabled, TCP
probes a connection that has been idle for some amount of time. If the
remote system does not respond to a keepalive probe, TCP retransmits the
probe a certain number of times before a connection is considered to be
broken. The default value for this keepalive probe retransmit limit is 8.
The TCP_KEEPCNT
option can be used to affect this
value for a given socket, and specifies the maximum number of keepalive
probes to be sent. This option takes an unsigned int
value, with a value greater than 0.TCP_KEEPINIT
TCP_KEEPINIT
option can be used to affect this
initial timeout period for a given socket, and specifies the number of
seconds to wait before the connect attempt is timed out. For passive
connections, the TCP_KEEPINIT
option value is
inherited from the listening socket. This option takes an
unsigned int value, with a value greater than
0.TCP_INFO
TPC_INFO
to
getsockopt(2). It
accepts a single argument: a pointer to an instance of
struct tcp_info.
This API is subject to change; consult the source to determine which fields are currently filled out by this option. NetBSD specific additions include send window size, receive window size, and bandwidth-controlled window space.
The option level for the setsockopt(2) call is the protocol number for TCP, available from getprotobyname(3).
In the historical BSD TCP implementation,
if the TCP_NODELAY
option was set on a passive
socket, the sockets returned by
accept(2) erroneously did not
have the TCP_NODELAY
option set; the behavior was
corrected to inherit TCP_NODELAY
in
NetBSD 1.6.
Options at the IP network level may be used with TCP; see ip(4) or ip6(4). Incoming connection requests that are source-routed are noted, and the reverse source route is used in responding.
There are many adjustable parameters that control various aspects of the NetBSD TCP behavior; these parameters are documented in sysctl(7), and they include:
EISCONN
]ENOBUFS
]ETIMEDOUT
]ECONNRESET
]ECONNREFUSED
]EADDRINUSE
]EADDRNOTAVAIL
]Transmission Control Protocol, RFC, 793, September 1981.
Requirements for Internet Hosts -- Communication Layers, RFC, 1122, October 1989.
tcp
protocol stack appeared in
4.2BSD.
February 14, 2015 | NetBSD 9.4 |