mdoc(7) police: Tidy up the formatting.
This commit is contained in:
Ruslan Ermilov
parent
17ce5b94d6
commit
e91fabac7b
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=112496
@ -32,7 +32,7 @@
|
||||
.\" From: @(#)tcp.4 8.1 (Berkeley) 6/5/93
|
||||
.\" $FreeBSD$
|
||||
.\"
|
||||
.Dd February 14, 1995
|
||||
.Dd March 13, 2003
|
||||
.Dt TCP 4
|
||||
.Os
|
||||
.Sh NAME
|
||||
@ -48,37 +48,43 @@
|
||||
The
|
||||
.Tn TCP
|
||||
protocol provides reliable, flow-controlled, two-way
|
||||
transmission of data. It is a byte-stream protocol used to
|
||||
transmission of data.
|
||||
It is a byte-stream protocol used to
|
||||
support the
|
||||
.Dv SOCK_STREAM
|
||||
abstraction. TCP uses the standard
|
||||
abstraction.
|
||||
.Tn TCP
|
||||
uses the standard
|
||||
Internet address format and, in addition, provides a per-host
|
||||
collection of
|
||||
.Dq port addresses .
|
||||
.Dq "port addresses" .
|
||||
Thus, each address is composed
|
||||
of an Internet address specifying the host and network, with
|
||||
a specific
|
||||
of an Internet address specifying the host and network,
|
||||
with a specific
|
||||
.Tn TCP
|
||||
port on the host identifying the peer entity.
|
||||
.Pp
|
||||
Sockets utilizing the tcp protocol are either
|
||||
Sockets utilizing the
|
||||
.Tn TCP
|
||||
protocol are either
|
||||
.Dq active
|
||||
or
|
||||
.Dq passive .
|
||||
Active sockets initiate connections to passive
|
||||
sockets. By default
|
||||
sockets.
|
||||
By default,
|
||||
.Tn TCP
|
||||
sockets are created active; to create a
|
||||
passive socket the
|
||||
passive socket, the
|
||||
.Xr listen 2
|
||||
system call must be used
|
||||
after binding the socket with the
|
||||
.Xr bind 2
|
||||
system call. Only
|
||||
passive sockets may use the
|
||||
system call.
|
||||
Only passive sockets may use the
|
||||
.Xr accept 2
|
||||
call to accept incoming connections. Only active sockets may
|
||||
use the
|
||||
call to accept incoming connections.
|
||||
Only active sockets may use the
|
||||
.Xr connect 2
|
||||
call to initiate connections.
|
||||
.Tn TCP
|
||||
@ -90,30 +96,32 @@ which is described in
|
||||
Passive sockets may
|
||||
.Dq underspecify
|
||||
their location to match
|
||||
incoming connection requests from multiple networks. This
|
||||
technique, termed
|
||||
.Dq wildcard addressing ,
|
||||
incoming connection requests from multiple networks.
|
||||
This technique, termed
|
||||
.Dq "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
|
||||
.Dv INADDR_ANY
|
||||
must be bound. The
|
||||
must be bound.
|
||||
The
|
||||
.Tn 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
|
||||
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 to 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.
|
||||
through which packets are being transmitted and received.
|
||||
Normally, this address corresponds to the peer entity's network.
|
||||
.Pp
|
||||
.Tn TCP
|
||||
supports a number of socket options which can be set with
|
||||
.Xr setsockopt 2
|
||||
and tested with
|
||||
.Xr getsockopt 2 :
|
||||
.Bl -tag -width TCP_NODELAYx
|
||||
.Bl -tag -width ".Dv TCP_NODELAY"
|
||||
.It Dv TCP_NODELAY
|
||||
Under most circumstances,
|
||||
.Tn TCP
|
||||
@ -128,9 +136,11 @@ The boolean option
|
||||
.Dv TCP_NODELAY
|
||||
defeats this algorithm.
|
||||
.It Dv TCP_MAXSEG
|
||||
By default, a sender\- and receiver-TCP
|
||||
By default, a sender- and
|
||||
.No receiver- Ns Tn TCP
|
||||
will negotiate among themselves to determine the maximum segment size
|
||||
to be used for each connection. The
|
||||
to be used for each connection.
|
||||
The
|
||||
.Dv TCP_MAXSEG
|
||||
option allows the user to determine the result of this negotiation,
|
||||
and to reduce it if desired.
|
||||
@ -139,17 +149,18 @@ and to reduce it if desired.
|
||||
usually sends a number of options in each packet, corresponding to
|
||||
various
|
||||
.Tn TCP
|
||||
extensions which are provided in this implementation. The boolean
|
||||
option
|
||||
extensions which are provided in this implementation.
|
||||
The boolean option
|
||||
.Dv TCP_NOOPT
|
||||
is provided to disable
|
||||
.Tn TCP
|
||||
option use on a per-connection basis.
|
||||
.It Dv TCP_NOPUSH
|
||||
By convention, the sender-TCP
|
||||
By convention, the
|
||||
.No sender- Ns Tn TCP
|
||||
will set the
|
||||
.Dq push
|
||||
bit and begin transmission immediately (if permitted) at the end of
|
||||
bit, and begin transmission immediately (if permitted) at the end of
|
||||
every user call to
|
||||
.Xr write 2
|
||||
or
|
||||
@ -157,9 +168,10 @@ or
|
||||
The
|
||||
.Dv TCP_NOPUSH
|
||||
option is provided to allow servers to easily make use of Transaction
|
||||
TCP (see
|
||||
.Tn TCP
|
||||
(see
|
||||
.Xr ttcp 4 ) .
|
||||
When the option is set to a non-zero value,
|
||||
When this option is set to a non-zero value,
|
||||
.Tn TCP
|
||||
will delay sending any data at all until either the socket is closed,
|
||||
or the internal send buffer is filled.
|
||||
@ -184,65 +196,74 @@ see
|
||||
.Xr ip 4 .
|
||||
Incoming connection requests that are source-routed are noted,
|
||||
and the reverse source route is used in responding.
|
||||
.Sh MIB VARIABLES
|
||||
.Ss MIB Variables
|
||||
The
|
||||
.Nm
|
||||
.Tn TCP
|
||||
protocol implements a number of variables in the
|
||||
.Li net.inet
|
||||
.Va net.inet.tcp
|
||||
branch of the
|
||||
.Xr sysctl 3
|
||||
MIB.
|
||||
.Bl -tag -width TCPCTL_DO_RFC1644
|
||||
.Bl -tag -width ".Va TCPCTL_DO_RFC1644"
|
||||
.It Dv TCPCTL_DO_RFC1323
|
||||
.Pq tcp.rfc1323
|
||||
.Pq Va rfc1323
|
||||
Implement the window scaling and timestamp options of RFC 1323
|
||||
(default true).
|
||||
(default is true).
|
||||
.It Dv TCPCTL_DO_RFC1644
|
||||
.Pq tcp.rfc1644
|
||||
.Pq Va rfc1644
|
||||
Implement Transaction
|
||||
.Tn TCP ,
|
||||
as described in RFC 1644.
|
||||
.It Dv TCPCTL_MSSDFLT
|
||||
.Pq tcp.mssdflt
|
||||
.Pq Va mssdflt
|
||||
The default value used for the maximum segment size
|
||||
.Pq Dq MSS
|
||||
when no advice to the contrary is received from MSS negotiation.
|
||||
.It Dv TCPCTL_SENDSPACE
|
||||
.Pq tcp.sendspace
|
||||
Maximum TCP send window.
|
||||
.Pq Va sendspace
|
||||
Maximum
|
||||
.Tn TCP
|
||||
send window.
|
||||
.It Dv TCPCTL_RECVSPACE
|
||||
.Pq tcp.recvspace
|
||||
Maximum TCP receive window.
|
||||
.It tcp.log_in_vain
|
||||
.Pq Va recvspace
|
||||
Maximum
|
||||
.Tn TCP
|
||||
receive window.
|
||||
.It Va log_in_vain
|
||||
Log any connection attempts to ports where there is not a socket
|
||||
accepting connections.
|
||||
The value of 1 limits the logging to SYN (connection establishment)
|
||||
packets only.
|
||||
That of 2 results in any TCP packets to closed ports being logged.
|
||||
The value of 1 limits the logging to
|
||||
.Tn SYN
|
||||
(connection establishment) packets only.
|
||||
That of 2 results in any
|
||||
.Tn TCP
|
||||
packets to closed ports being logged.
|
||||
Any value unlisted above disables the logging
|
||||
(default is 0, i.e., the logging is disabled).
|
||||
.It tcp.slowstart_flightsize
|
||||
.It Va slowstart_flightsize
|
||||
The number of packets allowed to be in-flight during the
|
||||
.Tn TCP
|
||||
slow-start phase on a non-local network.
|
||||
.It tcp.local_slowstart_flightsize
|
||||
.It Va local_slowstart_flightsize
|
||||
The number of packets allowed to be in-flight during the
|
||||
.Tn TCP
|
||||
slow-start phase to local machines in the same subnet.
|
||||
.It tcp.msl
|
||||
.It Va msl
|
||||
The Maximum Segment Lifetime, in milliseconds, for a packet.
|
||||
.It tcp.keepinit
|
||||
Timeout, in milliseconds, for new, non-established TCP connections.
|
||||
.It tcp.keepidle
|
||||
.It Va keepinit
|
||||
Timeout, in milliseconds, for new, non-established
|
||||
.Tn TCP
|
||||
connections.
|
||||
.It Va keepidle
|
||||
Amount of time, in milliseconds, that the connection must be idle
|
||||
before keepalive probes (if enabled) are sent.
|
||||
.It tcp.keepintvl
|
||||
.It Va keepintvl
|
||||
The interval, in milliseconds, between keepalive probes sent to remote
|
||||
machines.
|
||||
After
|
||||
.Dv TCPTV_KEEPCNT
|
||||
(default 8) probes are sent, with no response, the connection is dropped.
|
||||
.It tcp.always_keepalive
|
||||
.It Va always_keepalive
|
||||
Assume that
|
||||
.Dv SO_KEEPALIVE
|
||||
is set on all
|
||||
@ -250,34 +271,36 @@ is set on all
|
||||
connections, the kernel will
|
||||
periodically send a packet to the remote host to verify the connection
|
||||
is still up.
|
||||
.It tcp.icmp_may_rst
|
||||
.It Va icmp_may_rst
|
||||
Certain
|
||||
.Tn ICMP
|
||||
unreachable messages may abort connections in
|
||||
.Tn SYN-SENT
|
||||
state.
|
||||
.It tcp.do_tcpdrain
|
||||
.It Va do_tcpdrain
|
||||
Flush packets in the
|
||||
.Tn TCP
|
||||
reassembly queue if the system is low on mbufs.
|
||||
.It tcp.blackhole
|
||||
.It Va blackhole
|
||||
If enabled, disable sending of RST when a connection is attempted
|
||||
to a port where there is not a socket accepting connections.
|
||||
See
|
||||
.Xr blackhole 4 .
|
||||
.It tcp.delayed_ack
|
||||
.It Va delayed_ack
|
||||
Delay ACK to try and piggyback it onto a data packet.
|
||||
.It tcp.delacktime
|
||||
.It Va delacktime
|
||||
Maximum amount of time, in milliseconds, before a delayed ACK is sent.
|
||||
.It tcp.newreno
|
||||
Enable TCP NewReno Fast Recovery algorithm,
|
||||
.It Va newreno
|
||||
Enable
|
||||
.Tn TCP
|
||||
NewReno Fast Recovery algorithm,
|
||||
as described in RFC 2582.
|
||||
.It tcp.path_mtu_discovery
|
||||
Enable Path MTU Discovery
|
||||
.It tcp.tcbhashsize
|
||||
.It Va path_mtu_discovery
|
||||
Enable Path MTU Discovery.
|
||||
.It Va tcbhashsize
|
||||
Size of the
|
||||
.Tn TCP
|
||||
control-block hashtable
|
||||
control-block hash table
|
||||
(read-only).
|
||||
This may be tuned using the kernel option
|
||||
.Dv TCBHASHSIZE
|
||||
@ -285,14 +308,22 @@ or by setting
|
||||
.Va net.inet.tcp.tcbhashsize
|
||||
in the
|
||||
.Xr loader 8 .
|
||||
.It tcp.pcbcount
|
||||
.It Va pcbcount
|
||||
Number of active process control blocks
|
||||
(read-only).
|
||||
.It tcp.syncookies
|
||||
Determines whether or not syn cookies should be generated for
|
||||
outbound syn-ack packets. Syn cookies are a great help during
|
||||
syn flood attacks, and are enabled by default.
|
||||
.It tcp.isn_reseed_interval
|
||||
.It Va syncookies
|
||||
Determines whether or not
|
||||
.Tn SYN
|
||||
cookies should be generated for outbound
|
||||
.Tn SYN-ACK
|
||||
packets.
|
||||
.Tn SYN
|
||||
cookies are a great help during
|
||||
.Tn SYN
|
||||
flood attacks, and are enabled by default.
|
||||
(See
|
||||
.Xr syncookies 4 . )
|
||||
.It Va isn_reseed_interval
|
||||
The interval (in seconds) specifying how often the secret data used in
|
||||
RFC 1948 initial sequence number calculations should be reseeded.
|
||||
By default, this variable is set to zero, indicating that
|
||||
@ -300,84 +331,120 @@ no reseeding will occur.
|
||||
Reseeding should not be necessary, and will break
|
||||
.Dv TIME_WAIT
|
||||
recycling for a few minutes.
|
||||
.It tcp.inet.tcp.rexmit_{min,slop}
|
||||
Adjust the retransmit timer calculation for TCP. The slop is
|
||||
.It Va rexmit_min , rexmit_slop
|
||||
Adjust the retransmit timer calculation for
|
||||
.Tn TCP .
|
||||
The slop is
|
||||
typically added to the raw calculation to take into account
|
||||
occasional variances that the SRTT (smoothed round trip time)
|
||||
occasional variances that the
|
||||
.Tn SRTT
|
||||
(smoothed round-trip time)
|
||||
is unable to accomodate, while the minimum specifies an
|
||||
absolute minimum. While a number of TCP RFCs suggest a 1
|
||||
second minimum these RFCs tend to focus on streaming behavior
|
||||
absolute minimum.
|
||||
While a number of
|
||||
.Tn TCP
|
||||
RFCs suggest a 1
|
||||
second minimum, these RFCs tend to focus on streaming behavior,
|
||||
and fail to deal with the fact that a 1 second minimum has severe
|
||||
detrimental effects over lossy interactive connections, such
|
||||
as a 802.11b wireless link, and over very fast but lossy
|
||||
connections for those cases not covered by the fast retransmit
|
||||
code. For this reason we use 200ms of slop and a near-0
|
||||
minimum, which gives us an effective minimum of 200ms (similar to Linux).
|
||||
.It tcp.inflight_enable
|
||||
code.
|
||||
For this reason, we use 200ms of slop and a near-0
|
||||
minimum, which gives us an effective minimum of 200ms (similar to
|
||||
.Tn Linux ) .
|
||||
.It Va inflight_enable
|
||||
Enable
|
||||
.Tn TCP
|
||||
bandwidth delay product limiting. An attempt will be made to calculate
|
||||
the bandwidth delay product for each individual TCP connection and limit
|
||||
the amount of inflight data being transmitted to avoid building up
|
||||
unnecessary packets in the network. This option is recommended if you
|
||||
bandwidth-delay product limiting.
|
||||
An attempt will be made to calculate
|
||||
the bandwidth-delay product for each individual
|
||||
.Tn TCP
|
||||
connection, and limit
|
||||
the amount of inflight data being transmitted, to avoid building up
|
||||
unnecessary packets in the network.
|
||||
This option is recommended if you
|
||||
are serving a lot of data over connections with high bandwidth-delay
|
||||
products, such as modems, GigE links, and fast long-haul WANs, and/or
|
||||
you have configured your machine to accomodate large TCP windows. In such
|
||||
you have configured your machine to accomodate large
|
||||
.Tn TCP
|
||||
windows.
|
||||
In such
|
||||
situations, without this option, you may experience high interactive
|
||||
latencies or packet loss due to the overloading of intermediate routers
|
||||
and switches. Note that bandwidth delay product limiting only effects
|
||||
the transmit side of a TCP connection.
|
||||
.It tcp.inflight_debug
|
||||
Enable debugging for the bandwidth delay product algorithm. This may
|
||||
default to on (1) so if you enable the algorithm you should probably also
|
||||
and switches.
|
||||
Note that bandwidth-delay product limiting only effects
|
||||
the transmit side of a
|
||||
.Tn TCP
|
||||
connection.
|
||||
.It Va inflight_debug
|
||||
Enable debugging for the bandwidth-delay product algorithm.
|
||||
This may
|
||||
default to on (1), so if you enable the algorithm,
|
||||
you should probably also
|
||||
disable debugging by setting this variable to 0.
|
||||
.It tcp.inflight_min
|
||||
This puts a lower bound on the bandwidth delay product window, in bytes.
|
||||
A value of 1024 is typically used for debugging. 6000-16000 is more typical
|
||||
in a production installation. Setting this value too low may result in
|
||||
slow ramp-up times for bursty connections. Setting this value too high
|
||||
effectively disables the algorithm.
|
||||
.It tcp.inflight_max
|
||||
This puts an upper bound on the bandwidth delay product window, in bytes.
|
||||
This value should not generally be modified but may be used to set a
|
||||
.It Va inflight_min
|
||||
This puts a lower bound on the bandwidth-delay product window, in bytes.
|
||||
A value of 1024 is typically used for debugging.
|
||||
6000-16000 is more typical in a production installation.
|
||||
Setting this value too low may result in
|
||||
slow ramp-up times for bursty connections.
|
||||
Setting this value too high effectively disables the algorithm.
|
||||
.It Va inflight_max
|
||||
This puts an upper bound on the bandwidth-delay product window, in bytes.
|
||||
This value should not generally be modified, but may be used to set a
|
||||
global per-connection limit on queued data, potentially allowing you to
|
||||
intentionally set a less than optimum limit to smooth data flow over a
|
||||
network while still being able to specify huge internal TCP buffers.
|
||||
.It tcp.inflight_stab
|
||||
The bandwidth delay product algorithm requires a slightly larger window
|
||||
than it otherwise calculates for stability. This parameter determines the
|
||||
extra window in maximal packets / 10. The default value of 20 represents
|
||||
2 maximal packets. Reducing this value is not recommended but you may
|
||||
come across a situation with very slow links where the ping time
|
||||
reduction of the default inflight code is not sufficient. If this case
|
||||
occurs, you should first try reducing
|
||||
.Va tcp.inflight_min
|
||||
intentionally set a less than optimum limit, to smooth data flow over a
|
||||
network while still being able to specify huge internal
|
||||
.Tn TCP
|
||||
buffers.
|
||||
.It Va inflight_stab
|
||||
The bandwidth-delay product algorithm requires a slightly larger window
|
||||
than it otherwise calculates for stability.
|
||||
This parameter determines the extra window in maximal packets / 10.
|
||||
The default value of 20 represents 2 maximal packets.
|
||||
Reducing this value is not recommended, but you may
|
||||
come across a situation with very slow links where the
|
||||
.Xr ping 8
|
||||
time
|
||||
reduction of the default inflight code is not sufficient.
|
||||
If this case occurs, you should first try reducing
|
||||
.Va inflight_min
|
||||
and, if that does not
|
||||
work, reduce both
|
||||
.Va tcp.inflight_min
|
||||
.Va inflight_min
|
||||
and
|
||||
.Va tcp.inflight_stab ,
|
||||
.Va inflight_stab ,
|
||||
trying values of
|
||||
15, 10, or 5 for the latter. Never use a value less than 5. Reducing
|
||||
.Va tcp.inflight_stab
|
||||
15, 10, or 5 for the latter.
|
||||
Never use a value less than 5.
|
||||
Reducing
|
||||
.Va inflight_stab
|
||||
can lead to upwards of a 20% underutilization of the link
|
||||
as well as reducing the algorithm's ability to adapt to changing
|
||||
situations and should only be done as a last resort.
|
||||
.It tcp.rfc3042
|
||||
Enable the Limited Transmit algorithm as described in RFC 3042. It
|
||||
.It Va rfc3042
|
||||
Enable the Limited Transmit algorithm as described in RFC 3042.
|
||||
It
|
||||
helps avoid timeouts on lossy links and also when the congestion window
|
||||
is small, as happens on short transfers. This is a standards track RFC
|
||||
is small, as happens on short transfers.
|
||||
This is a standards track RFC
|
||||
and is off by default.
|
||||
.It tcp.rfc3390
|
||||
.It Va rfc3390
|
||||
Enable support for RFC 3390, which allows for a variable-sized
|
||||
starting congestion window on new connections, depending on the
|
||||
maximum segment size. This helps throughput in general, but
|
||||
maximum segment size.
|
||||
This helps throughput in general, but
|
||||
particularly affects short transfers and high-bandwidth large
|
||||
propagation-delay connections. This is a standards track RFC and
|
||||
propagation-delay connections.
|
||||
This is a standards track RFC and
|
||||
support for it is off by default.
|
||||
.Pp
|
||||
When this feature is enabled, the slowstart_flightsize and
|
||||
local_slowstart_flightsize settings are not observed for new
|
||||
When this feature is enabled, the
|
||||
.Va slowstart_flightsize
|
||||
and
|
||||
.Va local_slowstart_flightsize
|
||||
settings are not observed for new
|
||||
connection slow starts, but they are still used for slow starts
|
||||
that occur when the connection has been idle and starts sending
|
||||
again.
|
||||
@ -408,7 +475,7 @@ allocated;
|
||||
.It Bq Er EADDRNOTAVAIL
|
||||
when an attempt is made to create a
|
||||
socket with a network address for which no network interface
|
||||
exists.
|
||||
exists;
|
||||
.It Bq Er EAFNOSUPPORT
|
||||
when an attempt is made to bind or connect a socket to a multicast
|
||||
address.
|
||||
@ -424,20 +491,20 @@ address.
|
||||
.Xr syncache 4 ,
|
||||
.Xr ttcp 4
|
||||
.Rs
|
||||
.%A V. Jacobson
|
||||
.%A R. Braden
|
||||
.%A D. Borman
|
||||
.%A "V. Jacobson"
|
||||
.%A "R. Braden"
|
||||
.%A "D. Borman"
|
||||
.%T "TCP Extensions for High Performance"
|
||||
.%O RFC 1323
|
||||
.%O "RFC 1323"
|
||||
.Re
|
||||
.Rs
|
||||
.%A R. Braden
|
||||
.%A "R. Braden"
|
||||
.%T "T/TCP \- TCP Extensions for Transactions"
|
||||
.%O RFC 1644
|
||||
.%O "RFC 1644"
|
||||
.Re
|
||||
.Sh HISTORY
|
||||
The
|
||||
.Nm
|
||||
.Tn TCP
|
||||
protocol appeared in
|
||||
.Bx 4.2 .
|
||||
The RFC 1323 extensions for window scaling and timestamps were added
|
||||
|
||||
Loading…
Reference in New Issue
Block a user