git: 3dce6f96e515 - main - tcp.4: Add missing sysctls, other fixes
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Date: Tue, 02 Aug 2022 14:51:12 UTC
The branch main has been updated by karels:
URL: https://cgit.FreeBSD.org/src/commit/?id=3dce6f96e515245f8fb6c540df07af1af838ab89
commit 3dce6f96e515245f8fb6c540df07af1af838ab89
Author: Mike Karels <karels@FreeBSD.org>
AuthorDate: 2022-07-31 18:57:03 +0000
Commit: Mike Karels <karels@FreeBSD.org>
CommitDate: 2022-08-02 14:51:03 +0000
tcp.4: Add missing sysctls, other fixes
Add some of the missing sysctls to tcp.4, using references to other
man pages where they exist. Added sysctls include recvbuf and sendbuf
controls for automatic buffer sizing. Updated recvspace and sendspace.
Add sysctl.8 to "see also" and intro to variable section. Rename
"MIB Variables" section to "MIB (sysctl) Variables", as most people
will associate with sysctl.
Reviewed by: manpages(pauamma), tuexen
Differential Revision: https://reviews.freebsd.org/D36004
---
share/man/man4/tcp.4 | 98 ++++++++++++++++++++++++++++++++++++++++++----------
1 file changed, 80 insertions(+), 18 deletions(-)
diff --git a/share/man/man4/tcp.4 b/share/man/man4/tcp.4
index 483984112031..cdb58c7cbacc 100644
--- a/share/man/man4/tcp.4
+++ b/share/man/man4/tcp.4
@@ -34,7 +34,7 @@
.\" From: @(#)tcp.4 8.1 (Berkeley) 6/5/93
.\" $FreeBSD$
.\"
-.Dd July 20, 2022
+.Dd August 1, 2022
.Dt TCP 4
.Os
.Sh NAME
@@ -203,12 +203,12 @@ The alternate TCP stack must already be loaded in the kernel.
To list the available TCP stacks, see
.Va functions_available
in the
-.Sx MIB Variables
+.Sx MIB (sysctl) Variables
section further down.
To list the default TCP stack, see
.Va functions_default
in the
-.Sx MIB Variables
+.Sx MIB (sysctl) Variables
section.
.It Dv TCP_KEEPINIT
This
@@ -221,7 +221,7 @@ connections.
For the global default in milliseconds see
.Va keepinit
in the
-.Sx MIB Variables
+.Sx MIB (sysctl) Variables
section further down.
.It Dv TCP_KEEPIDLE
This
@@ -237,7 +237,7 @@ socket upon
For the global default in milliseconds see
.Va keepidle
in the
-.Sx MIB Variables
+.Sx MIB (sysctl) Variables
section further down.
.It Dv TCP_KEEPINTVL
This
@@ -252,7 +252,7 @@ socket upon
For the global default in milliseconds see
.Va keepintvl
in the
-.Sx MIB Variables
+.Sx MIB (sysctl) Variables
section further down.
.It Dv TCP_KEEPCNT
This
@@ -267,7 +267,7 @@ socket upon
For the global default see the
.Va keepcnt
in the
-.Sx MIB Variables
+.Sx MIB (sysctl) Variables
section further down.
.It Dv TCP_NODELAY
Under most circumstances,
@@ -413,14 +413,15 @@ is
Other congestion control algorithms can be made available using the
.Xr mod_cc 4
framework.
-.Ss MIB Variables
+.Ss MIB (sysctl) Variables
The
.Tn TCP
protocol implements a number of variables in the
.Va net.inet.tcp
branch of the
.Xr sysctl 3
-MIB.
+MIB, which can also be read or modified with
+.Xr sysctl 8 .
.Bl -tag -width ".Va v6pmtud_blackhole_mss"
.It Va always_keepalive
Assume that
@@ -432,13 +433,28 @@ periodically send a packet to the remote host to verify the connection
is still up.
.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.
+to a port where there is no socket accepting connections.
See
.Xr blackhole 4 .
+.It Va blackhole_local
+See
+.Xr blackhole 4 .
+.It Va cc
+A number of variables for congestion control are under the
+.Va net.inet.tcp.cc
+node.
+See
+.Xr mod_cc 4 .
+.It Va cc.newreno
+Variables for NewReno congestion control are under the
+.Va net.inet.tcp.cc.newreno
+node.
+See
+.Xr cc_newreno 4 .
.It Va delacktime
Maximum amount of time, in milliseconds, before a delayed ACK is sent.
.It Va delayed_ack
-Delay ACK to try and piggyback it onto a data packet.
+Delay ACK to try and piggyback it onto a data packet or another ACK.
.It Va do_lrd
Enable Lost Retransmission Detection for SACK-enabled sessions, disabled by
default.
@@ -463,6 +479,8 @@ high losses leading to RTO, but reduces PRR effectiveness in more common setting
Flush packets in the
.Tn TCP
reassembly queue if the system is low on mbufs.
+.It Va drop_synfin
+Drop TCP packets with both SYN and FIN set.
.It Va ecn.enable
Enable support for TCP Explicit Congestion Notification (ECN).
ECN allows a TCP sender to reduce the transmission rate in order to
@@ -706,7 +724,7 @@ machines, when no response is received on a
probe.
The default is 75000 msec (75K msec, 75 sec).
.It Va log_in_vain
-Log any connection attempts to ports where there is not a socket
+Log any connection attempts to ports where there is no socket
accepting connections.
The value of 1 limits the logging to
.Tn SYN
@@ -733,12 +751,15 @@ MIB variable controls the maximum number of these structures allocated.
By default, it is initialized to
.Va kern.ipc.maxsockets
/ 5.
+.It Va minmss
+Minimum TCP Maximum Segment Size; used to prevent a denial of service attack
+from an unreasonably low MSS.
.It Va msl
The Maximum Segment Lifetime, in milliseconds, for a packet.
.It Va mssdflt
-The default value used for the maximum segment size
+The default value used for the TCP Maximum Segment Size
.Pq Dq MSS
-when no advice to the contrary is received from MSS negotiation.
+for IPv4 when no advice to the contrary is received from MSS negotiation.
.It Va newcwd
Enable the New Congestion Window Validation mechanism as described in RFC 7661.
This gently reduces the congestion window during periods, where TCP is
@@ -766,6 +787,10 @@ A CSV list of template_spec=percent key-value pairs which controls the per
template sampling rates when
.Xr stats 3
sampling is enabled.
+.It Va persmax
+Maximum persistence interval, msec.
+.It Va persmin
+Minimum persistence interval, msec.
.It Va pmtud_blackhole_detection
Enable automatic path MTU blackhole detection.
In case of retransmits of MSS sized segments,
@@ -808,10 +833,21 @@ limit.
The maximum limit on the total number of segments across all reassembly
queues.
The limit can be adjusted as a tunable.
+.It Va recvbuf_auto
+Enable automatic receive buffer sizing as a connection progresses.
+.It Va recvbuf_max
+Maximum size of automatic receive buffer.
.It Va recvspace
-Maximum
+Initial
.Tn TCP
-receive window.
+receive window (buffer size).
+.It Va require_unique_port
+Require unique ephemeral port for outgoing connections;
+otherwise, the 4-tuple of local and remote ports and addresses must be unique.
+Requiring a unique port limits the number of outgoing connections.
+.It Va rexmit_drop_options
+Drop TCP options from third and later retransmitted SYN segments
+of a connection.
.It Va rexmit_initial , rexmit_min , rexmit_slop
Adjust the retransmit timer calculation for
.Tn TCP .
@@ -857,6 +893,8 @@ Enable support for RFC 2018, TCP Selective Acknowledgment option,
which allows the receiver to inform the sender about all successfully
arrived segments, allowing the sender to retransmit the missing segments
only.
+.It Va sack.globalholes
+Global number of TCP SACK holes currently allocated.
.It Va sack.globalmaxholes
Maximum number of SACK holes per system, across all connections.
Defaults to 65536.
@@ -874,10 +912,24 @@ recovery, the trailing segment is immediately resent, rather than waiting
for a Retransmission timeout.
Finally, SACK loss recovery is also engaged, once two segments plus one byte are
SACKed - even if no traditional duplicate ACKs were observed.
+.It Va sendbuf_auto
+Enable automatic send buffer sizing.
+.It Va sendbuf_auto_lowat
+Modify threshold for auto send buffer growth to account for
+.Dv SO_SNDLOWAT .
+.It Va sendbuf_inc
+Incrementor step size of automatic send buffer.
+.It Va sendbuf_max
+Maximum size of automatic send buffer.
.It Va sendspace
-Maximum
+Initial
.Tn TCP
-send window.
+send window (buffer size).
+.It Va syncache
+Variables under the
+.Va net.inet.tcp.syncache
+node are documented in
+.Xr syncache 4 .
.It Va syncookies
Determines whether or not
.Tn SYN
@@ -890,6 +942,9 @@ cookies are a great help during
flood attacks, and are enabled by default.
(See
.Xr syncookies 4 . )
+.It Va syncookies_only
+See
+.Xr syncookies 4 .
.It Va tcbhashsize
Size of the
.Tn TCP
@@ -916,6 +971,8 @@ Therefore the default is 1, i.e., the missing of timestamps is tolerated.
When initializing the TCP timestamps, use a per connection offset instead of a
per host pair offset.
Default is to use per connection offsets as recommended in RFC 7323.
+.It Va tso
+Enable TCP Segmentation Offload.
.It Va udp_tunneling_overhead
The overhead taken into account when using UDP encapsulation.
Since MSS clamping by middleboxes will most likely not work, values larger than
@@ -926,6 +983,10 @@ The default is 8.
The local UDP encapsulation port.
A value of 0 indicates that UDP encapsulation is disabled.
The default is 0.
+.It Va v6mssdflt
+The default value used for the TCP Maximum Segment Size
+.Pq Dq MSS
+for IPv6 when no advice to the contrary is received from MSS negotiation.
.It Va v6pmtud_blackhole_mss
MSS to try for IPv6 if PMTU blackhole detection is turned on.
See
@@ -981,6 +1042,7 @@ when trying to use a TCP function block that is not available;
.Xr syncache 4 ,
.Xr tcp_bbr 4 ,
.Xr setkey 8 ,
+.Xr sysctl 8 ,
.Xr tcp_functions 9
.Rs
.%A "V. Jacobson"