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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | |||||||||
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY | .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY | |||||||||
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | |||||||||
.\" SUCH DAMAGE. | .\" SUCH DAMAGE. | |||||||||
.\" | .\" | |||||||||
.\" From: @(#)tcp.4 8.1 (Berkeley) 6/5/93 | .\" From: @(#)tcp.4 8.1 (Berkeley) 6/5/93 | |||||||||
.\" $FreeBSD$ | .\" $FreeBSD$ | |||||||||
.\" | .\" | |||||||||
.Dd January 14, 2021 | .Dd February 8, 2021 | |||||||||
.Dt TCP 4 | .Dt TCP 4 | |||||||||
.Os | .Os | |||||||||
.Sh NAME | .Sh NAME | |||||||||
.Nm tcp | .Nm tcp | |||||||||
.Nd Internet Transmission Control Protocol | .Nd Internet Transmission Control Protocol | |||||||||
.Sh SYNOPSIS | .Sh SYNOPSIS | |||||||||
.In sys/types.h | .In sys/types.h | |||||||||
.In sys/socket.h | .In sys/socket.h | |||||||||
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.It Va delayed_ack | .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. | |||||||||
.It Va delacktime | .It Va delacktime | |||||||||
Maximum amount of time, in milliseconds, before a delayed ACK is sent. | Maximum amount of time, in milliseconds, before a delayed ACK is sent. | |||||||||
.It Va path_mtu_discovery | .It Va path_mtu_discovery | |||||||||
Enable Path MTU Discovery. | Enable Path MTU Discovery. | |||||||||
.It Va tcbhashsize | .It Va tcbhashsize | |||||||||
Size of the | Size of the | |||||||||
.Tn TCP | .Tn TCP | |||||||||
control-block hash table | control-block hash table | |||||||||
pauamma_gundo.comUnsubmitted Done Inline Actions
pauamma_gundo.com: | ||||||||||
(read-only). | (read-only). | |||||||||
This may be tuned using the kernel option | This may be tuned using the kernel option | |||||||||
.Dv TCBHASHSIZE | .Dv TCBHASHSIZE | |||||||||
or by setting | or by setting | |||||||||
.Va net.inet.tcp.tcbhashsize | .Va net.inet.tcp.tcbhashsize | |||||||||
in the | in the | |||||||||
.Xr loader 8 . | .Xr loader 8 . | |||||||||
.It Va pcbcount | .It Va pcbcount | |||||||||
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.Xr syncookies 4 . ) | .Xr syncookies 4 . ) | |||||||||
.It Va isn_reseed_interval | .It Va isn_reseed_interval | |||||||||
The interval (in seconds) specifying how often the secret data used in | The interval (in seconds) specifying how often the secret data used in | |||||||||
RFC 1948 initial sequence number calculations should be reseeded. | RFC 1948 initial sequence number calculations should be reseeded. | |||||||||
By default, this variable is set to zero, indicating that | By default, this variable is set to zero, indicating that | |||||||||
no reseeding will occur. | no reseeding will occur. | |||||||||
Reseeding should not be necessary, and will break | Reseeding should not be necessary, and will break | |||||||||
.Dv TIME_WAIT | .Dv TIME_WAIT | |||||||||
recycling for a few minutes. | recycling for a few minutes. | |||||||||
.It Va reass.cursegments | .It Va reass.cursegments | |||||||||
Done Inline ActionsWas removing this intended as part of this review? pauamma_gundo.com: Was removing this intended as part of this review? | ||||||||||
Done Inline ActionsI'm confused, there is no change here on reviews.freebsd.org; it may be that this diff was uploaded just prior to a flurry of tcp related (including man page) changes, which I have not yet rebased the patch to... rscheff: I'm confused, there is no change here on reviews.freebsd.org; it may be that this diff was… | ||||||||||
The current total number of segments present in all reassembly queues. | The current total number of segments present in all reassembly queues. | |||||||||
.It Va reass.maxsegments | .It Va reass.maxsegments | |||||||||
The maximum limit on the total number of segments across all reassembly | The maximum limit on the total number of segments across all reassembly | |||||||||
queues. | queues. | |||||||||
The limit can be adjusted as a tunable. | The limit can be adjusted as a tunable. | |||||||||
.It Va reass.maxqueuelen | .It Va reass.maxqueuelen | |||||||||
The maximum number of segments allowed in each reassembly queue. | The maximum number of segments allowed in each reassembly queue. | |||||||||
By default, the system chooses a limit based on each TCP connection's | By default, the system chooses a limit based on each TCP connection's | |||||||||
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Allow incoming connections to request ECN. | Allow incoming connections to request ECN. | |||||||||
Outgoing connections will not request ECN. | Outgoing connections will not request ECN. | |||||||||
.El | .El | |||||||||
.It Va ecn.maxretries | .It Va ecn.maxretries | |||||||||
Number of retries (SYN or SYN/ACK retransmits) before disabling ECN on a | Number of retries (SYN or SYN/ACK retransmits) before disabling ECN on a | |||||||||
specific connection. | specific connection. | |||||||||
This is needed to help with connection establishment | This is needed to help with connection establishment | |||||||||
when a broken firewall is in the network path. | when a broken firewall is in the network path. | |||||||||
.It Va ecn.generalized | ||||||||||
Enable sending all segments as ECN capable transport, | ||||||||||
including SYN, SYN/ACK, and retransmissions. | ||||||||||
This may only be enabled, when ECN support itself is also active. | ||||||||||
Done Inline Actions
pauamma_gundo.com: | ||||||||||
Disabling ECN support will disable this feature automatically. | ||||||||||
Settings: | ||||||||||
.Bl -tag -compact | ||||||||||
.It 0 | ||||||||||
Regular RFC3168 operation. Send only new data segements as ECN capable | ||||||||||
transport. | ||||||||||
.It 1 | ||||||||||
Done Inline Actions
Typo and move full stop to a more natural place. pauamma_gundo.com: Typo and move full stop to a more natural place. | ||||||||||
Support generalized ECN (ECN++), and send all segments of an ECN-enabled | ||||||||||
session as ECN capable transport. | ||||||||||
Also control packets to non-established and non-listening ports are | ||||||||||
identially marked. | ||||||||||
.El | ||||||||||
Done Inline Actionss/identially/identically/ bcr: s/identially/identically/ | ||||||||||
Done Inline ActionsCan you explain what you mean by that? I'm arguably not the indended audience, but if I don't understand it, there's a chance some of the intended audience and or some interested readers won't either. pauamma_gundo.com: Can you explain what you mean by that? I'm arguably not the indended audience, but if I don't… | ||||||||||
Done Inline ActionsWhen a host receives a TCP packet to a port which is not listening, or no connection exists, or the header information is in some other way not acceptable, the host may respond with a RST (reset) packet. Some of these RST packets are sent from "regular" TCP processing (e.g. outside the sequence window) and others from non-open ports. Making these distinctable by carrying different markings - depending which code path was sending them - would give clues as to what ports/services may be reachable, and give rise to more targetted attacks. rscheff: When a host receives a TCP packet to a port which is not listening, or no connection exists, or… | ||||||||||
Done Inline ActionsGotcha, thanks. Would "This value also uses ECN for RST replies to probes of non-open ports." mean the same? It looks clearer to me. pauamma_gundo.com: Gotcha, thanks. Would "This value also uses ECN for RST replies to probes of non-open ports."… | ||||||||||
.It Va pmtud_blackhole_detection | .It Va pmtud_blackhole_detection | |||||||||
Enable automatic path MTU blackhole detection. | Enable automatic path MTU blackhole detection. | |||||||||
In case of retransmits of MSS sized segments, | In case of retransmits of MSS sized segments, | |||||||||
the OS will lower the MSS to check if it's an MTU problem. | the OS will lower the MSS to check if it's an MTU problem. | |||||||||
If the current MSS is greater than the configured value to try | If the current MSS is greater than the configured value to try | |||||||||
.Po Va net.inet.tcp.pmtud_blackhole_mss | .Po Va net.inet.tcp.pmtud_blackhole_mss | |||||||||
and | and | |||||||||
.Va net.inet.tcp.v6pmtud_blackhole_mss | .Va net.inet.tcp.v6pmtud_blackhole_mss | |||||||||
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