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zephyr/subsys/net/ip/Kconfig.tcp
Robert Lubos f211cd6345 net: tcp: Deprecate CONFIG_NET_TCP_ACK_TIMEOUT 
Deprecate CONFIG_NET_TCP_ACK_TIMEOUT as it is redundant with the
combination of CONFIG_NET_TCP_INIT_RETRANSMISSION_TIMEOUT and
CONFIG_NET_TCP_RETRY_COUNT. The total retransmission timeout (i. e.
waiting for ACK) should depend on the individual retransmission timeout
and retry count, having separate config is simply ambiguous and
confusing for users.

Moreover, the config was currently only used during TCP handshake, and
for that purpose we could use the very same timeout that is used for the
FIN timeout. Therefore, repurpose the fin_timeout_ms to be a generic,
maximum timeout at the TCP stack.

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>
2024-04-03 15:32:45 -04:00

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# TCP options
# Copyright (c) 2016 Intel Corporation.
# Copyright (c) 2021 Nordic Semiconductor
# Copyright (c) 2023 Arm Limited (or its affiliates). All rights reserved.
# SPDX-License-Identifier: Apache-2.0
menuconfig NET_TCP
bool "TCP"
depends on NET_IP
help
The value depends on your network needs.
if NET_TCP
if NET_TCP
module = NET_TCP
module-dep = NET_LOG
module-str = Log level for TCP
module-help = Enables TCP handler output debug messages
source "subsys/net/Kconfig.template.log_config.net"
endif # NET_TCP
config NET_TCP_WORKQ_STACK_SIZE
int "TCP work queue thread stack size"
default 1200 if X86
default 1024
depends on NET_TCP
help
Set the TCP work queue thread stack size in bytes.
config NET_TCP_WORKER_PRIO
int "Priority of the TCP work queue"
default 2
depends on NET_TCP
help
Set the priority of the TCP worker queue, that handles all
transmission and maintenance within the TCP stack.
Value 0 = highest priortity.
When CONFIG_NET_TC_THREAD_COOPERATIVE = y, lowest priority is
CONFIG_NUM_COOP_PRIORITIES-1 else lowest priority is
CONFIG_NUM_PREEMPT_PRIORITIES-1.
Make sure the priority is lower than lower layer TX threads to
avoid the TCP stack consume all net_bufs before transferring
execution to the lower layer network stack, with a high risk of
running out of net_bufs.
config NET_TCP_TIME_WAIT_DELAY
int "How long to wait in TIME_WAIT state (in milliseconds)"
depends on NET_TCP
default 1500
help
To avoid a (low-probability) issue when delayed packets from
previous connection get delivered to next connection reusing
the same local/remote ports, RFC 793 (TCP) suggests to keep
an old, closed connection in a special "TIME_WAIT" state for
the duration of 2*MSL (Maximum Segment Lifetime). The RFC
suggests to use MSL of 2 minutes, but notes "This is an
engineering choice, and may be changed if experience indicates
it is desirable to do so." For low-resource systems, having
large MSL may lead to quick resource exhaustion (and related
DoS attacks). At the same time, the issue of packet misdelivery
is largely alleviated in the modern TCP stacks by using random,
non-repeating port numbers and initial sequence numbers. Due
to this, Zephyr uses much lower value of 1500ms by default.
Value of 0 disables TIME_WAIT state completely.
config NET_TCP_ACK_TIMEOUT
int "[DEPRECATED] How long to wait for ACK (in milliseconds)"
depends on NET_TCP
default 1000
range 1 2147483647
help
Deprecated. Use CONFIG_NET_TCP_INIT_RETRANSMISSION_TIMEOUT and
CONFIG_NET_TCP_RETRY_COUNT to control the total timeout at the TCP
level.
config NET_TCP_INIT_RETRANSMISSION_TIMEOUT
int "Initial value of Retransmission Timeout (RTO) (in milliseconds)"
depends on NET_TCP
default 200
range 100 60000
help
This value affects the timeout between initial retransmission
of TCP data packets. The value is in milliseconds.
config NET_TCP_RANDOMIZED_RTO
bool "Use a randomized retransmission time"
default y
depends on NET_TCP
help
It can happen that two similar stacks enter a retransmission cycle
due to a packet collision. If the transmission timeout is the same
both stacks will retry at the same moment resulting in another
collision. By introducing a randomized retry timeout, the chance of
a second collision is reduced and it reduces furter the more
retransmissions occur.
config NET_TCP_RETRY_COUNT
int "Maximum number of TCP segment retransmissions"
depends on NET_TCP
default 9
help
The following formula can be used to determine the time (in ms)
that a segment will be be buffered awaiting retransmission:
n=NET_TCP_RETRY_COUNT
Sum((1<<n) * NET_TCP_INIT_RETRANSMISSION_TIMEOUT)
n=0
With the default value of 9, the IP stack will try to
retransmit for up to 1:42 minutes. This is as close as possible
to the minimum value recommended by RFC1122 (1:40 minutes).
Only 5 bits are dedicated for the retransmission count, so accepted
values are in the 0-31 range. It's highly recommended to not go
below 9, though.
Should a retransmission timeout occur, the receive callback is
called with -ETIMEDOUT error code and the context is dereferenced.
config NET_TCP_MAX_SEND_WINDOW_SIZE
int "Maximum sending window size to use"
depends on NET_TCP
default 0
range 0 65535
help
This value affects how the TCP selects the maximum sending window
size. The default value 0 lets the TCP stack select the value
according to amount of network buffers configured in the system.
config NET_TCP_MAX_RECV_WINDOW_SIZE
int "Maximum receive window size to use"
depends on NET_TCP
default 0
range 0 65535
help
This value defines the maximum TCP receive window size. Increasing
this value can improve connection throughput, but requires more
receive buffers available in the system for efficient operation.
The default value 0 lets the TCP stack select the value
according to amount of network buffers configured in the system.
config NET_TCP_RECV_QUEUE_TIMEOUT
int "How long to queue received data (in ms)"
depends on NET_TCP
default 2000
range 0 10000
help
If we receive out-of-order TCP data, we queue it. This value tells
how long the data is kept before it is discarded if we have not been
able to pass the data to the application. If set to 0, then receive
queueing is not enabled. The value is in milliseconds.
Note that we only queue data sequentially in current version i.e.,
there should be no holes in the queue. For example, if we receive
SEQs 5,4,3,6 and are waiting SEQ 2, the data in segments 3,4,5,6 is
queued (in this order), and then given to application when we receive
SEQ 2. But if we receive SEQs 5,4,3,7 then the SEQ 7 is discarded
because the list would not be sequential as number 6 is be missing.
config NET_TCP_PKT_ALLOC_TIMEOUT
int "How long to wait for a TCP packet allocation (in ms)"
depends on NET_TCP
default 100
range 10 1000
help
The TCP network stack allocates packets from the buffers and the
allocation can take some time depending on the situation.
This value indicates how long the stack should wait for the packet to
be allocated, before returning an internal error and trying again.
config NET_TCP_CHECKSUM
bool "Check TCP checksum"
default y
depends on NET_TCP
help
Enables TCP handler to check TCP checksum. If the checksum is invalid,
then the packet is discarded.
config NET_TCP_FAST_RETRANSMIT
bool "Fast-retry algorithm based on the number of duplicated ACKs"
depends on NET_TCP
default y
help
When a packet is lost, the receiver will keep acknowledging the
sequence number of the last correctly received byte. Upon reception
of a sequence of acknowledgements for the same sequence number,
this can be deduced as that the packet afterwards must have been lost.
In that case a retransmission is triggered to avoid having to wait for
the retransmit timer to elapse.
config NET_TCP_CONGESTION_AVOIDANCE
bool "Implement a congestion avoidance algorithm in TCP"
depends on NET_TCP
default y
help
To avoid overstressing a link reduce the transmission rate as soon as
packets are starting to drop.
config NET_TCP_KEEPALIVE
bool "TCP keep-alive support"
depends on NET_TCP
help
Enabling this option allows the TCP stack to send periodic TCP
keep-alive probes. Enables SO_KEEPALIVE, TCP_KEEPIDLE, TCP_KEEPINTVL
and TCP_KEEPCNT options processing.
config NET_TCP_KEEPIDLE_DEFAULT
int "TCP_KEEPIDLE default value"
depends on NET_TCP_KEEPALIVE
default 7200
help
The time (in seconds) the connection needs to remain idle before TCP
starts sending keepalive probes, if the socket option SO_KEEPALIVE has
been set on this socket.
config NET_TCP_KEEPINTVL_DEFAULT
int "TCP_KEEPINTVL default value"
depends on NET_TCP_KEEPALIVE
default 75
help
The time (in seconds) between individual keepalive probes.
config NET_TCP_KEEPCNT_DEFAULT
int "TCP_KEEPCNT default value"
depends on NET_TCP_KEEPALIVE
default 9
help
The maximum number of keepalive probes TCP should send before dropping
the connection.
config NET_TCP_ISN_RFC6528
bool "Use ISN algorithm from RFC 6528"
default y
depends on NET_TCP
select MBEDTLS
select MBEDTLS_MD
select MBEDTLS_MAC_MD5_ENABLED
help
Implement Initial Sequence Number calculation as described in
RFC 6528 chapter 3. https://tools.ietf.org/html/rfc6528
If this is not set, then sys_rand32_get() is used for ISN value.
config NET_TCP_REJECT_CONN_WITH_RST
bool "Reject connection attempts on unbound TCP ports with RST"
default y
help
If enabled, TCP stack will reject connection attempts on unbound ports
with TCP RST packet.
config NET_TCP_IPV6_ND_REACHABILITY_HINT
bool "Provide a reachability hint for IPv6 Neighbor Discovery"
depends on NET_TCP
depends on NET_IPV6_ND
help
If enabled, TCP stack will inform the IPv6 Neighbor Discovery process
about the active link to a specific neighbor by signaling recent
"forward progress" event as described in RFC 4861.
endif # NET_TCP
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