1# TCP options
2
3# Copyright (c) 2016 Intel Corporation.
4# Copyright (c) 2021 Nordic Semiconductor
5# Copyright (c) 2023 Arm Limited (or its affiliates). All rights reserved.
6# SPDX-License-Identifier: Apache-2.0
7
8menuconfig NET_TCP
9	bool "TCP"
10	depends on NET_IP
11	help
12	  The value depends on your network needs.
13
14if NET_TCP
15
16if NET_TCP
17module = NET_TCP
18module-dep = NET_LOG
19module-str = Log level for TCP
20module-help = Enables TCP handler output debug messages
21source "subsys/net/Kconfig.template.log_config.net"
22endif # NET_TCP
23
24config NET_TCP_WORKQ_STACK_SIZE
25	int "TCP work queue thread stack size"
26	default 1200 if X86
27	default 1024
28	depends on NET_TCP
29	help
30	  Set the TCP work queue thread stack size in bytes.
31
32config NET_TCP_WORKER_PRIO
33	int "Priority of the TCP work queue"
34	default 2
35	depends on NET_TCP
36	help
37	  Set the priority of the TCP worker queue, that handles all
38	  transmission and maintenance within the TCP stack.
39	  Value 0 = highest priortity.
40	  When CONFIG_NET_TC_THREAD_COOPERATIVE = y, lowest priority is
41	  CONFIG_NUM_COOP_PRIORITIES-1 else lowest priority is
42	  CONFIG_NUM_PREEMPT_PRIORITIES-1.
43	  Make sure the priority is lower than lower layer TX threads to
44	  avoid the TCP stack consume all net_bufs before transferring
45	  execution to the lower layer network stack, with a high risk of
46	  running out of net_bufs.
47
48config NET_TCP_TIME_WAIT_DELAY
49	int "How long to wait in TIME_WAIT state (in milliseconds)"
50	depends on NET_TCP
51	default 1500
52	help
53	  To avoid a (low-probability) issue when delayed packets from
54	  previous connection get delivered to next connection reusing
55	  the same local/remote ports, RFC 793 (TCP) suggests to keep
56	  an old, closed connection in a special "TIME_WAIT" state for
57	  the duration of 2*MSL (Maximum Segment Lifetime). The RFC
58	  suggests to use MSL of 2 minutes, but notes "This is an
59	  engineering choice, and may be changed if experience indicates
60	  it is desirable to do so." For low-resource systems, having
61	  large MSL may lead to quick resource exhaustion (and related
62	  DoS attacks). At the same time, the issue of packet misdelivery
63	  is largely alleviated in the modern TCP stacks by using random,
64	  non-repeating port numbers and initial sequence numbers. Due
65	  to this, Zephyr uses much lower value of 1500ms by default.
66	  Value of 0 disables TIME_WAIT state completely.
67
68config NET_TCP_ACK_TIMEOUT
69	int "How long to wait for ACK (in milliseconds)"
70	depends on NET_TCP
71	default 1000
72	range 1 2147483647
73	help
74	  This value affects the timeout when waiting ACK to arrive in
75	  various TCP states. The value is in milliseconds. Note that
76	  having a very low value here could prevent connectivity.
77
78config NET_TCP_INIT_RETRANSMISSION_TIMEOUT
79	int "Initial value of Retransmission Timeout (RTO) (in milliseconds)"
80	depends on NET_TCP
81	default 200
82	range 100 60000
83	help
84	  This value affects the timeout between initial retransmission
85	  of TCP data packets. The value is in milliseconds.
86
87config NET_TCP_RANDOMIZED_RTO
88	bool "Use a randomized retransmission time"
89	default y
90	depends on NET_TCP
91	help
92	  It can happen that two similar stacks enter a retransmission cycle
93	  due to a packet collision. If the transmission timeout is the same
94	  both stacks will retry at the same moment resulting in another
95	  collision. By introducing a randomized retry timeout, the chance of
96	  a second collision is reduced and it reduces furter the more
97	  retransmissions occur.
98
99config NET_TCP_RETRY_COUNT
100	int "Maximum number of TCP segment retransmissions"
101	depends on NET_TCP
102	default 9
103	help
104	  The following formula can be used to determine the time (in ms)
105	  that a segment will be be buffered awaiting retransmission:
106	  n=NET_TCP_RETRY_COUNT
107	  Sum((1<<n) * NET_TCP_INIT_RETRANSMISSION_TIMEOUT)
108	  n=0
109	  With the default value of 9, the IP stack will try to
110	  retransmit for up to 1:42 minutes.  This is as close as possible
111	  to the minimum value recommended by RFC1122 (1:40 minutes).
112	  Only 5 bits are dedicated for the retransmission count, so accepted
113	  values are in the 0-31 range.  It's highly recommended to not go
114	  below 9, though.
115	  Should a retransmission timeout occur, the receive callback is
116	  called with -ETIMEDOUT error code and the context is dereferenced.
117
118config NET_TCP_MAX_SEND_WINDOW_SIZE
119	int "Maximum sending window size to use"
120	depends on NET_TCP
121	default 0
122	range 0 65535
123	help
124	  This value affects how the TCP selects the maximum sending window
125	  size. The default value 0 lets the TCP stack select the value
126	  according to amount of network buffers configured in the system.
127
128config NET_TCP_MAX_RECV_WINDOW_SIZE
129	int "Maximum receive window size to use"
130	depends on NET_TCP
131	default 0
132	range 0 65535
133	help
134	  This value defines the maximum TCP receive window size. Increasing
135	  this value can improve connection throughput, but requires more
136	  receive buffers available in the system for efficient operation.
137	  The default value 0 lets the TCP stack select the value
138	  according to amount of network buffers configured in the system.
139
140config NET_TCP_RECV_QUEUE_TIMEOUT
141	int "How long to queue received data (in ms)"
142	depends on NET_TCP
143	default 2000
144	range 0 10000
145	help
146	  If we receive out-of-order TCP data, we queue it. This value tells
147	  how long the data is kept before it is discarded if we have not been
148	  able to pass the data to the application. If set to 0, then receive
149	  queueing is not enabled. The value is in milliseconds.
150	  Note that we only queue data sequentially in current version i.e.,
151	  there should be no holes in the queue. For example, if we receive
152	  SEQs 5,4,3,6 and are waiting SEQ 2, the data in segments 3,4,5,6 is
153	  queued (in this order), and then given to application when we receive
154	  SEQ 2. But if we receive SEQs 5,4,3,7 then the SEQ 7 is discarded
155	  because the list would not be sequential as number 6 is be missing.
156
157config NET_TCP_PKT_ALLOC_TIMEOUT
158	int "How long to wait for a TCP packet allocation (in ms)"
159	depends on NET_TCP
160	default 100
161	range 10 1000
162	help
163	  The TCP network stack allocates packets from the buffers and the
164	  allocation can take some time depending on the situation.
165	  This value indicates how long the stack should wait for the packet to
166	  be allocated, before returning an internal error and trying again.
167
168config NET_TCP_CHECKSUM
169	bool "Check TCP checksum"
170	default y
171	depends on NET_TCP
172	help
173	  Enables TCP handler to check TCP checksum. If the checksum is invalid,
174	  then the packet is discarded.
175
176config NET_TCP_FAST_RETRANSMIT
177	bool "Fast-retry algorithm based on the number of duplicated ACKs"
178	depends on NET_TCP
179	default y
180	help
181	  When a packet is lost, the receiver will keep acknowledging the
182	  sequence number of the last correctly received byte. Upon reception
183	  of a sequence of acknowledgements for the same sequence number,
184	  this can be deduced as that the packet afterwards must have been lost.
185	  In that case a retransmission is triggered to avoid having to wait for
186	  the retransmit timer to elapse.
187
188config NET_TCP_CONGESTION_AVOIDANCE
189	bool "Implement a congestion avoidance algorithm in TCP"
190	depends on NET_TCP
191	default y
192	help
193	  To avoid overstressing a link reduce the transmission rate as soon as
194	  packets are starting to drop.
195
196config NET_TCP_KEEPALIVE
197	bool "TCP keep-alive support"
198	depends on NET_TCP
199	help
200	  Enabling this option allows the TCP stack to send periodic TCP
201	  keep-alive probes. Enables SO_KEEPALIVE, TCP_KEEPIDLE, TCP_KEEPINTVL
202	  and TCP_KEEPCNT options processing.
203
204config NET_TCP_KEEPIDLE_DEFAULT
205	int "TCP_KEEPIDLE default value"
206	depends on NET_TCP_KEEPALIVE
207	default 7200
208	help
209	  The time (in seconds) the connection needs to remain idle before TCP
210	  starts sending keepalive probes, if the socket option SO_KEEPALIVE has
211	  been set on this socket.
212
213config NET_TCP_KEEPINTVL_DEFAULT
214	int "TCP_KEEPINTVL default value"
215	depends on NET_TCP_KEEPALIVE
216	default 75
217	help
218	  The time (in seconds) between individual keepalive probes.
219
220config NET_TCP_KEEPCNT_DEFAULT
221	int "TCP_KEEPCNT default value"
222	depends on NET_TCP_KEEPALIVE
223	default 9
224	help
225	  The maximum number of keepalive probes TCP should send before dropping
226	  the connection.
227
228config NET_TCP_ISN_RFC6528
229	bool "Use ISN algorithm from RFC 6528"
230	default y
231	depends on NET_TCP
232	select MBEDTLS
233	select MBEDTLS_MD
234	select MBEDTLS_MAC_MD5_ENABLED
235	help
236	  Implement Initial Sequence Number calculation as described in
237	  RFC 6528 chapter 3. https://tools.ietf.org/html/rfc6528
238	  If this is not set, then sys_rand32_get() is used for ISN value.
239
240config NET_TCP_REJECT_CONN_WITH_RST
241	bool "Reject connection attempts on unbound TCP ports with RST"
242	default y
243	help
244	  If enabled, TCP stack will reject connection attempts on unbound ports
245	  with TCP RST packet.
246
247config NET_TCP_IPV6_ND_REACHABILITY_HINT
248	bool "Provide a reachability hint for IPv6 Neighbor Discovery"
249	depends on NET_TCP
250	depends on NET_IPV6_ND
251	help
252	  If enabled, TCP stack will inform the IPv6 Neighbor Discovery process
253	  about the active link to a specific neighbor by signaling recent
254	  "forward progress" event as described in RFC 4861.
255
256endif # NET_TCP
257