.. SPDX-License-Identifier: GPL-2.0

=====================
MPTCP Sysfs variables
=====================

/proc/sys/net/mptcp/* Variables
===============================

add_addr_timeout - INTEGER (seconds)
	Set the maximum value of timeout after which an ADD_ADDR control message
	will be resent to an MPTCP peer that has not acknowledged a previous
	ADD_ADDR message. A dynamically estimated retransmission timeout based
	on the estimated connection round-trip-time is used if this value is
	lower than the maximum one.

	Do not retransmit if set to 0.

	The default value matches TCP_RTO_MAX. This is a per-namespace
	sysctl.

	Default: 120

add_addr_v6_port_drop_ts - BOOLEAN
	Control whether preparing an ADD_ADDR with an IPv6 address and a port
	should drop the TCP timestamps option to have enough option space to
	send the signal.

	If there is not enough option space, and the TCP timestamps option
	cannot be dropped, the signal cannot be sent. Note that dropping the TCP
	timestamps option for one packet of the connection could disrupt some
	middleboxes: even if it should be unlikely, they could drop the packet
	or block the connection. This is a per-namespace sysctl.

	Default: 1 (enabled)

allow_join_initial_addr_port - BOOLEAN
	Allow peers to send join requests to the IP address and port number used
	by the initial subflow if the value is 1. This controls a flag that is
	sent to the peer at connection time, and whether such join requests are
	accepted or denied.

	Joins to addresses advertised with ADD_ADDR are not affected by this
	value.

	This is a per-namespace sysctl.

	Default: 1

available_path_managers - STRING
	Shows the available path managers choices that are registered. More
	path managers may be available, but not loaded.

available_schedulers - STRING
	Shows the available schedulers choices that are registered. More packet
	schedulers may be available, but not loaded.

blackhole_timeout - INTEGER (seconds)
	Initial time period in second to disable MPTCP on active MPTCP sockets
	when a MPTCP firewall blackhole issue happens. This time period will
	grow exponentially when more blackhole issues get detected right after
	MPTCP is re-enabled and will reset to the initial value when the
	blackhole issue goes away.

	0 to disable the blackhole detection. This is a per-namespace sysctl.

	Default: 3600

checksum_enabled - BOOLEAN
	Control whether DSS checksum can be enabled.

	DSS checksum can be enabled if the value is nonzero. This is a
	per-namespace sysctl.

	Default: 0

close_timeout - INTEGER (seconds)
	Set the make-after-break timeout: in absence of any close or
	shutdown syscall, MPTCP sockets will maintain the status
	unchanged for such time, after the last subflow removal, before
	moving to TCP_CLOSE.

	The default value matches TCP_TIMEWAIT_LEN. This is a per-namespace
	sysctl.

	Default: 60

enabled - BOOLEAN
	Control whether MPTCP sockets can be created.

	MPTCP sockets can be created if the value is 1. This is a
	per-namespace sysctl.

	Default: 1 (enabled)

path_manager - STRING
	Set the default path manager name to use for each new MPTCP
	socket. In-kernel path management will control subflow
	connections and address advertisements according to
	per-namespace values configured over the MPTCP netlink
	API. Userspace path management puts per-MPTCP-connection subflow
	connection decisions and address advertisements under control of
	a privileged userspace program, at the cost of more netlink
	traffic to propagate all of the related events and commands.

	This is a per-namespace sysctl.

	* "kernel"          - In-kernel path manager
	* "userspace"       - Userspace path manager

	Default: "kernel"

pm_type - INTEGER
	Set the default path manager type to use for each new MPTCP
	socket. In-kernel path management will control subflow
	connections and address advertisements according to
	per-namespace values configured over the MPTCP netlink
	API. Userspace path management puts per-MPTCP-connection subflow
	connection decisions and address advertisements under control of
	a privileged userspace program, at the cost of more netlink
	traffic to propagate all of the related events and commands.

	This is a per-namespace sysctl.

	Deprecated since v6.15, use path_manager instead.

	* 0 - In-kernel path manager
	* 1 - Userspace path manager

	Default: 0

scheduler - STRING
	Select the scheduler of your choice.

	Support for selection of different schedulers. This is a per-namespace
	sysctl.

	Default: "default"

stale_loss_cnt - INTEGER
	The number of MPTCP-level retransmission intervals with no traffic and
	pending outstanding data on a given subflow required to declare it stale.
	The packet scheduler ignores stale subflows.
	A low stale_loss_cnt  value allows for fast active-backup switch-over,
	an high value maximize links utilization on edge scenarios e.g. lossy
	link with high BER or peer pausing the data processing.

	This is a per-namespace sysctl.

	Default: 4

syn_retrans_before_tcp_fallback - INTEGER
	The number of SYN + MP_CAPABLE retransmissions before falling back to
	TCP, i.e. dropping the MPTCP options. In other words, if all the packets
	are dropped on the way, there will be:

	* The initial SYN with MPTCP support
	* This number of SYN retransmitted with MPTCP support
	* The next SYN retransmissions will be without MPTCP support

	0 means the first retransmission will be done without MPTCP options.
	>= 128 means that all SYN retransmissions will keep the MPTCP options. A
	lower number might increase false-positive MPTCP blackholes detections.
	This is a per-namespace sysctl.

	Default: 2
