.. SPDX-License-Identifier: GPL-2.0

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Netfilter Conntrack Sysfs variables
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/proc/sys/net/netfilter/nf_conntrack_* Variables:
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nf_conntrack_acct - BOOLEAN
	- 0 - disabled (default)
	- not 0 - enabled

	Enable connection tracking flow accounting. 64-bit byte and packet
	counters per flow are added.

nf_conntrack_buckets - INTEGER
	Size of hash table. If not specified as parameter during module
	loading, the default size is calculated by dividing total memory
	by 16384 to determine the number of buckets. The hash table will
	never have fewer than 1024 and never more than 262144 buckets.
	This sysctl is only writeable in the initial net namespace.

nf_conntrack_checksum - BOOLEAN
	- 0 - disabled
	- not 0 - enabled (default)

	Verify checksum of incoming packets. Packets with bad checksums are
	in INVALID state. If this is enabled, such packets will not be
	considered for connection tracking.

nf_conntrack_count - INTEGER (read-only)
	Number of currently allocated flow entries.

nf_conntrack_events - BOOLEAN
	- 0 - disabled
	- 1 - enabled
	- 2 - auto (default)

	If this option is enabled, the connection tracking code will
	provide userspace with connection tracking events via ctnetlink.
	The default allocates the extension if a userspace program is
	listening to ctnetlink events.

nf_conntrack_expect_max - INTEGER
	Maximum size of expectation table.  Default value is
	nf_conntrack_buckets / 256. Minimum is 1.

nf_conntrack_frag6_high_thresh - INTEGER
	default 262144

	Maximum memory used to reassemble IPv6 fragments.  When
	nf_conntrack_frag6_high_thresh bytes of memory is allocated for this
	purpose, the fragment handler will toss packets until
	nf_conntrack_frag6_low_thresh is reached.

nf_conntrack_frag6_low_thresh - INTEGER
	default 196608

	See nf_conntrack_frag6_low_thresh

nf_conntrack_frag6_timeout - INTEGER (seconds)
	default 60

	Time to keep an IPv6 fragment in memory.

nf_conntrack_generic_timeout - INTEGER (seconds)
	default 600

	Default for generic timeout.  This refers to layer 4 unknown/unsupported
	protocols.

nf_conntrack_helper - BOOLEAN
	- 0 - disabled (default)
	- not 0 - enabled

	Enable automatic conntrack helper assignment.
	If disabled it is required to set up iptables rules to assign
	helpers to connections.  See the CT target description in the
	iptables-extensions(8) man page for further information.

nf_conntrack_icmp_timeout - INTEGER (seconds)
	default 30

	Default for ICMP timeout.

nf_conntrack_icmpv6_timeout - INTEGER (seconds)
	default 30

	Default for ICMP6 timeout.

nf_conntrack_log_invalid - INTEGER
	- 0   - disable (default)
	- 1   - log ICMP packets
	- 6   - log TCP packets
	- 17  - log UDP packets
	- 33  - log DCCP packets
	- 41  - log ICMPv6 packets
	- 136 - log UDPLITE packets
	- 255 - log packets of any protocol

	Log invalid packets of a type specified by value.

nf_conntrack_max - INTEGER
        Maximum number of allowed connection tracking entries. This value is set
        to nf_conntrack_buckets by default.
        Note that connection tracking entries are added to the table twice -- once
        for the original direction and once for the reply direction (i.e., with
        the reversed address). This means that with default settings a maxed-out
        table will have a average hash chain length of 2, not 1.

nf_conntrack_tcp_be_liberal - BOOLEAN
	- 0 - disabled (default)
	- not 0 - enabled

	Be conservative in what you do, be liberal in what you accept from others.
	If it's non-zero, we mark only out of window RST segments as INVALID.

nf_conntrack_tcp_ignore_invalid_rst - BOOLEAN
	- 0 - disabled (default)
	- 1 - enabled

	If it's 1, we don't mark out of window RST segments as INVALID.

nf_conntrack_tcp_loose - BOOLEAN
	- 0 - disabled
	- not 0 - enabled (default)

	If it is set to zero, we disable picking up already established
	connections.

nf_conntrack_tcp_max_retrans - INTEGER
	default 3

	Maximum number of packets that can be retransmitted without
	received an (acceptable) ACK from the destination. If this number
	is reached, a shorter timer will be started.

nf_conntrack_tcp_timeout_close - INTEGER (seconds)
	default 10

nf_conntrack_tcp_timeout_close_wait - INTEGER (seconds)
	default 60

nf_conntrack_tcp_timeout_established - INTEGER (seconds)
	default 432000 (5 days)

nf_conntrack_tcp_timeout_fin_wait - INTEGER (seconds)
	default 120

nf_conntrack_tcp_timeout_last_ack - INTEGER (seconds)
	default 30

nf_conntrack_tcp_timeout_max_retrans - INTEGER (seconds)
	default 300

nf_conntrack_tcp_timeout_syn_recv - INTEGER (seconds)
	default 60

nf_conntrack_tcp_timeout_syn_sent - INTEGER (seconds)
	default 120

nf_conntrack_tcp_timeout_time_wait - INTEGER (seconds)
	default 120

nf_conntrack_tcp_timeout_unacknowledged - INTEGER (seconds)
	default 300

nf_conntrack_timestamp - BOOLEAN
	- 0 - disabled (default)
	- not 0 - enabled

	Enable connection tracking flow timestamping.

nf_conntrack_udp_timeout - INTEGER (seconds)
	default 30

nf_conntrack_udp_timeout_stream - INTEGER (seconds)
	default 120

	This extended timeout will be used in case there is an UDP stream
	detected.

nf_conntrack_gre_timeout - INTEGER (seconds)
	default 30

nf_conntrack_gre_timeout_stream - INTEGER (seconds)
	default 180

	This extended timeout will be used in case there is an GRE stream
	detected.

nf_hooks_lwtunnel - BOOLEAN
	- 0 - disabled (default)
	- not 0 - enabled

	If this option is enabled, the lightweight tunnel netfilter hooks are
	enabled. This option cannot be disabled once it is enabled.

nf_flowtable_tcp_timeout - INTEGER (seconds)
        default 30

        Control offload timeout for tcp connections.
        TCP connections may be offloaded from nf conntrack to nf flow table.
        Once aged, the connection is returned to nf conntrack with tcp pickup timeout.

nf_flowtable_udp_timeout - INTEGER (seconds)
        default 30

        Control offload timeout for udp connections.
        UDP connections may be offloaded from nf conntrack to nf flow table.
        Once aged, the connection is returned to nf conntrack with udp pickup timeout.