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+.. SPDX-License-Identifier: GPL-2.0
+
+===================================
+Netfilter Conntrack Sysfs variables
+===================================
+
+/proc/sys/net/netfilter/nf_conntrack_* Variables:
+=================================================
+
+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_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.