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4. nf_conntrack-sysctl.txt

/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 (read-only)
	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 but the hash table will
	never have fewer than 32 or more than 16384 buckets.

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
	not 0 - enabled (default)

	If this option is enabled, the connection tracking code will
	provide userspace with connection tracking events via ctnetlink.

nf_conntrack_events_retry_timeout - INTEGER (seconds)
	default 15

	This option is only relevant when "reliable connection tracking
	events" are used.  Normally, ctnetlink is "lossy", that is,
	events are normally dropped when userspace listeners can't keep up.

	Userspace can request "reliable event mode".  When this mode is
	active, the conntrack will only be destroyed after the event was
	delivered.  If event delivery fails, the kernel periodically
	re-tries to send the event to userspace.

	This is the maximum interval the kernel should use when re-trying
	to deliver the destroy event.

	A higher number means there will be fewer delivery retries and it
	will take longer for a backlog to be processed.

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
	not 0 - enabled (default)

	Enable automatic conntrack helper assignment.

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
	Size of connection tracking table.  Default value is
	nf_conntrack_buckets value * 4.

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_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_stream2 - INTEGER (seconds)
	default 180

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