/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 packetcounters per flow are added.

nf_conntrack_buckets - INTEGER

Size of hash table. If not specified as parameter during moduleloading, the default size is calculated by dividing total memoryby 16384 to determine the number of buckets. The hash table willnever 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 arein INVALID state. If this is enabled, such packets will not beconsidered 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 willprovide userspace with connection tracking events via ctnetlink.The default allocates the extension if a userspace program islistening to ctnetlink events.

nf_conntrack_expect_max - INTEGER

Maximum size of expectation table. Default value isnf_conntrack_buckets / 256. Minimum is 1.

nf_conntrack_frag6_high_thresh - INTEGER

default 262144

Maximum memory used to reassemble IPv6 fragments. Whennf_conntrack_frag6_high_thresh bytes of memory is allocated for thispurpose, the fragment handler will toss packets untilnf_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/unsupportedprotocols.

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

• 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 setto nf_conntrack_buckets by default.Note that connection tracking entries are added to the table twice -- oncefor the original direction and once for the reply direction (i.e., withthe reversed address). This means that with default settings a maxed-outtable 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 establishedconnections.

nf_conntrack_tcp_max_retrans - INTEGER

default 3

Maximum number of packets that can be retransmitted withoutreceived an (acceptable) ACK from the destination. If this numberis 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_sctp_timeout_closed - INTEGER (seconds)

default 10

nf_conntrack_sctp_timeout_cookie_wait - INTEGER (seconds)

default 3

nf_conntrack_sctp_timeout_cookie_echoed - INTEGER (seconds)

default 3

nf_conntrack_sctp_timeout_established - INTEGER (seconds)

default 210

Default is set to (hb_interval * path_max_retrans + rto_max)

nf_conntrack_sctp_timeout_shutdown_sent - INTEGER (seconds)

default 3

nf_conntrack_sctp_timeout_shutdown_recd - INTEGER (seconds)

default 3

nf_conntrack_sctp_timeout_shutdown_ack_sent - INTEGER (seconds)

default 3

nf_conntrack_sctp_timeout_heartbeat_sent - INTEGER (seconds)

default 30

This timeout is used to setup conntrack entry on secondary paths.Default is set to hb_interval.

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 streamdetected.

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 streamdetected.

nf_hooks_lwtunnel - BOOLEAN

• 0 - disabled (default)

• not 0 - enabled

If this option is enabled, the lightweight tunnel netfilter hooks areenabled. 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.

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.