/proc/sys/net/ipv4/* Variables:
吴飞语
/proc/sys/net/ipv4/* Variables:
ip_forward - BOOLEAN 0 - disabled (default)
not 0 - enabled
Forward Packets between interfaces.
This variable is special, its change resets all configuration parameters to their default state (RFC1122 for hosts, RFC1812
for routers)
ip_default_ttl - INTEGER default 64
ip_no_pmtu_disc - BOOLEAN Disable Path MTU Discovery.
default FALSE
min_pmtu - INTEGER default 562 - minimum discovered Path MTU
mtu_expires - INTEGER Time, in seconds, that cached PMTU information is kept.
min_adv_mss - INTEGER The advertised MSS depends on the first hop route MTU, but will
never be lower than this setting.
rt_cache_rebuild_count - INTEGER The per net-namespace route cache emergency rebuild threshold.
Any net-namespace having its route cache rebuilt due to
a hash bucket chain being too long more than this many times
will have its route caching disabled
IP Fragmentation:
ipfrag_high_thresh - INTEGER Maximum memory used to reassemble IP fragments. When
ipfrag_high_thresh bytes of memory is allocated for this purpose,
the fragment handler will toss packets until ipfrag_low_thresh
is reached.
ipfrag_low_thresh - INTEGER See ipfrag_high_thresh
ipfrag_time - INTEGER Time in seconds to keep an IP fragment in memory.
ipfrag_secret_interval - INTEGER Regeneration interval (in seconds) of the hash secret (or lifetime
for the hash secret) for IP fragments.
Default: 600
ipfrag_max_dist - INTEGER ipfrag_max_dist is a non-negative integer value which defines the maximum "disorder" which is allowed among fragments which share a
common IP source address. Note that reordering of packets is
not unusual, but if a large number of fragments arrive from a source
IP address while a particular fragment queue remains incomplete, it probably indicates that one or more fragments belonging to that queue have been lost. When ipfrag_max_dist is positive, an additional check
is done on fragments before they are added to a reassembly queue - if ipfrag_max_dist (or more) fragments have arrived from a particular IP address between additions to any IP fragment queue using that source address, it's presumed that one or more fragments in the queue are
lost. The existing fragment queue will be dropped, and a new one started. An ipfrag_max_dist value of zero disables this check.
Using a very small value, e.g. 1 or 2, for ipfrag_max_dist can
result in unnecessarily dropping fragment queues when normal
reordering of packets occurs, which could lead to poor application performance. Using a very large value, e.g. 50000, increases the likelihood of incorrectly reassembling IP fragments that originate
from different IP datagrams, which could result in data corruption. Default: 64
INET peer storage:
inet_peer_threshold - INTEGER The approximate size of the storage. Starting from this threshold entries will be thrown aggressively. This threshold also determines entries' time-to-live and time intervals between garbage collection passes. More entries, less time-to-live, less GC interval.
inet_peer_minttl - INTEGER Minimum time-to-live of entries. Should be enough to cover fragment time-to-live on the reassembling side. This minimum time-to-live is guaranteed if the pool size is less than inet_peer_threshold.
Measured in seconds.
inet_peer_maxttl - INTEGER Maximum time-to-live of entries. Unused entries will expire after
this period of time if there is no memory pressure on the pool (i.e. when the number of entries in the pool is very small).
Measured in seconds.
inet_peer_gc_mintime - INTEGER Minimum interval between garbage collection passes. This interval is
in effect under high memory pressure on the pool.
Measured in seconds.
inet_peer_gc_maxtime - INTEGER Minimum interval between garbage collection passes. This interval is
in effect under low (or absent) memory pressure on the pool.
Measured in seconds.
TCP variables:
somaxconn - INTEGER Limit of socket listen() backlog, known in userspace as SOMAXCONN. Defaults to 128. See also tcp_max_syn_backlog for additional tuning
for TCP sockets.
tcp_abc - INTEGER Controls Appropriate Byte Count (ABC) defined in RFC3465.
ABC is a way of increasing congestion window (cwnd) more slowly
in response to partial acknowledgments.
Possible values are: 0 increase cwnd once per acknowledgment (no ABC) 1 increase cwnd once per acknowledgment of full sized segment 2 allow increase cwnd by two if acknowledgment is of two segments to compensate for delayed acknowledgments. Default: 0 (off)
tcp_abort_on_overflow - BOOLEAN If listening service is too slow to accept new connections,
reset them. Default state is FALSE. It means that if overflow
occurred due to a burst, connection will recover. Enable this
option _only_ if you are really sure that listening daemon
cannot be tuned to accept connections faster. Enabling this
option can harm clients of your server.
tcp_adv_win_scale - INTEGER Count buffering overhead as bytes/2^tcp_adv_win_scale
(if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale),
if it is <= 0.
Default: 2
tcp_allowed_congestion_control - STRING Show/set the congestion control choices available to non-privileged processes. The list is a subset of those listed in tcp_available_congestion_control.
Default is "reno" and the default setting (tcp_congestion_control).
tcp_app_win - INTEGER Reserve max(window/2^tcp_app_win, mss) of window for application
buffer. Value 0 is special, it means that nothing is reserved.
Default: 31
tcp_available_congestion_control - STRING Shows the available congestion control choices that are registered.
More congestion control algorithms may be available as modules,
but not loaded.
tcp_base_mss - INTEGER The initial value of search_low to be used by the packetization layer Path MTU discovery (MTU probing). If MTU probing is enabled,
this is the initial MSS used by the connection.
tcp_congestion_control - STRING Set the congestion control algorithm to be used for new
connections. The algorithm "reno" is always available, but
additional choices may be available based on kernel configuration. Default is set as part of kernel configuration.
tcp_dsack - BOOLEAN Allows TCP to send "duplicate" SACKs.
tcp_ecn - BOOLEAN Enable Explicit Congestion Notification (ECN) in TCP. ECN is only
used when both ends of the TCP flow support it. It is useful to
avoid losses due to congestion (when the bottleneck router supports
ECN).
Possible values are: 0 disable ECN 1 ECN enabled 2 Only server-side ECN enabled. If the other end does not support ECN, behavior is like with ECN disabled. Default: 2
tcp_fack - BOOLEAN Enable FACK congestion avoidance and fast retransmission.
The value is not used, if tcp_sack is not enabled.
tcp_fin_timeout - INTEGER Time to hold socket in state FIN-WAIT-2, if it was closed
by our side. Peer can be broken and never close its side,
or even died unexpectedly. Default value is 60sec.
Usual value used in 2.2 was 180 seconds, you may restore
it, but remember that if your machine is even underloaded WEB server, you risk to overflow memory with kilotons of dead sockets,
FIN-WAIT-2 sockets are less dangerous than FIN-WAIT-1,
because they eat maximum 1.5K of memory, but they tend
to live longer. Cf. tcp_max_orphans.
tcp_frto - INTEGER Enables Forward RTO-Recovery (F-RTO) defined in RFC4138.
F-RTO is an enhanced recovery algorithm for TCP retransmission
timeouts. It is particularly beneficial in wireless environments
where packet loss is typically due to random radio interference
rather than intermediate router congestion. F-RTO is sender-side
only modification. Therefore it does not require any support from
the peer.
If set to 1, basic version is enabled. 2 enables SACK enhanced
F-RTO if flow uses SACK. The basic version can be used also when
SACK is in use though scenario(s) with it exists where F-RTO
interacts badly with the packet counting of the SACK enabled TCP
flow.
tcp_frto_response - INTEGER When F-RTO has detected that a TCP retransmission timeout was
spurious (i.e, the timeout would have been avoided had TCP set a
longer retransmission timeout), TCP has several options what to do
next. Possible values are: 0 Rate halving based; a smooth and conservative response, results in halved cwnd and ssthresh after one RTT 1 Very conservative response; not recommended because even though being valid, it interacts poorly with the rest of
Linux TCP, halves cwnd and ssthresh immediately 2 Aggressive response; undoes congestion control measures that are now known to be unnecessary (ignoring the
possibility of a lost retransmission that would require
TCP to be more cautious), cwnd and ssthresh are restored
to the values prior timeout Default: 0 (rate halving based)
tcp_keepalive_time - INTEGER How often TCP sends out keepalive messages when keepalive is enabled. Default: 2hours.
tcp_keepalive_probes - INTEGER How many keepalive probes TCP sends out, until it decides that the connection is broken. Default value: 9.
tcp_keepalive_intvl - INTEGER How frequently the probes are send out. Multiplied by tcp_keepalive_probes it is time to kill not responding connection,
after probes started. Default value: 75sec i.e. connection
will be aborted after ~11 minutes of retries.
tcp_low_latency - BOOLEAN If set, the TCP stack makes decisions that prefer lower
latency as opposed to higher throughput. By default, this
option is not set meaning that higher throughput is preferred.
An example of an application where this default should be
changed would be a Beowulf compute cluster.
Default: 0
tcp_max_orphans - INTEGER Maximal number of TCP sockets not attached to any user file handle,
held by system. If this number is exceeded orphaned connections are reset immediately and warning is printed. This limit exists
only to prevent simple DoS attacks, you _must_ not rely on this
or lower the limit artificially, but rather increase it
(probably, after increasing installed memory),
if network conditions require more than default value,
and tune network services to linger and kill such states
more aggressively. Let me to remind again: each orphan eats
up to ~64K of unswappable memory.
tcp_max_syn_backlog - INTEGER Maximal number of remembered connection requests, which are
still did not receive an acknowledgment from connecting client.
Default value is 1024 for systems with more than 128Mb of memory,
and 128 for low memory machines. If server suffers of overload,
try to increase this number.
tcp_max_tw_buckets - INTEGER Maximal number of timewait sockets held by system simultaneously.
If this number is exceeded time-wait socket is immediately destroyed and warning is printed. This limit exists only to prevent
simple DoS attacks, you _must_ not lower the limit artificially,
but rather increase it (probably, after increasing installed memory), if network conditions require more than default value.
tcp_mem - vector of 3 INTEGERs: min, pressure, max min: below this number of pages TCP is not bothered about its
memory appetite.
pressure: when amount of memory allocated by TCP exceeds this number
of pages, TCP moderates its memory consumption and enters memory pressure mode, which is exited when memory consumption falls
under "min".
max: number of pages allowed for queueing by all TCP sockets.
Defaults are calculated at boot time from amount of available
memory.
tcp_moderate_rcvbuf - BOOLEAN If set, TCP performs receive buffer auto-tuning, attempting to automatically size the buffer (no greater than tcp_rmem[2]) to
match the size required by the path for full throughput. Enabled by default.
tcp_mtu_probing - INTEGER Controls TCP Packetization-Layer Path MTU Discovery. Takes three
values: 0 - Disabled 1 - Disabled by default, enabled when an ICMP black hole detected 2 - Always enabled, use initial MSS of tcp_base_mss.
tcp_no_metrics_save - BOOLEAN By default, TCP saves various connection metrics in the route cache
when the connection closes, so that connections established in the
near future can use these to set initial conditions. Usually, this increases overall performance, but may sometimes cause performance degradation. If set, TCP will not cache metrics on closing
connections.
tcp_orphan_retries - INTEGER This value influences the timeout of a locally closed TCP connection, when RTO retransmissions remain unacknowledged.
See tcp_retries2 for more details.
The default value is 7.
If your machine is a loaded WEB server,
you should think about lowering this value, such sockets
may consume significant resources. Cf. tcp_max_orphans.
tcp_reordering - INTEGER Maximal reordering of packets in a TCP stream.
Default: 3
tcp_retrans_collapse - BOOLEAN Bug-to-bug compatibility with some broken printers.
On retransmit try to send bigger packets to work around bugs in
certain TCP stacks.
tcp_retries1 - INTEGER This value influences the time, after which TCP decides, that
something is wrong due to unacknowledged RTO retransmissions,
and reports this suspicion to the network layer.
See tcp_retries2 for more details.
RFC 1122 recommends at least 3 retransmissions, which is the
default.
tcp_retries2 - INTEGER This value influences the timeout of an alive TCP connection,
when RTO retransmissions remain unacknowledged.
Given a value of N, a hypothetical TCP connection following
exponential backoff with an initial RTO of TCP_RTO_MIN would
retransmit N times before killing the connection at the (N+1)th RTO.
The default value of 15 yields a hypothetical timeout of 924.6
seconds and is a lower bound for the effective timeout.
TCP will effectively time out at the first RTO which exceeds the hypothetical timeout.
RFC 1122 recommends at least 100 seconds for the timeout,
which corresponds to a value of at least 8.
tcp_rfc1337 - BOOLEAN If set, the TCP stack behaves conforming to RFC1337. If unset,
we are not conforming to RFC, but prevent TCP TIME_WAIT
assassination.
Default: 0
tcp_rmem - vector of 3 INTEGERs: min, default, max min: Minimal size of receive buffer used by TCP sockets.
It is guaranteed to each TCP socket, even under moderate memory pressure.
Default: 8K
default: initial size of receive buffer used by TCP sockets.
This value overrides net.core.rmem_default used by other protocols. Default: 87380 bytes. This value results in window of 65535 with
default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit
less for default tcp_app_win. See below about these variables.
max: maximal size of receive buffer allowed for automatically
selected receiver buffers for TCP socket. This value does not override net.core.rmem_max. Calling setsockopt() with SO_RCVBUF disables automatic tuning of that socket's receive buffer size, in which
case this value is ignored.
Default: between 87380B and 4MB, depending on RAM size.
tcp_sack - BOOLEAN Enable select acknowledgments (SACKS).
tcp_slow_start_after_idle - BOOLEAN If set, provide RFC2861 behavior and time out the congestion
window after an idle period. An idle period is defined at
the current RTO. If unset, the congestion window will not
be timed out after an idle period.
Default: 1
tcp_stdurg - BOOLEAN Use the Host requirements interpretation of the TCP urgent pointer field. Most hosts use the older BSD interpretation, so if you turn this on Linux might not communicate correctly with them.
Default: FALSE
tcp_synack_retries - INTEGER Number of times SYNACKs for a passive TCP connection attempt will
be retransmitted. Should not be higher than 255. Default value
is 5, which corresponds to ~180seconds.
tcp_syncookies - BOOLEAN Only valid when the kernel was compiled with CONFIG_SYNCOOKIES
Send out syncookies when the syn backlog queue of a socket
overflows. This is to prevent against the common 'SYN flood attack' Default: FALSE
Note, that syncookies is fallback facility.
It MUST NOT be used to help highly loaded servers to stand
against legal connection rate. If you see SYN flood warnings
in your logs, but investigation shows that they occur
because of overload with legal connections, you should tune
another parameters until this warning disappear.
See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow.
syncookies seriously violate TCP protocol, do not allow
to use TCP extensions, can result in serious degradation
of some services (f.e. SMTP relaying), visible not by you,
but your clients and relays, contacting you. While you see
SYN flood warnings in logs not being really flooded, your server
is seriously misconfigured.
tcp_syn_retries - INTEGER Number of times initial SYNs for an active TCP connection attempt
will be retransmitted. Should not be higher than 255. Default value
is 5, which corresponds to ~180seconds.
tcp_timestamps - BOOLEAN Enable timestamps as defined in RFC1323.
tcp_tso_win_divisor - INTEGER This allows control over what percentage of the congestion window
can be consumed by a single TSO frame.
The setting of this parameter is a choice between burstiness and building larger TSO frames.
Default: 3
tcp_tw_recycle - BOOLEAN Enable fast recycling TIME-WAIT sockets. Default value is 0.
It should not be changed without advice/request of technical
experts.
tcp_tw_reuse - BOOLEAN Allow to reuse TIME-WAIT sockets for new connections when it is
safe from protocol viewpoint. Default value is 0.
It should not be changed without advice/request of technical
experts.
tcp_window_scaling - BOOLEAN Enable window scaling as defined in RFC1323.
tcp_wmem - vector of 3 INTEGERs: min, default, max min: Amount of memory reserved for send buffers for TCP sockets.
Each TCP socket has rights to use it due to fact of its birth.
Default: 4K
default: initial size of send buffer used by TCP sockets. This
value overrides net.core.wmem_default used by other protocols.
It is usually lower than net.core.wmem_default.
Default: 16K
max: Maximal amount of memory allowed for automatically tuned
send buffers for TCP sockets. This value does not override
net.core.wmem_max. Calling setsockopt() with SO_SNDBUF disables automatic tuning of that socket's send buffer size, in which case
this value is ignored.
Default: between 64K and 4MB, depending on RAM size.
tcp_workaround_signed_windows - BOOLEAN If set, assume no receipt of a window scaling option means the
remote TCP is broken and treats the window as a signed quantity.
If unset, assume the remote TCP is not broken even if we do
not receive a window scaling option from them.
Default: 0
tcp_dma_copybreak - INTEGER Lower limit, in bytes, of the size of socket reads that will be offloaded to a DMA copy engine, if one is present in the system
and CONFIG_NET_DMA is enabled.
Default: 4096
UDP variables:
udp_mem - vector of 3 INTEGERs: min, pressure, max Number of pages allowed for queueing by all UDP sockets.
min: Below this number of pages UDP is not bothered about its
memory appetite. When amount of memory allocated by UDP exceeds
this number, UDP starts to moderate memory usage.
pressure: This value was introduced to follow format of tcp_mem.
max: Number of pages allowed for queueing by all UDP sockets.
Default is calculated at boot time from amount of available memory.
udp_rmem_min - INTEGER Minimal size of receive buffer used by UDP sockets in moderation.
Each UDP socket is able to use the size for receiving data, even if total pages of UDP sockets exceed udp_mem pressure. The unit is byte. Default: 4096
udp_wmem_min - INTEGER Minimal size of send buffer used by UDP sockets in moderation.
Each UDP socket is able to use the size for sending data, even if
total pages of UDP sockets exceed udp_mem pressure. The unit is byte. Default: 4096
CIPSOv4 Variables:
cipso_cache_enable - BOOLEAN If set, enable additions to and lookups from the CIPSO label mapping cache. If unset, additions are ignored and lookups always result in a miss. However, regardless of the setting the cache is still
invalidated when required when means you can safely toggle this on and off and the cache will always be "safe".
Default: 1
cipso_cache_bucket_size - INTEGER The CIPSO label cache consists of a fixed size hash table with each
hash bucket containing a number of cache entries. This variable limits the number of entries in each hash bucket; the larger the value the
more CIPSO label mappings that can be cached. When the number of entries in a given hash bucket reaches this limit adding new entries causes the oldest entry in the bucket to be removed to make room. Default: 10
cipso_rbm_optfmt - BOOLEAN Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of
the CIPSO draft specification (see Documentation/netlabel for details). This means that when set the CIPSO tag will be padded with empty categories in order to make the packet data 32-bit aligned.
Default: 0
cipso_rbm_structvalid - BOOLEAN If set, do a very strict check of the CIPSO option when ip_options_compile() is called. If unset, relax the checks done during ip_options_compile(). Either way is "safe" as errors are caught else where in the CIPSO processing code but setting this to 0 (False) should result in less work (i.e. it should be faster) but could cause problems with other implementations that require strict checking.
Default: 0
IP Variables:
ip_local_port_range - 2 INTEGERS Defines the local port range that is used by TCP and UDP to
choose the local port. The first number is the first, the
second the last local port number. Default value depends on
amount of memory available on the system:
> 128Mb 32768-61000
< 128Mb 1024-4999 or even less.
This number defines number of active connections, which this
system can issue simultaneously to systems not supporting
TCP extensions (timestamps). With tcp_tw_recycle enabled
(i.e. by default) range 1024-4999 is enough to issue up to 2000 connections per second to systems supporting timestamps.
ip_nonlocal_bind - BOOLEAN If set, allows processes to bind() to non-local IP addresses,
which can be quite useful - but may break some applications.
Default: 0
ip_dynaddr - BOOLEAN If set non-zero, enables support for dynamic addresses.
If set to a non-zero value larger than 1, a kernel log
message will be printed when dynamic address rewriting
occurs.
Default: 0
icmp_echo_ignore_all - BOOLEAN If set non-zero, then the kernel will ignore all ICMP ECHO
requests sent to it.
Default: 0
icmp_echo_ignore_broadcasts - BOOLEAN If set non-zero, then the kernel will ignore all ICMP ECHO and
TIMESTAMP requests sent to it via broadcast/multicast.
Default: 1
icmp_ratelimit - INTEGER Limit the maximal rates for sending ICMP packets whose type matches icmp_ratemask (see below) to specific targets. 0 to disable any limiting,
otherwise the minimal space between responses in milliseconds.
Default: 1000
icmp_ratemask - INTEGER Mask made of ICMP types for which rates are being limited.
Significant bits: IHGFEDCBA9876543210
Default mask: 0000001100000011000 (6168)
Bit definitions (see include/linux/icmp.h): 0 Echo Reply 3 Destination Unreachable * 4 Source Quench * 5 Redirect 8 Echo Request
B Time Exceeded *
C Parameter Problem *
D Timestamp Request
E Timestamp Reply
F Info Request
G Info Reply
H Address Mask Request
I Address Mask Reply
* These are rate limited by default (see default mask above)
icmp_ignore_bogus_error_responses - BOOLEAN Some routers violate RFC1122 by sending bogus responses to broadcast frames. Such violations are normally logged via a kernel warning.
If this is set to TRUE, the kernel will not give such warnings, which will avoid log file clutter.
Default: FALSE
icmp_errors_use_inbound_ifaddr - BOOLEAN
If zero, icmp error messages are sent with the primary address of
the exiting interface.
If non-zero, the message will be sent with the primary address of
the interface that received the packet that caused the icmp error.
This is the behaviour network many administrators will expect from
a router. And it can make debugging complicated network layouts
much easier.
Note that if no primary address exists for the interface selected,
then the primary address of the first non-loopback interface that
has one will be used regardless of this setting.
Default: 0
igmp_max_memberships - INTEGER Change the maximum number of multicast groups we can subscribe to. Default: 20
conf/interface/* changes special settings per interface (where "interface" is the name of your network interface) conf/all/* is special, changes the settings for all interfaces
log_martians - BOOLEAN Log packets with impossible addresses to kernel log.
log_martians for the interface will be enabled if at least one of
conf/{all,interface}/log_martians is set to TRUE,
it will be disabled otherwise
accept_redirects - BOOLEAN Accept ICMP redirect messages.
accept_redirects for the interface will be enabled if:
- both conf/{all,interface}/accept_redirects are TRUE in the case forwarding for the interface is enabled or
- at least one of conf/{all,interface}/accept_redirects is TRUE in the case forwarding for the interface is disabled accept_redirects for the interface will be disabled otherwise
default TRUE (host) FALSE (router)
forwarding - BOOLEAN Enable IP forwarding on this interface.
mc_forwarding - BOOLEAN Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE and a multicast routing daemon is required.
conf/all/mc_forwarding must also be set to TRUE to enable multicast routing for the interface
medium_id - INTEGER Integer value used to differentiate the devices by the medium they
are attached to. Two devices can have different id values when
the broadcast packets are received only on one of them.
The default value 0 means that the device is the only interface
to its medium, value of -1 means that medium is not known.
Currently, it is used to change the proxy_arp behavior:
the proxy_arp feature is enabled for packets forwarded between
two devices attached to different media.
proxy_arp - BOOLEAN Do proxy arp.
proxy_arp for the interface will be enabled if at least one of
conf/{all,interface}/proxy_arp is set to TRUE,
it will be disabled otherwise
shared_media - BOOLEAN Send(router) or accept(host) RFC1620 shared media redirects.
Overrides ip_secure_redirects.
shared_media for the interface will be enabled if at least one of
conf/{all,interface}/shared_media is set to TRUE,
it will be disabled otherwise
default TRUE
secure_redirects - BOOLEAN Accept ICMP redirect messages only for gateways,
listed in default gateway list.
secure_redirects for the interface will be enabled if at least one of conf/{all,interface}/secure_redirects is set to TRUE,
it will be disabled otherwise
default TRUE
send_redirects - BOOLEAN Send redirects, if router.
send_redirects for the interface will be enabled if at least one of conf/{all,interface}/send_redirects is set to TRUE,
it will be disabled otherwise
Default: TRUE
bootp_relay - BOOLEAN Accept packets with source address 0.b.c.d destined
not to this host as local ones. It is supposed, that
BOOTP relay daemon will catch and forward such packets.
conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay
for the interface
default FALSE
Not Implemented Yet.
accept_source_route - BOOLEAN Accept packets with SRR option.
conf/all/accept_source_route must also be set to TRUE to accept packets with SRR option on the interface
default TRUE (router) FALSE (host)
rp_filter - INTEGER 0 - No source validation. 1 - Strict mode as defined in RFC3704 Strict Reverse Path Each incoming packet is tested against the FIB and if the interface
is not the best reverse path the packet check will fail.
By default failed packets are discarded. 2 - Loose mode as defined in RFC3704 Loose Reverse Path Each incoming packet's source address is also tested against the FIB
and if the source address is not reachable via any interface
the packet check will fail.
Current recommended practice in RFC3704 is to enable strict mode
to prevent IP spoofing from DDos attacks. If using asymmetric routing or other complicated routing, then loose mode is recommended.
conf/all/rp_filter must also be set to non-zero to do source validation on the interface
Default value is 0. Note that some distributions enable it
in startup scripts.
arp_filter - BOOLEAN 1 - Allows you to have multiple network interfaces on the same
subnet, and have the ARPs for each interface be answered
based on whether or not the kernel would route a packet from
the ARP'd IP out that interface (therefore you must use source
based routing for this to work). In other words it allows control
of which cards (usually 1) will respond to an arp request.
0 - (default) The kernel can respond to arp requests with addresses from other interfaces. This may seem wrong but it usually makes
sense, because it increases the chance of successful communication.
IP addresses are owned by the complete host on Linux, not by
particular interfaces. Only for more complex setups like load- balancing, does this behaviour cause problems.
arp_filter for the interface will be enabled if at least one of
conf/{all,interface}/arp_filter is set to TRUE,
it will be disabled otherwise
arp_announce - INTEGER Define different restriction levels for announcing the local
source IP address from IP packets in ARP requests sent on
interface: 0 - (default) Use any local address, configured on any interface 1 - Try to avoid local addresses that are not in the target's
subnet for this interface. This mode is useful when target
hosts reachable via this interface require the source IP
address in ARP requests to be part of their logical network
configured on the receiving interface. When we generate the
request we will check all our subnets that include the
target IP and will preserve the source address if it is from
such subnet. If there is no such subnet we select source
address according to the rules for level 2. 2 - Always use the best local address for this target.
In this mode we ignore the source address in the IP packet
and try to select local address that we prefer for talks with
the target host. Such local address is selected by looking
for primary IP addresses on all our subnets on the outgoing
interface that include the target IP address. If no suitable
local address is found we select the first local address
we have on the outgoing interface or on all other interfaces,
with the hope we will receive reply for our request and
even sometimes no matter the source IP address we announce.
The max value from conf/{all,interface}/arp_announce is used.
Increasing the restriction level gives more chance for
receiving answer from the resolved target while decreasing
the level announces more valid sender's information.
arp_ignore - INTEGER Define different modes for sending replies in response to
received ARP requests that resolve local target IP addresses: 0 - (default): reply for any local target IP address, configured
on any interface 1 - reply only if the target IP address is local address
configured on the incoming interface 2 - reply only if the target IP address is local address
configured on the incoming interface and both with the
sender's IP address are part from same subnet on this interface 3 - do not reply for local addresses configured with scope host,
only resolutions for global and link addresses are replied 4-7 - reserved 8 - do not reply for all local addresses
The max value from conf/{all,interface}/arp_ignore is used
when ARP request is received on the {interface}
arp_notify - BOOLEAN Define mode for notification of address and device changes. 0 - (default): do nothing 1 - Generate gratuitous arp replies when device is brought up or hardware address changes.
arp_accept - BOOLEAN Define behavior when gratuitous arp replies are received: 0 - drop gratuitous arp frames 1 - accept gratuitous arp frames
app_solicit - INTEGER The maximum number of probes to send to the user space ARP daemon
via netlink before dropping back to multicast probes (see
mcast_solicit). Defaults to 0.
disable_policy - BOOLEAN Disable IPSEC policy (SPD) for this interface
disable_xfrm - BOOLEAN Disable IPSEC encryption on this interface, whatever the policy
tag - INTEGER Allows you to write a number, which can be used as required.
Default value is 0.
Alexey Kuznetsov. kuznet@ms2.inr.ac.ru
Updated by: Andi Kleen ak@muc.de Nicolas Delon delon.nicolas@wanadoo.fr
/proc/sys/net/ipv6/* Variables:
IPv6 has no global variables such as tcp_*. tcp_* settings under ipv4/ also apply to IPv6 [XXX?].
bindv6only - BOOLEAN Default value for IPV6_V6ONLY socket option,
which restricts use of the IPv6 socket to IPv6 communication
only. TRUE: disable IPv4-mapped address feature
FALSE: enable IPv4-mapped address feature
Default: FALSE (as specified in RFC2553bis)
IPv6 Fragmentation:
ip6frag_high_thresh - INTEGER Maximum memory used to reassemble IPv6 fragments. When ip6frag_high_thresh bytes of memory is allocated for this purpose,
the fragment handler will toss packets until ip6frag_low_thresh
is reached.
ip6frag_low_thresh - INTEGER See ip6frag_high_thresh
ip6frag_time - INTEGER Time in seconds to keep an IPv6 fragment in memory.
ip6frag_secret_interval - INTEGER Regeneration interval (in seconds) of the hash secret (or lifetime
for the hash secret) for IPv6 fragments.
Default: 600
conf/default/*: Change the interface-specific default settings.
conf/all/*: Change all the interface-specific settings.
[XXX: Other special features than forwarding?]
conf/all/forwarding - BOOLEAN Enable global IPv6 forwarding between all interfaces.
IPv4 and IPv6 work differently here; e.g. netfilter must be used
to control which interfaces may forward packets and which not.
This also sets all interfaces' Host/Router setting
'forwarding' to the specified value. See below for details.
This referred to as global forwarding.
proxy_ndp - BOOLEAN Do proxy ndp.
conf/interface/*: Change special settings per interface.
The functional behaviour for certain settings is different
depending on whether local forwarding is enabled or not.
accept_ra - BOOLEAN Accept Router Advertisements; autoconfigure using them.
Functional default: enabled if local forwarding is disabled. disabled if local forwarding is enabled.
accept_ra_defrtr - BOOLEAN Learn default router in Router Advertisement.
Functional default: enabled if accept_ra is enabled. disabled if accept_ra is disabled.
accept_ra_pinfo - BOOLEAN Learn Prefix Information in Router Advertisement.
Functional default: enabled if accept_ra is enabled. disabled if accept_ra is disabled.
accept_ra_rt_info_max_plen - INTEGER Maximum prefix length of Route Information in RA.
Route Information w/ prefix larger than or equal to this
variable shall be ignored.
Functional default: 0 if accept_ra_rtr_pref is enabled.
-1 if accept_ra_rtr_pref is disabled.
accept_ra_rtr_pref - BOOLEAN Accept Router Preference in RA.
Functional default: enabled if accept_ra is enabled. disabled if accept_ra is disabled.
accept_redirects - BOOLEAN Accept Redirects.
Functional default: enabled if local forwarding is disabled. disabled if local forwarding is enabled.
accept_source_route - INTEGER Accept source routing (routing extension header).
>= 0: Accept only routing header type 2.
< 0: Do not accept routing header.
Default: 0
autoconf - BOOLEAN Autoconfigure addresses using Prefix Information in Router Advertisements.
Functional default: enabled if accept_ra_pinfo is enabled. disabled if accept_ra_pinfo is disabled.
dad_transmits - INTEGER The amount of Duplicate Address Detection probes to send.
Default: 1
forwarding - BOOLEAN Configure interface-specific Host/Router behaviour.
Note: It is recommended to have the same setting on all
interfaces; mixed router/host scenarios are rather uncommon.
FALSE:
By default, Host behaviour is assumed. This means:
1. IsRouter flag is not set in Neighbour Advertisements.
2. Router Solicitations are being sent when necessary.
3. If accept_ra is TRUE (default), accept Router Advertisements (and do autoconfiguration).
4. If accept_redirects is TRUE (default), accept Redirects.
TRUE:
If local forwarding is enabled, Router behaviour is assumed.
This means exactly the reverse from the above:
1. IsRouter flag is set in Neighbour Advertisements.
2. Router Solicitations are not sent.
3. Router Advertisements are ignored.
4. Redirects are ignored.
Default: FALSE if global forwarding is disabled (default), otherwise TRUE.
hop_limit - INTEGER Default Hop Limit to set.
Default: 64
mtu - INTEGER Default Maximum Transfer Unit
Default: 1280 (IPv6 required minimum)
router_probe_interval - INTEGER Minimum interval (in seconds) between Router Probing described
in RFC4191.
Default: 60
router_solicitation_delay - INTEGER Number of seconds to wait after interface is brought up
before sending Router Solicitations.
Default: 1
router_solicitation_interval - INTEGER Number of seconds to wait between Router Solicitations.
Default: 4
router_solicitations - INTEGER Number of Router Solicitations to send until assuming no
routers are present.
Default: 3
use_tempaddr - INTEGER Preference for Privacy Extensions (RFC3041). <= 0 : disable Privacy Extensions
== 1 : enable Privacy Extensions, but prefer public addresses over temporary addresses. > 1 : enable Privacy Extensions and prefer temporary addresses over public addresses. Default: 0 (for most devices)
-1 (for point-to-point devices and loopback devices)
temp_valid_lft - INTEGER valid lifetime (in seconds) for temporary addresses.
Default: 604800 (7 days)
temp_prefered_lft - INTEGER Preferred lifetime (in seconds) for temporary addresses.
Default: 86400 (1 day)
max_desync_factor - INTEGER Maximum value for DESYNC_FACTOR, which is a random value
that ensures that clients don't synchronize with each
other and generate new addresses at exactly the same time.
value is in seconds.
Default: 600
regen_max_retry - INTEGER Number of attempts before give up attempting to generate
valid temporary addresses.
Default: 5
max_addresses - INTEGER Number of maximum addresses per interface. 0 disables limitation.
It is recommended not set too large value (or 0) because it would
be too easy way to crash kernel to allow to create too much of autoconfigured addresses.
Default: 16
disable_ipv6 - BOOLEAN Disable IPv6 operation. If accept_dad is set to 2, this value
will be dynamically set to TRUE if DAD fails for the link-local
address.
Default: FALSE (enable IPv6 operation)
When this value is changed from 1 to 0 (IPv6 is being enabled),
it will dynamically create a link-local address on the given
interface and start Duplicate Address Detection, if necessary.
When this value is changed from 0 to 1 (IPv6 is being disabled),
it will dynamically delete all address on the given interface.
accept_dad - INTEGER Whether to accept DAD (Duplicate Address Detection). 0: Disable DAD 1: Enable DAD (default) 2: Enable DAD, and disable IPv6 operation if MAC-based duplicate link-local address has been found.
icmp/*: ratelimit - INTEGER Limit the maximal rates for sending ICMPv6 packets. 0 to disable any limiting,
otherwise the minimal space between responses in milliseconds.
Default: 1000
IPv6 Update by: Pekka Savola <pekkas@netcore.fi> YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org>
/proc/sys/net/bridge/* Variables:
bridge-nf-call-arptables - BOOLEAN 1 : pass bridged ARP traffic to arptables' FORWARD chain. 0 : disable this.
Default: 1
bridge-nf-call-iptables - BOOLEAN 1 : pass bridged IPv4 traffic to iptables' chains. 0 : disable this.
Default: 1
bridge-nf-call-ip6tables - BOOLEAN 1 : pass bridged IPv6 traffic to ip6tables' chains. 0 : disable this.
Default: 1
bridge-nf-filter-vlan-tagged - BOOLEAN 1 : pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables. 0 : disable this.
Default: 1
bridge-nf-filter-pppoe-tagged - BOOLEAN 1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables. 0 : disable this.
Default: 1
proc/sys/net/sctp/* Variables:
addip_enable - BOOLEAN Enable or disable extension of Dynamic Address Reconfiguration
(ADD-IP) functionality specified in RFC5061. This extension provides the ability to dynamically add and remove new addresses for the SCTP associations.
1: Enable extension.
0: Disable extension.
Default: 0
addip_noauth_enable - BOOLEAN Dynamic Address Reconfiguration (ADD-IP) requires the use of authentication to protect the operations of adding or removing new addresses. This requirement is mandated so that unauthorized hosts would not be able to hijack associations. However, older implementations may not have implemented this requirement while
allowing the ADD-IP extension. For reasons of interoperability,
we provide this variable to control the enforcement of the authentication requirement.
1: Allow ADD-IP extension to be used without authentication. This should only be set in a closed environment for interoperability
with older implementations.
0: Enforce the authentication requirement
Default: 0
auth_enable - BOOLEAN Enable or disable Authenticated Chunks extension. This extension provides the ability to send and receive authenticated chunks and is required for secure operation of Dynamic Address Reconfiguration
(ADD-IP) extension.
1: Enable this extension. 0: Disable this extension.
Default: 0
prsctp_enable - BOOLEAN Enable or disable the Partial Reliability extension (RFC3758) which
is used to notify peers that a given DATA should no longer be expected.
1: Enable extension 0: Disable
Default: 1
max_burst - INTEGER The limit of the number of new packets that can be initially sent. It controls how bursty the generated traffic can be.
Default: 4
association_max_retrans - INTEGER Set the maximum number for retransmissions that an association can attempt deciding that the remote end is unreachable. If this value
is exceeded, the association is terminated.
Default: 10
max_init_retransmits - INTEGER The maximum number of retransmissions of INIT and COOKIE-ECHO chunks that an association will attempt before declaring the destination unreachable and terminating.
Default: 8
path_max_retrans - INTEGER The maximum number of retransmissions that will be attempted on a given path. Once this threshold is exceeded, the path is considered unreachable, and new traffic will use a different path when the association is multihomed.
Default: 5
rto_initial - INTEGER The initial round trip timeout value in milliseconds that will be used in calculating round trip times. This is the initial time interval
for retransmissions.
Default: 3000
rto_max - INTEGER The maximum value (in milliseconds) of the round trip timeout. This
is the largest time interval that can elapse between retransmissions.
Default: 60000
rto_min - INTEGER The minimum value (in milliseconds) of the round trip timeout. This
is the smallest time interval the can elapse between retransmissions.
Default: 1000
hb_interval - INTEGER The interval (in milliseconds) between HEARTBEAT chunks. These chunks are sent at the specified interval on idle paths to probe the state of
a given path between 2 associations.
Default: 30000
sack_timeout - INTEGER The amount of time (in milliseconds) that the implementation will wait to send a SACK.
Default: 200
valid_cookie_life - INTEGER The default lifetime of the SCTP cookie (in milliseconds). The cookie is used during association establishment.
Default: 60000
cookie_preserve_enable - BOOLEAN Enable or disable the ability to extend the lifetime of the SCTP cookie that is used during the establishment phase of SCTP association
1: Enable cookie lifetime extension. 0: Disable
Default: 1
rcvbuf_policy - INTEGER Determines if the receive buffer is attributed to the socket or to association. SCTP supports the capability to create multiple associations on a single socket. When using this capability, it is possible that a single stalled association that's buffering a lot
of data may block other associations from delivering their data by consuming all of the receive buffer space. To work around this,
the rcvbuf_policy could be set to attribute the receiver buffer space to each association instead of the socket. This prevents the described blocking.
1: rcvbuf space is per association 0: recbuf space is per socket
Default: 0
sndbuf_policy - INTEGER Similar to rcvbuf_policy above, this applies to send buffer space.
1: Send buffer is tracked per association 0: Send buffer is tracked per socket.
Default: 0
sctp_mem - vector of 3 INTEGERs: min, pressure, max Number of pages allowed for queueing by all SCTP sockets.
min: Below this number of pages SCTP is not bothered about its
memory appetite. When amount of memory allocated by SCTP exceeds
this number, SCTP starts to moderate memory usage.
pressure: This value was introduced to follow format of tcp_mem.
max: Number of pages allowed for queueing by all SCTP sockets.
Default is calculated at boot time from amount of available memory.
sctp_rmem - vector of 3 INTEGERs: min, default, max See tcp_rmem for a description.
sctp_wmem - vector of 3 INTEGERs: min, default, max See tcp_wmem for a description.
addr_scope_policy - INTEGER Control IPv4 address scoping - draft-stewart-tsvwg-sctp-ipv4-00
0 - Disable IPv4 address scoping 1 - Enable IPv4 address scoping 2 - Follow draft but allow IPv4 private addresses 3 - Follow draft but allow IPv4 link local addresses
Default: 1
/proc/sys/net/core/* dev_weight - INTEGER The maximum number of packets that kernel can handle on a NAPI
interrupt, it's a Per-CPU variable.
Default: 64
/proc/sys/net/unix/* max_dgram_qlen - INTEGER The maximum length of dgram socket receive queue
Default: 10
UNDOCUMENTED:
/proc/sys/net/irda/* fast_poll_increase FIXME
warn_noreply_time FIXME
discovery_slots FIXME
slot_timeout FIXME
max_baud_rate FIXME
discovery_timeout FIXME
lap_keepalive_time FIXME
max_noreply_time FIXME
max_tx_data_size FIXME
max_tx_window FIXME
min_tx_turn_time FIXME
ip_forward - BOOLEAN 0 - disabled (default)
not 0 - enabled
Forward Packets between interfaces.
This variable is special, its change resets all configuration parameters to their default state (RFC1122 for hosts, RFC1812
for routers)
ip_default_ttl - INTEGER default 64
ip_no_pmtu_disc - BOOLEAN Disable Path MTU Discovery.
default FALSE
min_pmtu - INTEGER default 562 - minimum discovered Path MTU
mtu_expires - INTEGER Time, in seconds, that cached PMTU information is kept.
min_adv_mss - INTEGER The advertised MSS depends on the first hop route MTU, but will
never be lower than this setting.
rt_cache_rebuild_count - INTEGER The per net-namespace route cache emergency rebuild threshold.
Any net-namespace having its route cache rebuilt due to
a hash bucket chain being too long more than this many times
will have its route caching disabled
IP Fragmentation:
ipfrag_high_thresh - INTEGER Maximum memory used to reassemble IP fragments. When
ipfrag_high_thresh bytes of memory is allocated for this purpose,
the fragment handler will toss packets until ipfrag_low_thresh
is reached.
ipfrag_low_thresh - INTEGER See ipfrag_high_thresh
ipfrag_time - INTEGER Time in seconds to keep an IP fragment in memory.
ipfrag_secret_interval - INTEGER Regeneration interval (in seconds) of the hash secret (or lifetime
for the hash secret) for IP fragments.
Default: 600
ipfrag_max_dist - INTEGER ipfrag_max_dist is a non-negative integer value which defines the maximum "disorder" which is allowed among fragments which share a
common IP source address. Note that reordering of packets is
not unusual, but if a large number of fragments arrive from a source
IP address while a particular fragment queue remains incomplete, it probably indicates that one or more fragments belonging to that queue have been lost. When ipfrag_max_dist is positive, an additional check
is done on fragments before they are added to a reassembly queue - if ipfrag_max_dist (or more) fragments have arrived from a particular IP address between additions to any IP fragment queue using that source address, it's presumed that one or more fragments in the queue are
lost. The existing fragment queue will be dropped, and a new one started. An ipfrag_max_dist value of zero disables this check.
Using a very small value, e.g. 1 or 2, for ipfrag_max_dist can
result in unnecessarily dropping fragment queues when normal
reordering of packets occurs, which could lead to poor application performance. Using a very large value, e.g. 50000, increases the likelihood of incorrectly reassembling IP fragments that originate
from different IP datagrams, which could result in data corruption. Default: 64
INET peer storage:
inet_peer_threshold - INTEGER The approximate size of the storage. Starting from this threshold entries will be thrown aggressively. This threshold also determines entries' time-to-live and time intervals between garbage collection passes. More entries, less time-to-live, less GC interval.
inet_peer_minttl - INTEGER Minimum time-to-live of entries. Should be enough to cover fragment time-to-live on the reassembling side. This minimum time-to-live is guaranteed if the pool size is less than inet_peer_threshold.
Measured in seconds.
inet_peer_maxttl - INTEGER Maximum time-to-live of entries. Unused entries will expire after
this period of time if there is no memory pressure on the pool (i.e. when the number of entries in the pool is very small).
Measured in seconds.
inet_peer_gc_mintime - INTEGER Minimum interval between garbage collection passes. This interval is
in effect under high memory pressure on the pool.
Measured in seconds.
inet_peer_gc_maxtime - INTEGER Minimum interval between garbage collection passes. This interval is
in effect under low (or absent) memory pressure on the pool.
Measured in seconds.
TCP variables:
somaxconn - INTEGER Limit of socket listen() backlog, known in userspace as SOMAXCONN. Defaults to 128. See also tcp_max_syn_backlog for additional tuning
for TCP sockets.
tcp_abc - INTEGER Controls Appropriate Byte Count (ABC) defined in RFC3465.
ABC is a way of increasing congestion window (cwnd) more slowly
in response to partial acknowledgments.
Possible values are: 0 increase cwnd once per acknowledgment (no ABC) 1 increase cwnd once per acknowledgment of full sized segment 2 allow increase cwnd by two if acknowledgment is of two segments to compensate for delayed acknowledgments. Default: 0 (off)
tcp_abort_on_overflow - BOOLEAN If listening service is too slow to accept new connections,
reset them. Default state is FALSE. It means that if overflow
occurred due to a burst, connection will recover. Enable this
option _only_ if you are really sure that listening daemon
cannot be tuned to accept connections faster. Enabling this
option can harm clients of your server.
tcp_adv_win_scale - INTEGER Count buffering overhead as bytes/2^tcp_adv_win_scale
(if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale),
if it is <= 0.
Default: 2
tcp_allowed_congestion_control - STRING Show/set the congestion control choices available to non-privileged processes. The list is a subset of those listed in tcp_available_congestion_control.
Default is "reno" and the default setting (tcp_congestion_control).
tcp_app_win - INTEGER Reserve max(window/2^tcp_app_win, mss) of window for application
buffer. Value 0 is special, it means that nothing is reserved.
Default: 31
tcp_available_congestion_control - STRING Shows the available congestion control choices that are registered.
More congestion control algorithms may be available as modules,
but not loaded.
tcp_base_mss - INTEGER The initial value of search_low to be used by the packetization layer Path MTU discovery (MTU probing). If MTU probing is enabled,
this is the initial MSS used by the connection.
tcp_congestion_control - STRING Set the congestion control algorithm to be used for new
connections. The algorithm "reno" is always available, but
additional choices may be available based on kernel configuration. Default is set as part of kernel configuration.
tcp_dsack - BOOLEAN Allows TCP to send "duplicate" SACKs.
tcp_ecn - BOOLEAN Enable Explicit Congestion Notification (ECN) in TCP. ECN is only
used when both ends of the TCP flow support it. It is useful to
avoid losses due to congestion (when the bottleneck router supports
ECN).
Possible values are: 0 disable ECN 1 ECN enabled 2 Only server-side ECN enabled. If the other end does not support ECN, behavior is like with ECN disabled. Default: 2
tcp_fack - BOOLEAN Enable FACK congestion avoidance and fast retransmission.
The value is not used, if tcp_sack is not enabled.
tcp_fin_timeout - INTEGER Time to hold socket in state FIN-WAIT-2, if it was closed
by our side. Peer can be broken and never close its side,
or even died unexpectedly. Default value is 60sec.
Usual value used in 2.2 was 180 seconds, you may restore
it, but remember that if your machine is even underloaded WEB server, you risk to overflow memory with kilotons of dead sockets,
FIN-WAIT-2 sockets are less dangerous than FIN-WAIT-1,
because they eat maximum 1.5K of memory, but they tend
to live longer. Cf. tcp_max_orphans.
tcp_frto - INTEGER Enables Forward RTO-Recovery (F-RTO) defined in RFC4138.
F-RTO is an enhanced recovery algorithm for TCP retransmission
timeouts. It is particularly beneficial in wireless environments
where packet loss is typically due to random radio interference
rather than intermediate router congestion. F-RTO is sender-side
only modification. Therefore it does not require any support from
the peer.
If set to 1, basic version is enabled. 2 enables SACK enhanced
F-RTO if flow uses SACK. The basic version can be used also when
SACK is in use though scenario(s) with it exists where F-RTO
interacts badly with the packet counting of the SACK enabled TCP
flow.
tcp_frto_response - INTEGER When F-RTO has detected that a TCP retransmission timeout was
spurious (i.e, the timeout would have been avoided had TCP set a
longer retransmission timeout), TCP has several options what to do
next. Possible values are: 0 Rate halving based; a smooth and conservative response, results in halved cwnd and ssthresh after one RTT 1 Very conservative response; not recommended because even though being valid, it interacts poorly with the rest of
Linux TCP, halves cwnd and ssthresh immediately 2 Aggressive response; undoes congestion control measures that are now known to be unnecessary (ignoring the
possibility of a lost retransmission that would require
TCP to be more cautious), cwnd and ssthresh are restored
to the values prior timeout Default: 0 (rate halving based)
tcp_keepalive_time - INTEGER How often TCP sends out keepalive messages when keepalive is enabled. Default: 2hours.
tcp_keepalive_probes - INTEGER How many keepalive probes TCP sends out, until it decides that the connection is broken. Default value: 9.
tcp_keepalive_intvl - INTEGER How frequently the probes are send out. Multiplied by tcp_keepalive_probes it is time to kill not responding connection,
after probes started. Default value: 75sec i.e. connection
will be aborted after ~11 minutes of retries.
tcp_low_latency - BOOLEAN If set, the TCP stack makes decisions that prefer lower
latency as opposed to higher throughput. By default, this
option is not set meaning that higher throughput is preferred.
An example of an application where this default should be
changed would be a Beowulf compute cluster.
Default: 0
tcp_max_orphans - INTEGER Maximal number of TCP sockets not attached to any user file handle,
held by system. If this number is exceeded orphaned connections are reset immediately and warning is printed. This limit exists
only to prevent simple DoS attacks, you _must_ not rely on this
or lower the limit artificially, but rather increase it
(probably, after increasing installed memory),
if network conditions require more than default value,
and tune network services to linger and kill such states
more aggressively. Let me to remind again: each orphan eats
up to ~64K of unswappable memory.
tcp_max_syn_backlog - INTEGER Maximal number of remembered connection requests, which are
still did not receive an acknowledgment from connecting client.
Default value is 1024 for systems with more than 128Mb of memory,
and 128 for low memory machines. If server suffers of overload,
try to increase this number.
tcp_max_tw_buckets - INTEGER Maximal number of timewait sockets held by system simultaneously.
If this number is exceeded time-wait socket is immediately destroyed and warning is printed. This limit exists only to prevent
simple DoS attacks, you _must_ not lower the limit artificially,
but rather increase it (probably, after increasing installed memory), if network conditions require more than default value.
tcp_mem - vector of 3 INTEGERs: min, pressure, max min: below this number of pages TCP is not bothered about its
memory appetite.
pressure: when amount of memory allocated by TCP exceeds this number
of pages, TCP moderates its memory consumption and enters memory pressure mode, which is exited when memory consumption falls
under "min".
max: number of pages allowed for queueing by all TCP sockets.
Defaults are calculated at boot time from amount of available
memory.
tcp_moderate_rcvbuf - BOOLEAN If set, TCP performs receive buffer auto-tuning, attempting to automatically size the buffer (no greater than tcp_rmem[2]) to
match the size required by the path for full throughput. Enabled by default.
tcp_mtu_probing - INTEGER Controls TCP Packetization-Layer Path MTU Discovery. Takes three
values: 0 - Disabled 1 - Disabled by default, enabled when an ICMP black hole detected 2 - Always enabled, use initial MSS of tcp_base_mss.
tcp_no_metrics_save - BOOLEAN By default, TCP saves various connection metrics in the route cache
when the connection closes, so that connections established in the
near future can use these to set initial conditions. Usually, this increases overall performance, but may sometimes cause performance degradation. If set, TCP will not cache metrics on closing
connections.
tcp_orphan_retries - INTEGER This value influences the timeout of a locally closed TCP connection, when RTO retransmissions remain unacknowledged.
See tcp_retries2 for more details.
The default value is 7.
If your machine is a loaded WEB server,
you should think about lowering this value, such sockets
may consume significant resources. Cf. tcp_max_orphans.
tcp_reordering - INTEGER Maximal reordering of packets in a TCP stream.
Default: 3
tcp_retrans_collapse - BOOLEAN Bug-to-bug compatibility with some broken printers.
On retransmit try to send bigger packets to work around bugs in
certain TCP stacks.
tcp_retries1 - INTEGER This value influences the time, after which TCP decides, that
something is wrong due to unacknowledged RTO retransmissions,
and reports this suspicion to the network layer.
See tcp_retries2 for more details.
RFC 1122 recommends at least 3 retransmissions, which is the
default.
tcp_retries2 - INTEGER This value influences the timeout of an alive TCP connection,
when RTO retransmissions remain unacknowledged.
Given a value of N, a hypothetical TCP connection following
exponential backoff with an initial RTO of TCP_RTO_MIN would
retransmit N times before killing the connection at the (N+1)th RTO.
The default value of 15 yields a hypothetical timeout of 924.6
seconds and is a lower bound for the effective timeout.
TCP will effectively time out at the first RTO which exceeds the hypothetical timeout.
RFC 1122 recommends at least 100 seconds for the timeout,
which corresponds to a value of at least 8.
tcp_rfc1337 - BOOLEAN If set, the TCP stack behaves conforming to RFC1337. If unset,
we are not conforming to RFC, but prevent TCP TIME_WAIT
assassination.
Default: 0
tcp_rmem - vector of 3 INTEGERs: min, default, max min: Minimal size of receive buffer used by TCP sockets.
It is guaranteed to each TCP socket, even under moderate memory pressure.
Default: 8K
default: initial size of receive buffer used by TCP sockets.
This value overrides net.core.rmem_default used by other protocols. Default: 87380 bytes. This value results in window of 65535 with
default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit
less for default tcp_app_win. See below about these variables.
max: maximal size of receive buffer allowed for automatically
selected receiver buffers for TCP socket. This value does not override net.core.rmem_max. Calling setsockopt() with SO_RCVBUF disables automatic tuning of that socket's receive buffer size, in which
case this value is ignored.
Default: between 87380B and 4MB, depending on RAM size.
tcp_sack - BOOLEAN Enable select acknowledgments (SACKS).
tcp_slow_start_after_idle - BOOLEAN If set, provide RFC2861 behavior and time out the congestion
window after an idle period. An idle period is defined at
the current RTO. If unset, the congestion window will not
be timed out after an idle period.
Default: 1
tcp_stdurg - BOOLEAN Use the Host requirements interpretation of the TCP urgent pointer field. Most hosts use the older BSD interpretation, so if you turn this on Linux might not communicate correctly with them.
Default: FALSE
tcp_synack_retries - INTEGER Number of times SYNACKs for a passive TCP connection attempt will
be retransmitted. Should not be higher than 255. Default value
is 5, which corresponds to ~180seconds.
tcp_syncookies - BOOLEAN Only valid when the kernel was compiled with CONFIG_SYNCOOKIES
Send out syncookies when the syn backlog queue of a socket
overflows. This is to prevent against the common 'SYN flood attack' Default: FALSE
Note, that syncookies is fallback facility.
It MUST NOT be used to help highly loaded servers to stand
against legal connection rate. If you see SYN flood warnings
in your logs, but investigation shows that they occur
because of overload with legal connections, you should tune
another parameters until this warning disappear.
See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow.
syncookies seriously violate TCP protocol, do not allow
to use TCP extensions, can result in serious degradation
of some services (f.e. SMTP relaying), visible not by you,
but your clients and relays, contacting you. While you see
SYN flood warnings in logs not being really flooded, your server
is seriously misconfigured.
tcp_syn_retries - INTEGER Number of times initial SYNs for an active TCP connection attempt
will be retransmitted. Should not be higher than 255. Default value
is 5, which corresponds to ~180seconds.
tcp_timestamps - BOOLEAN Enable timestamps as defined in RFC1323.
tcp_tso_win_divisor - INTEGER This allows control over what percentage of the congestion window
can be consumed by a single TSO frame.
The setting of this parameter is a choice between burstiness and building larger TSO frames.
Default: 3
tcp_tw_recycle - BOOLEAN Enable fast recycling TIME-WAIT sockets. Default value is 0.
It should not be changed without advice/request of technical
experts.
tcp_tw_reuse - BOOLEAN Allow to reuse TIME-WAIT sockets for new connections when it is
safe from protocol viewpoint. Default value is 0.
It should not be changed without advice/request of technical
experts.
tcp_window_scaling - BOOLEAN Enable window scaling as defined in RFC1323.
tcp_wmem - vector of 3 INTEGERs: min, default, max min: Amount of memory reserved for send buffers for TCP sockets.
Each TCP socket has rights to use it due to fact of its birth.
Default: 4K
default: initial size of send buffer used by TCP sockets. This
value overrides net.core.wmem_default used by other protocols.
It is usually lower than net.core.wmem_default.
Default: 16K
max: Maximal amount of memory allowed for automatically tuned
send buffers for TCP sockets. This value does not override
net.core.wmem_max. Calling setsockopt() with SO_SNDBUF disables automatic tuning of that socket's send buffer size, in which case
this value is ignored.
Default: between 64K and 4MB, depending on RAM size.
tcp_workaround_signed_windows - BOOLEAN If set, assume no receipt of a window scaling option means the
remote TCP is broken and treats the window as a signed quantity.
If unset, assume the remote TCP is not broken even if we do
not receive a window scaling option from them.
Default: 0
tcp_dma_copybreak - INTEGER Lower limit, in bytes, of the size of socket reads that will be offloaded to a DMA copy engine, if one is present in the system
and CONFIG_NET_DMA is enabled.
Default: 4096
UDP variables:
udp_mem - vector of 3 INTEGERs: min, pressure, max Number of pages allowed for queueing by all UDP sockets.
min: Below this number of pages UDP is not bothered about its
memory appetite. When amount of memory allocated by UDP exceeds
this number, UDP starts to moderate memory usage.
pressure: This value was introduced to follow format of tcp_mem.
max: Number of pages allowed for queueing by all UDP sockets.
Default is calculated at boot time from amount of available memory.
udp_rmem_min - INTEGER Minimal size of receive buffer used by UDP sockets in moderation.
Each UDP socket is able to use the size for receiving data, even if total pages of UDP sockets exceed udp_mem pressure. The unit is byte. Default: 4096
udp_wmem_min - INTEGER Minimal size of send buffer used by UDP sockets in moderation.
Each UDP socket is able to use the size for sending data, even if
total pages of UDP sockets exceed udp_mem pressure. The unit is byte. Default: 4096
CIPSOv4 Variables:
cipso_cache_enable - BOOLEAN If set, enable additions to and lookups from the CIPSO label mapping cache. If unset, additions are ignored and lookups always result in a miss. However, regardless of the setting the cache is still
invalidated when required when means you can safely toggle this on and off and the cache will always be "safe".
Default: 1
cipso_cache_bucket_size - INTEGER The CIPSO label cache consists of a fixed size hash table with each
hash bucket containing a number of cache entries. This variable limits the number of entries in each hash bucket; the larger the value the
more CIPSO label mappings that can be cached. When the number of entries in a given hash bucket reaches this limit adding new entries causes the oldest entry in the bucket to be removed to make room. Default: 10
cipso_rbm_optfmt - BOOLEAN Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of
the CIPSO draft specification (see Documentation/netlabel for details). This means that when set the CIPSO tag will be padded with empty categories in order to make the packet data 32-bit aligned.
Default: 0
cipso_rbm_structvalid - BOOLEAN If set, do a very strict check of the CIPSO option when ip_options_compile() is called. If unset, relax the checks done during ip_options_compile(). Either way is "safe" as errors are caught else where in the CIPSO processing code but setting this to 0 (False) should result in less work (i.e. it should be faster) but could cause problems with other implementations that require strict checking.
Default: 0
IP Variables:
ip_local_port_range - 2 INTEGERS Defines the local port range that is used by TCP and UDP to
choose the local port. The first number is the first, the
second the last local port number. Default value depends on
amount of memory available on the system:
> 128Mb 32768-61000
< 128Mb 1024-4999 or even less.
This number defines number of active connections, which this
system can issue simultaneously to systems not supporting
TCP extensions (timestamps). With tcp_tw_recycle enabled
(i.e. by default) range 1024-4999 is enough to issue up to 2000 connections per second to systems supporting timestamps.
ip_nonlocal_bind - BOOLEAN If set, allows processes to bind() to non-local IP addresses,
which can be quite useful - but may break some applications.
Default: 0
ip_dynaddr - BOOLEAN If set non-zero, enables support for dynamic addresses.
If set to a non-zero value larger than 1, a kernel log
message will be printed when dynamic address rewriting
occurs.
Default: 0
icmp_echo_ignore_all - BOOLEAN If set non-zero, then the kernel will ignore all ICMP ECHO
requests sent to it.
Default: 0
icmp_echo_ignore_broadcasts - BOOLEAN If set non-zero, then the kernel will ignore all ICMP ECHO and
TIMESTAMP requests sent to it via broadcast/multicast.
Default: 1
icmp_ratelimit - INTEGER Limit the maximal rates for sending ICMP packets whose type matches icmp_ratemask (see below) to specific targets. 0 to disable any limiting,
otherwise the minimal space between responses in milliseconds.
Default: 1000
icmp_ratemask - INTEGER Mask made of ICMP types for which rates are being limited.
Significant bits: IHGFEDCBA9876543210
Default mask: 0000001100000011000 (6168)
Bit definitions (see include/linux/icmp.h): 0 Echo Reply 3 Destination Unreachable * 4 Source Quench * 5 Redirect 8 Echo Request
B Time Exceeded *
C Parameter Problem *
D Timestamp Request
E Timestamp Reply
F Info Request
G Info Reply
H Address Mask Request
I Address Mask Reply
* These are rate limited by default (see default mask above)
icmp_ignore_bogus_error_responses - BOOLEAN Some routers violate RFC1122 by sending bogus responses to broadcast frames. Such violations are normally logged via a kernel warning.
If this is set to TRUE, the kernel will not give such warnings, which will avoid log file clutter.
Default: FALSE
icmp_errors_use_inbound_ifaddr - BOOLEAN
If zero, icmp error messages are sent with the primary address of
the exiting interface.
If non-zero, the message will be sent with the primary address of
the interface that received the packet that caused the icmp error.
This is the behaviour network many administrators will expect from
a router. And it can make debugging complicated network layouts
much easier.
Note that if no primary address exists for the interface selected,
then the primary address of the first non-loopback interface that
has one will be used regardless of this setting.
Default: 0
igmp_max_memberships - INTEGER Change the maximum number of multicast groups we can subscribe to. Default: 20
conf/interface/* changes special settings per interface (where "interface" is the name of your network interface) conf/all/* is special, changes the settings for all interfaces
log_martians - BOOLEAN Log packets with impossible addresses to kernel log.
log_martians for the interface will be enabled if at least one of
conf/{all,interface}/log_martians is set to TRUE,
it will be disabled otherwise
accept_redirects - BOOLEAN Accept ICMP redirect messages.
accept_redirects for the interface will be enabled if:
- both conf/{all,interface}/accept_redirects are TRUE in the case forwarding for the interface is enabled or
- at least one of conf/{all,interface}/accept_redirects is TRUE in the case forwarding for the interface is disabled accept_redirects for the interface will be disabled otherwise
default TRUE (host) FALSE (router)
forwarding - BOOLEAN Enable IP forwarding on this interface.
mc_forwarding - BOOLEAN Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE and a multicast routing daemon is required.
conf/all/mc_forwarding must also be set to TRUE to enable multicast routing for the interface
medium_id - INTEGER Integer value used to differentiate the devices by the medium they
are attached to. Two devices can have different id values when
the broadcast packets are received only on one of them.
The default value 0 means that the device is the only interface
to its medium, value of -1 means that medium is not known.
Currently, it is used to change the proxy_arp behavior:
the proxy_arp feature is enabled for packets forwarded between
two devices attached to different media.
proxy_arp - BOOLEAN Do proxy arp.
proxy_arp for the interface will be enabled if at least one of
conf/{all,interface}/proxy_arp is set to TRUE,
it will be disabled otherwise
shared_media - BOOLEAN Send(router) or accept(host) RFC1620 shared media redirects.
Overrides ip_secure_redirects.
shared_media for the interface will be enabled if at least one of
conf/{all,interface}/shared_media is set to TRUE,
it will be disabled otherwise
default TRUE
secure_redirects - BOOLEAN Accept ICMP redirect messages only for gateways,
listed in default gateway list.
secure_redirects for the interface will be enabled if at least one of conf/{all,interface}/secure_redirects is set to TRUE,
it will be disabled otherwise
default TRUE
send_redirects - BOOLEAN Send redirects, if router.
send_redirects for the interface will be enabled if at least one of conf/{all,interface}/send_redirects is set to TRUE,
it will be disabled otherwise
Default: TRUE
bootp_relay - BOOLEAN Accept packets with source address 0.b.c.d destined
not to this host as local ones. It is supposed, that
BOOTP relay daemon will catch and forward such packets.
conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay
for the interface
default FALSE
Not Implemented Yet.
accept_source_route - BOOLEAN Accept packets with SRR option.
conf/all/accept_source_route must also be set to TRUE to accept packets with SRR option on the interface
default TRUE (router) FALSE (host)
rp_filter - INTEGER 0 - No source validation. 1 - Strict mode as defined in RFC3704 Strict Reverse Path Each incoming packet is tested against the FIB and if the interface
is not the best reverse path the packet check will fail.
By default failed packets are discarded. 2 - Loose mode as defined in RFC3704 Loose Reverse Path Each incoming packet's source address is also tested against the FIB
and if the source address is not reachable via any interface
the packet check will fail.
Current recommended practice in RFC3704 is to enable strict mode
to prevent IP spoofing from DDos attacks. If using asymmetric routing or other complicated routing, then loose mode is recommended.
conf/all/rp_filter must also be set to non-zero to do source validation on the interface
Default value is 0. Note that some distributions enable it
in startup scripts.
arp_filter - BOOLEAN 1 - Allows you to have multiple network interfaces on the same
subnet, and have the ARPs for each interface be answered
based on whether or not the kernel would route a packet from
the ARP'd IP out that interface (therefore you must use source
based routing for this to work). In other words it allows control
of which cards (usually 1) will respond to an arp request.
0 - (default) The kernel can respond to arp requests with addresses from other interfaces. This may seem wrong but it usually makes
sense, because it increases the chance of successful communication.
IP addresses are owned by the complete host on Linux, not by
particular interfaces. Only for more complex setups like load- balancing, does this behaviour cause problems.
arp_filter for the interface will be enabled if at least one of
conf/{all,interface}/arp_filter is set to TRUE,
it will be disabled otherwise
arp_announce - INTEGER Define different restriction levels for announcing the local
source IP address from IP packets in ARP requests sent on
interface: 0 - (default) Use any local address, configured on any interface 1 - Try to avoid local addresses that are not in the target's
subnet for this interface. This mode is useful when target
hosts reachable via this interface require the source IP
address in ARP requests to be part of their logical network
configured on the receiving interface. When we generate the
request we will check all our subnets that include the
target IP and will preserve the source address if it is from
such subnet. If there is no such subnet we select source
address according to the rules for level 2. 2 - Always use the best local address for this target.
In this mode we ignore the source address in the IP packet
and try to select local address that we prefer for talks with
the target host. Such local address is selected by looking
for primary IP addresses on all our subnets on the outgoing
interface that include the target IP address. If no suitable
local address is found we select the first local address
we have on the outgoing interface or on all other interfaces,
with the hope we will receive reply for our request and
even sometimes no matter the source IP address we announce.
The max value from conf/{all,interface}/arp_announce is used.
Increasing the restriction level gives more chance for
receiving answer from the resolved target while decreasing
the level announces more valid sender's information.
arp_ignore - INTEGER Define different modes for sending replies in response to
received ARP requests that resolve local target IP addresses: 0 - (default): reply for any local target IP address, configured
on any interface 1 - reply only if the target IP address is local address
configured on the incoming interface 2 - reply only if the target IP address is local address
configured on the incoming interface and both with the
sender's IP address are part from same subnet on this interface 3 - do not reply for local addresses configured with scope host,
only resolutions for global and link addresses are replied 4-7 - reserved 8 - do not reply for all local addresses
The max value from conf/{all,interface}/arp_ignore is used
when ARP request is received on the {interface}
arp_notify - BOOLEAN Define mode for notification of address and device changes. 0 - (default): do nothing 1 - Generate gratuitous arp replies when device is brought up or hardware address changes.
arp_accept - BOOLEAN Define behavior when gratuitous arp replies are received: 0 - drop gratuitous arp frames 1 - accept gratuitous arp frames
app_solicit - INTEGER The maximum number of probes to send to the user space ARP daemon
via netlink before dropping back to multicast probes (see
mcast_solicit). Defaults to 0.
disable_policy - BOOLEAN Disable IPSEC policy (SPD) for this interface
disable_xfrm - BOOLEAN Disable IPSEC encryption on this interface, whatever the policy
tag - INTEGER Allows you to write a number, which can be used as required.
Default value is 0.
Alexey Kuznetsov. kuznet@ms2.inr.ac.ru
Updated by: Andi Kleen ak@muc.de Nicolas Delon delon.nicolas@wanadoo.fr
/proc/sys/net/ipv6/* Variables:
IPv6 has no global variables such as tcp_*. tcp_* settings under ipv4/ also apply to IPv6 [XXX?].
bindv6only - BOOLEAN Default value for IPV6_V6ONLY socket option,
which restricts use of the IPv6 socket to IPv6 communication
only. TRUE: disable IPv4-mapped address feature
FALSE: enable IPv4-mapped address feature
Default: FALSE (as specified in RFC2553bis)
IPv6 Fragmentation:
ip6frag_high_thresh - INTEGER Maximum memory used to reassemble IPv6 fragments. When ip6frag_high_thresh bytes of memory is allocated for this purpose,
the fragment handler will toss packets until ip6frag_low_thresh
is reached.
ip6frag_low_thresh - INTEGER See ip6frag_high_thresh
ip6frag_time - INTEGER Time in seconds to keep an IPv6 fragment in memory.
ip6frag_secret_interval - INTEGER Regeneration interval (in seconds) of the hash secret (or lifetime
for the hash secret) for IPv6 fragments.
Default: 600
conf/default/*: Change the interface-specific default settings.
conf/all/*: Change all the interface-specific settings.
[XXX: Other special features than forwarding?]
conf/all/forwarding - BOOLEAN Enable global IPv6 forwarding between all interfaces.
IPv4 and IPv6 work differently here; e.g. netfilter must be used
to control which interfaces may forward packets and which not.
This also sets all interfaces' Host/Router setting
'forwarding' to the specified value. See below for details.
This referred to as global forwarding.
proxy_ndp - BOOLEAN Do proxy ndp.
conf/interface/*: Change special settings per interface.
The functional behaviour for certain settings is different
depending on whether local forwarding is enabled or not.
accept_ra - BOOLEAN Accept Router Advertisements; autoconfigure using them.
Functional default: enabled if local forwarding is disabled. disabled if local forwarding is enabled.
accept_ra_defrtr - BOOLEAN Learn default router in Router Advertisement.
Functional default: enabled if accept_ra is enabled. disabled if accept_ra is disabled.
accept_ra_pinfo - BOOLEAN Learn Prefix Information in Router Advertisement.
Functional default: enabled if accept_ra is enabled. disabled if accept_ra is disabled.
accept_ra_rt_info_max_plen - INTEGER Maximum prefix length of Route Information in RA.
Route Information w/ prefix larger than or equal to this
variable shall be ignored.
Functional default: 0 if accept_ra_rtr_pref is enabled.
-1 if accept_ra_rtr_pref is disabled.
accept_ra_rtr_pref - BOOLEAN Accept Router Preference in RA.
Functional default: enabled if accept_ra is enabled. disabled if accept_ra is disabled.
accept_redirects - BOOLEAN Accept Redirects.
Functional default: enabled if local forwarding is disabled. disabled if local forwarding is enabled.
accept_source_route - INTEGER Accept source routing (routing extension header).
>= 0: Accept only routing header type 2.
< 0: Do not accept routing header.
Default: 0
autoconf - BOOLEAN Autoconfigure addresses using Prefix Information in Router Advertisements.
Functional default: enabled if accept_ra_pinfo is enabled. disabled if accept_ra_pinfo is disabled.
dad_transmits - INTEGER The amount of Duplicate Address Detection probes to send.
Default: 1
forwarding - BOOLEAN Configure interface-specific Host/Router behaviour.
Note: It is recommended to have the same setting on all
interfaces; mixed router/host scenarios are rather uncommon.
FALSE:
By default, Host behaviour is assumed. This means:
1. IsRouter flag is not set in Neighbour Advertisements.
2. Router Solicitations are being sent when necessary.
3. If accept_ra is TRUE (default), accept Router Advertisements (and do autoconfiguration).
4. If accept_redirects is TRUE (default), accept Redirects.
TRUE:
If local forwarding is enabled, Router behaviour is assumed.
This means exactly the reverse from the above:
1. IsRouter flag is set in Neighbour Advertisements.
2. Router Solicitations are not sent.
3. Router Advertisements are ignored.
4. Redirects are ignored.
Default: FALSE if global forwarding is disabled (default), otherwise TRUE.
hop_limit - INTEGER Default Hop Limit to set.
Default: 64
mtu - INTEGER Default Maximum Transfer Unit
Default: 1280 (IPv6 required minimum)
router_probe_interval - INTEGER Minimum interval (in seconds) between Router Probing described
in RFC4191.
Default: 60
router_solicitation_delay - INTEGER Number of seconds to wait after interface is brought up
before sending Router Solicitations.
Default: 1
router_solicitation_interval - INTEGER Number of seconds to wait between Router Solicitations.
Default: 4
router_solicitations - INTEGER Number of Router Solicitations to send until assuming no
routers are present.
Default: 3
use_tempaddr - INTEGER Preference for Privacy Extensions (RFC3041). <= 0 : disable Privacy Extensions
== 1 : enable Privacy Extensions, but prefer public addresses over temporary addresses. > 1 : enable Privacy Extensions and prefer temporary addresses over public addresses. Default: 0 (for most devices)
-1 (for point-to-point devices and loopback devices)
temp_valid_lft - INTEGER valid lifetime (in seconds) for temporary addresses.
Default: 604800 (7 days)
temp_prefered_lft - INTEGER Preferred lifetime (in seconds) for temporary addresses.
Default: 86400 (1 day)
max_desync_factor - INTEGER Maximum value for DESYNC_FACTOR, which is a random value
that ensures that clients don't synchronize with each
other and generate new addresses at exactly the same time.
value is in seconds.
Default: 600
regen_max_retry - INTEGER Number of attempts before give up attempting to generate
valid temporary addresses.
Default: 5
max_addresses - INTEGER Number of maximum addresses per interface. 0 disables limitation.
It is recommended not set too large value (or 0) because it would
be too easy way to crash kernel to allow to create too much of autoconfigured addresses.
Default: 16
disable_ipv6 - BOOLEAN Disable IPv6 operation. If accept_dad is set to 2, this value
will be dynamically set to TRUE if DAD fails for the link-local
address.
Default: FALSE (enable IPv6 operation)
When this value is changed from 1 to 0 (IPv6 is being enabled),
it will dynamically create a link-local address on the given
interface and start Duplicate Address Detection, if necessary.
When this value is changed from 0 to 1 (IPv6 is being disabled),
it will dynamically delete all address on the given interface.
accept_dad - INTEGER Whether to accept DAD (Duplicate Address Detection). 0: Disable DAD 1: Enable DAD (default) 2: Enable DAD, and disable IPv6 operation if MAC-based duplicate link-local address has been found.
icmp/*: ratelimit - INTEGER Limit the maximal rates for sending ICMPv6 packets. 0 to disable any limiting,
otherwise the minimal space between responses in milliseconds.
Default: 1000
IPv6 Update by: Pekka Savola <pekkas@netcore.fi> YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org>
/proc/sys/net/bridge/* Variables:
bridge-nf-call-arptables - BOOLEAN 1 : pass bridged ARP traffic to arptables' FORWARD chain. 0 : disable this.
Default: 1
bridge-nf-call-iptables - BOOLEAN 1 : pass bridged IPv4 traffic to iptables' chains. 0 : disable this.
Default: 1
bridge-nf-call-ip6tables - BOOLEAN 1 : pass bridged IPv6 traffic to ip6tables' chains. 0 : disable this.
Default: 1
bridge-nf-filter-vlan-tagged - BOOLEAN 1 : pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables. 0 : disable this.
Default: 1
bridge-nf-filter-pppoe-tagged - BOOLEAN 1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables. 0 : disable this.
Default: 1
proc/sys/net/sctp/* Variables:
addip_enable - BOOLEAN Enable or disable extension of Dynamic Address Reconfiguration
(ADD-IP) functionality specified in RFC5061. This extension provides the ability to dynamically add and remove new addresses for the SCTP associations.
1: Enable extension.
0: Disable extension.
Default: 0
addip_noauth_enable - BOOLEAN Dynamic Address Reconfiguration (ADD-IP) requires the use of authentication to protect the operations of adding or removing new addresses. This requirement is mandated so that unauthorized hosts would not be able to hijack associations. However, older implementations may not have implemented this requirement while
allowing the ADD-IP extension. For reasons of interoperability,
we provide this variable to control the enforcement of the authentication requirement.
1: Allow ADD-IP extension to be used without authentication. This should only be set in a closed environment for interoperability
with older implementations.
0: Enforce the authentication requirement
Default: 0
auth_enable - BOOLEAN Enable or disable Authenticated Chunks extension. This extension provides the ability to send and receive authenticated chunks and is required for secure operation of Dynamic Address Reconfiguration
(ADD-IP) extension.
1: Enable this extension. 0: Disable this extension.
Default: 0
prsctp_enable - BOOLEAN Enable or disable the Partial Reliability extension (RFC3758) which
is used to notify peers that a given DATA should no longer be expected.
1: Enable extension 0: Disable
Default: 1
max_burst - INTEGER The limit of the number of new packets that can be initially sent. It controls how bursty the generated traffic can be.
Default: 4
association_max_retrans - INTEGER Set the maximum number for retransmissions that an association can attempt deciding that the remote end is unreachable. If this value
is exceeded, the association is terminated.
Default: 10
max_init_retransmits - INTEGER The maximum number of retransmissions of INIT and COOKIE-ECHO chunks that an association will attempt before declaring the destination unreachable and terminating.
Default: 8
path_max_retrans - INTEGER The maximum number of retransmissions that will be attempted on a given path. Once this threshold is exceeded, the path is considered unreachable, and new traffic will use a different path when the association is multihomed.
Default: 5
rto_initial - INTEGER The initial round trip timeout value in milliseconds that will be used in calculating round trip times. This is the initial time interval
for retransmissions.
Default: 3000
rto_max - INTEGER The maximum value (in milliseconds) of the round trip timeout. This
is the largest time interval that can elapse between retransmissions.
Default: 60000
rto_min - INTEGER The minimum value (in milliseconds) of the round trip timeout. This
is the smallest time interval the can elapse between retransmissions.
Default: 1000
hb_interval - INTEGER The interval (in milliseconds) between HEARTBEAT chunks. These chunks are sent at the specified interval on idle paths to probe the state of
a given path between 2 associations.
Default: 30000
sack_timeout - INTEGER The amount of time (in milliseconds) that the implementation will wait to send a SACK.
Default: 200
valid_cookie_life - INTEGER The default lifetime of the SCTP cookie (in milliseconds). The cookie is used during association establishment.
Default: 60000
cookie_preserve_enable - BOOLEAN Enable or disable the ability to extend the lifetime of the SCTP cookie that is used during the establishment phase of SCTP association
1: Enable cookie lifetime extension. 0: Disable
Default: 1
rcvbuf_policy - INTEGER Determines if the receive buffer is attributed to the socket or to association. SCTP supports the capability to create multiple associations on a single socket. When using this capability, it is possible that a single stalled association that's buffering a lot
of data may block other associations from delivering their data by consuming all of the receive buffer space. To work around this,
the rcvbuf_policy could be set to attribute the receiver buffer space to each association instead of the socket. This prevents the described blocking.
1: rcvbuf space is per association 0: recbuf space is per socket
Default: 0
sndbuf_policy - INTEGER Similar to rcvbuf_policy above, this applies to send buffer space.
1: Send buffer is tracked per association 0: Send buffer is tracked per socket.
Default: 0
sctp_mem - vector of 3 INTEGERs: min, pressure, max Number of pages allowed for queueing by all SCTP sockets.
min: Below this number of pages SCTP is not bothered about its
memory appetite. When amount of memory allocated by SCTP exceeds
this number, SCTP starts to moderate memory usage.
pressure: This value was introduced to follow format of tcp_mem.
max: Number of pages allowed for queueing by all SCTP sockets.
Default is calculated at boot time from amount of available memory.
sctp_rmem - vector of 3 INTEGERs: min, default, max See tcp_rmem for a description.
sctp_wmem - vector of 3 INTEGERs: min, default, max See tcp_wmem for a description.
addr_scope_policy - INTEGER Control IPv4 address scoping - draft-stewart-tsvwg-sctp-ipv4-00
0 - Disable IPv4 address scoping 1 - Enable IPv4 address scoping 2 - Follow draft but allow IPv4 private addresses 3 - Follow draft but allow IPv4 link local addresses
Default: 1
/proc/sys/net/core/* dev_weight - INTEGER The maximum number of packets that kernel can handle on a NAPI
interrupt, it's a Per-CPU variable.
Default: 64
/proc/sys/net/unix/* max_dgram_qlen - INTEGER The maximum length of dgram socket receive queue
Default: 10
UNDOCUMENTED:
/proc/sys/net/irda/* fast_poll_increase FIXME
warn_noreply_time FIXME
discovery_slots FIXME
slot_timeout FIXME
max_baud_rate FIXME
discovery_timeout FIXME
lap_keepalive_time FIXME
max_noreply_time FIXME
max_tx_data_size FIXME
max_tx_window FIXME
min_tx_turn_time FIXME
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