/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 value of TTL field (Time To Live) for outgoing (but not
forwarded) IP packets. Should be between 1 and 255 inclusive.
Default: 64 (as recommended by RFC1700)
ip_no_pmtu_disc - INTEGER
Disable Path MTU Discovery. If enabled in mode 1 and a
fragmentation-required ICMP is received, the PMTU to this
destination will be set to min_pmtu (see below). You will need
to raise min_pmtu to the smallest interface MTU on your system
manually if you want to avoid locally generated fragments.
In mode 2 incoming Path MTU Discovery messages will be
discarded. Outgoing frames are handled the same as in mode 1,
implicitly setting IP_PMTUDISC_DONT on every created socket.
Mode 3 is a hardened pmtu discover mode. The kernel will only
accept fragmentation-needed errors if the underlying protocol
can verify them besides a plain socket lookup. Current
protocols for which pmtu events will be honored are TCP, SCTP
and DCCP as they verify e.g. the sequence number or the
association. This mode should not be enabled globally but is
only intended to secure e.g. name servers in namespaces where
TCP path mtu must still work but path MTU information of other
protocols should be discarded. If enabled globally this mode
could break other protocols.
Possible values: 0-3
Default: FALSE
min_pmtu - INTEGER
default 552 - minimum discovered Path MTU
ip_forward_use_pmtu - BOOLEAN
By default we don't trust protocol path MTUs while forwarding
because they could be easily forged and can lead to unwanted
fragmentation by the router.
You only need to enable this if you have user-space software
which tries to discover path mtus by itself and depends on the
kernel honoring this information. This is normally not the
case.
Default: 0 (disabled)
Possible values:
0 - disabled
1 - enabled
fwmark_reflect - BOOLEAN
Controls the fwmark of kernel-generated IPv4 reply packets that are not
associated with a socket for example, TCP RSTs or ICMP echo replies).
If unset, these packets have a fwmark of zero. If set, they have the
fwmark of the packet they are replying to.
Default: 0
fib_multipath_use_neigh - BOOLEAN
Use status of existing neighbor entry when determining nexthop for
multipath routes. If disabled, neighbor information is not used and
packets could be directed to a failed nexthop. Only valid for kernels
built with CONFIG_IP_ROUTE_MULTIPATH enabled.
Default: 0 (disabled)
Possible values:
0 - disabled
1 - enabled
fib_multipath_hash_policy - INTEGER
Controls which hash policy to use for multipath routes. Only valid
for kernels built with CONFIG_IP_ROUTE_MULTIPATH enabled.
Default: 0 (Layer 3)
Possible values:
0 - Layer 3
1 - Layer 4
2 - Layer 3 or inner Layer 3 if present
fib_sync_mem - UNSIGNED INTEGER
Amount of dirty memory from fib entries that can be backlogged before
synchronize_rcu is forced.
Default: 512kB Minimum: 64kB Maximum: 64MB
ip_forward_update_priority - INTEGER
Whether to update SKB priority from "TOS" field in IPv4 header after it
is forwarded. The new SKB priority is mapped from TOS field value
according to an rt_tos2priority table (see e.g. man tc-prio).
Default: 1 (Update priority.)
Possible values:
0 - Do not update priority.
1 - Update priority.
route/max_size - INTEGER
Maximum number of routes allowed in the kernel. Increase
this when using large numbers of interfaces and/or routes.
From linux kernel 3.6 onwards, this is deprecated for ipv4
as route cache is no longer used.
neigh/default/gc_thresh1 - INTEGER
Minimum number of entries to keep. Garbage collector will not
purge entries if there are fewer than this number.
Default: 128
neigh/default/gc_thresh2 - INTEGER
Threshold when garbage collector becomes more aggressive about
purging entries. Entries older than 5 seconds will be cleared
when over this number.
Default: 512
neigh/default/gc_thresh3 - INTEGER
Maximum number of non-PERMANENT neighbor entries allowed. Increase
this when using large numbers of interfaces and when communicating
with large numbers of directly-connected peers.
Default: 1024
neigh/default/unres_qlen_bytes - INTEGER
The maximum number of bytes which may be used by packets
queued for each unresolved address by other network layers.
(added in linux 3.3)
Setting negative value is meaningless and will return error.
Default: SK_WMEM_MAX, (same as net.core.wmem_default).
Exact value depends on architecture and kernel options,
but should be enough to allow queuing 256 packets
of medium size.
neigh/default/unres_qlen - INTEGER
The maximum number of packets which may be queued for each
unresolved address by other network layers.
(deprecated in linux 3.3) : use unres_qlen_bytes instead.
Prior to linux 3.3, the default value is 3 which may cause
unexpected packet loss. The current default value is calculated
according to default value of unres_qlen_bytes and true size of
packet.
Default: 101
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.
IP Fragmentation:
ipfrag_high_thresh - LONG INTEGER
Maximum memory used to reassemble IP fragments.
ipfrag_low_thresh - LONG INTEGER
(Obsolete since linux-4.17)
Maximum memory used to reassemble IP fragments before the kernel
begins to remove incomplete fragment queues to free up resources.
The kernel still accepts new fragments for defragmentation.
ipfrag_time - INTEGER
Time in seconds to keep an IP fragment in memory.
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.
TCP variables:
somaxconn - INTEGER
Limit of socket listen() backlog, known in userspace as SOMAXCONN.
Defaults to 4096. (Was 128 before linux-5.4)
See also tcp_max_syn_backlog for additional tuning for TCP sockets.
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 sk_pacing_rate is set by TCP stack using a ratio applied
to current rate. (current_rate = cwnd * mss / srtt)
If TCP is in slow start, tcp_pacing_ss_ratio is applied
to let TCP probe for bigger speeds, assuming cwnd can be
doubled every other RTT.
Default: 200
tcp_pacing_ca_ratio - INTEGER
sk->sk_pacing_rate is set by TCP stack using a ratio applied
to current rate. (current_rate = cwnd * mss / srtt)
If TCP is in congestion avoidance phase, tcp_pacing_ca_ratio
is applied to conservatively probe for bigger throughput.
Default: 120
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_reuse - INTEGER
Enable reuse of TIME-WAIT sockets for new connections when it is
safe from protocol viewpoint.
0 - disable
1 - global enable
2 - enable for loopback traffic only
It should not be changed without advice/request of technical
experts.
Default: 2
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_notsent_lowat - UNSIGNED INTEGER
A TCP socket can control the amount of unsent bytes in its write queue,
thanks to TCP_NOTSENT_LOWAT socket option. poll()/select()/epoll()
reports POLLOUT events if the amount of unsent bytes is below a per
socket value, and if the write queue is not full. sendmsg() will
also not add new buffers if the limit is hit.
This global variable controls the amount of unsent data for
sockets not using TCP_NOTSENT_LOWAT. For these sockets, a change
to the global variable has immediate effect.
Default: UINT_MAX (0xFFFFFFFF)
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_thin_linear_timeouts - BOOLEAN
Enable dynamic triggering of linear timeouts for thin streams.
If set, a check is performed upon retransmission by timeout to
determine if the stream is thin (less than 4 packets in flight).
As long as the stream is found to be thin, up to 6 linear
timeouts may be performed before exponential backoff mode is
initiated. This improves retransmission latency for
non-aggressive thin streams, often found to be time-dependent.
For more information on thin streams, see
Documentation/networking/tcp-thin.txt
Default: 0
tcp_limit_output_bytes - INTEGER
Controls TCP Small Queue limit per tcp socket.
TCP bulk sender tends to increase packets in flight until it
gets losses notifications. With SNDBUF autotuning, this can
result in a large amount of packets queued on the local machine
(e.g.: qdiscs, CPU backlog, or device) hurting latency of other
flows, for typical pfifo_fast qdiscs. tcp_limit_output_bytes
limits the number of bytes on qdisc or device to reduce artificial
RTT/cwnd and reduce bufferbloat.
Default: 1048576 (16 * 65536)
tcp_challenge_ack_limit - INTEGER
Limits number of Challenge ACK sent per second, as recommended
in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks)
Default: 1000
tcp_rx_skb_cache - BOOLEAN
Controls a per TCP socket cache of one skb, that might help
performance of some workloads. This might be dangerous
on systems with a lot of TCP sockets, since it increases
memory usage.
Default: 0 (disabled)
UDP variables:
udp_l3mdev_accept - BOOLEAN
Enabling this option allows a "global" bound socket to work
across L3 master domains (e.g., VRFs) with packets capable of
being received regardless of the L3 domain in which they
originated. Only valid when the kernel was compiled with
CONFIG_NET_L3_MASTER_DEV.
Default: 0 (disabled)
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: 4K
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: 4K
RAW variables:
raw_l3mdev_accept - BOOLEAN
Enabling this option allows a "global" bound socket to work
across L3 master domains (e.g., VRFs) with packets capable of
being received regardless of the L3 domain in which they
originated. Only valid when the kernel was compiled with
CONFIG_NET_L3_MASTER_DEV.
Default: 1 (enabled)
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.
If possible, it is better these numbers have different parity
(one even and one odd value).
Must be greater than or equal to ip_unprivileged_port_start.
The default values are 32768 and 60999 respectively.
ip_local_reserved_ports - list of comma separated ranges
Specify the ports which are reserved for known third-party
applications. These ports will not be used by automatic port
assignments (e.g. when calling connect() or bind() with port
number 0). Explicit port allocation behavior is unchanged.
The format used for both input and output is a comma separated
list of ranges (e.g. "1,2-4,10-10" for ports 1, 2, 3, 4 and
10). Writing to the file will clear all previously reserved
ports and update the current list with the one given in the
input.
Note that ip_local_port_range and ip_local_reserved_ports
settings are independent and both are considered by the kernel
when determining which ports are available for automatic port
assignments.
You can reserve ports which are not in the current
ip_local_port_range, e.g.:
$ cat /proc/sys/net/ipv4/ip_local_port_range
32000 60999
$ cat /proc/sys/net/ipv4/ip_local_reserved_ports
8080,9148
although this is redundant. However such a setting is useful
if later the port range is changed to a value that will
include the reserved ports.
Default: Empty
ip_unprivileged_port_start - INTEGER
This is a per-namespace sysctl. It defines the first
unprivileged port in the network namespace. Privileged ports
require root or CAP_NET_BIND_SERVICE in order to bind to them.
To disable all privileged ports, set this to 0. They must not
overlap with the ip_local_port_range.
Default: 1024
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_autobind_reuse - BOOLEAN
By default, bind() does not select the ports automatically even if
the new socket and all sockets bound to the port have SO_REUSEADDR.
ip_autobind_reuse allows bind() to reuse the port and this is useful
when you use bind()+connect(), but may break some applications.
The preferred solution is to use IP_BIND_ADDRESS_NO_PORT and this
option should only be set by experts.
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
ip_early_demux - BOOLEAN
Optimize input packet processing down to one demux for
certain kinds of local sockets. Currently we only do this
for established TCP and connected UDP sockets.
It may add an additional cost for pure routing workloads that
reduces overall throughput, in such case you should disable it.
Default: 1
ping_group_range - 2 INTEGERS
Restrict ICMP_PROTO datagram sockets to users in the group range.
The default is "1 0", meaning, that nobody (not even root) may
create ping sockets. Setting it to "100 100" would grant permissions
to the single group. "0 4294967295" would enable it for the world, "100
4294967295" would enable it for the users, but not daemons.
tcp_early_demux - BOOLEAN
Enable early demux for established TCP sockets.
Default: 1
udp_early_demux - BOOLEAN
Enable early demux for connected UDP sockets. Disable this if
your system could experience more unconnected load.
Default: 1
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.
Note that another sysctl, icmp_msgs_per_sec limits the number
of ICMP packets sent on all targets.
Default: 1000
icmp_msgs_per_sec - INTEGER
Limit maximal number of ICMP packets sent per second from this host.
Only messages whose type matches icmp_ratemask (see below) are
controlled by this limit.
Default: 1000
icmp_msgs_burst - INTEGER
icmp_msgs_per_sec controls number of ICMP packets sent per second,
while icmp_msgs_burst controls the burst size of these packets.
Default: 50
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: 1
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
Theoretical maximum value is bounded by having to send a membership
report in a single datagram (i.e. the report can't span multiple
datagrams, or risk confusing the switch and leaving groups you don't
intend to).
The number of supported groups 'M' is bounded by the number of group
report entries you can fit into a single datagram of 65535 bytes.
M = 65536-sizeof (ip header)/(sizeof(Group record))
Group records are variable length, with a minimum of 12 bytes.
So net.ipv4.igmp_max_memberships should not be set higher than:
(65536-24) / 12 = 5459
The value 5459 assumes no IP header options, so in practice
this number may be lower.
igmp_max_msf - INTEGER
Maximum number of addresses allowed in the source filter list for a
multicast group.
Default: 10
igmp_qrv - INTEGER
Controls the IGMP query robustness variable (see RFC2236 8.1).
Default: 2 (as specified by RFC2236 8.1)
Minimum: 1 (as specified by RFC6636 4.5)
force_igmp_version - INTEGER
0 - (default) No enforcement of a IGMP version, IGMPv1/v2 fallback
allowed. Will back to IGMPv3 mode again if all IGMPv1/v2 Querier
Present timer expires.
1 - Enforce to use IGMP version 1. Will also reply IGMPv1 report if
receive IGMPv2/v3 query.
2 - Enforce to use IGMP version 2. Will fallback to IGMPv1 if receive
IGMPv1 query message. Will reply report if receive IGMPv3 query.
3 - Enforce to use IGMP version 3. The same react with default 0.
Note: this is not the same with force_mld_version because IGMPv3 RFC3376
Security Considerations does not have clear description that we could
ignore other version messages completely as MLDv2 RFC3810. So make
this value as default 0 is recommended.
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. This controls whether packets
received _on_ this interface can be forwarded.
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
proxy_arp_pvlan - BOOLEAN
Private VLAN proxy arp.
Basically allow proxy arp replies back to the same interface
(from which the ARP request/solicitation was received).
This is done to support (ethernet) switch features, like RFC
3069, where the individual ports are NOT allowed to
communicate with each other, but they are allowed to talk to
the upstream router. As described in RFC 3069, it is possible
to allow these hosts to communicate through the upstream
router by proxy_arp'ing. Don't need to be used together with
proxy_arp.
This technology is known by different names:
In RFC 3069 it is called VLAN Aggregation.
Cisco and Allied Telesyn call it Private VLAN.
Hewlett-Packard call it Source-Port filtering or port-isolation.
Ericsson call it MAC-Forced Forwarding (RFC Draft).
shared_media - BOOLEAN
Send(router) or accept(host) RFC1620 shared media redirects.
Overrides 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 to gateways listed in the
interface's current gateway list. Even if disabled, RFC1122 redirect
rules still apply.
Overridden by shared_media.
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)
accept_local - BOOLEAN
Accept packets with local source addresses. In combination with
suitable routing, this can be used to direct packets between two
local interfaces over the wire and have them accepted properly.
default FALSE
route_localnet - BOOLEAN
Do not consider loopback addresses as martian source or destination
while routing. This enables the use of 127/8 for local routing purposes.
default FALSE
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.
The max value from conf/{all,interface}/rp_filter is used
when doing 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 requests when device is brought up
or hardware address changes.
arp_accept - BOOLEAN
Define behavior for gratuitous ARP frames who's IP is not
already present in the ARP table:
0 - don't create new entries in the ARP table
1 - create new entries in the ARP table
Both replies and requests type gratuitous arp will trigger the
ARP table to be updated, if this setting is on.
If the ARP table already contains the IP address of the
gratuitous arp frame, the arp table will be updated regardless
if this setting is on or off.
mcast_solicit - INTEGER
The maximum number of multicast probes in INCOMPLETE state,
when the associated hardware address is unknown. Defaults
to 3.
ucast_solicit - INTEGER
The maximum number of unicast probes in PROBE state, when
the hardware address is being reconfirmed. Defaults to 3.
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_resolicit). Defaults to 0.
mcast_resolicit - INTEGER
The maximum number of multicast probes after unicast and
app probes in PROBE state. 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
igmpv2_unsolicited_report_interval - INTEGER
The interval in milliseconds in which the next unsolicited
IGMPv1 or IGMPv2 report retransmit will take place.
Default: 10000 (10 seconds)
igmpv3_unsolicited_report_interval - INTEGER
The interval in milliseconds in which the next unsolicited
IGMPv3 report retransmit will take place.
Default: 1000 (1 seconds)
promote_secondaries - BOOLEAN
When a primary IP address is removed from this interface
promote a corresponding secondary IP address instead of
removing all the corresponding secondary IP addresses.
drop_unicast_in_l2_multicast - BOOLEAN
Drop any unicast IP packets that are received in link-layer
multicast (or broadcast) frames.
This behavior (for multicast) is actually a SHOULD in RFC
1122, but is disabled by default for compatibility reasons.
Default: off (0)
drop_gratuitous_arp - BOOLEAN
Drop all gratuitous ARP frames, for example if there's a known
good ARP proxy on the network and such frames need not be used
(or in the case of 802.11, must not be used to prevent attacks.)
Default: off (0)
tag - INTEGER
Allows you to write a number, which can be used as required.
Default value is 0.
xfrm4_gc_thresh - INTEGER
(Obsolete since linux-4.14)
The threshold at which we will start garbage collecting for IPv4
destination cache entries. At twice this value the system will
refuse new allocations.
igmp_link_local_mcast_reports - BOOLEAN
Enable IGMP reports for link local multicast groups in the
224.0.0.X range.
Default TRUE
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 RFC3493)
flowlabel_consistency - BOOLEAN
Protect the consistency (and unicity) of flow label.
You have to disable it to use IPV6_FL_F_REFLECT flag on the
flow label manager.
TRUE: enabled
FALSE: disabled
Default: TRUE
auto_flowlabels - INTEGER
Automatically generate flow labels based on a flow hash of the
packet. This allows intermediate devices, such as routers, to
identify packet flows for mechanisms like Equal Cost Multipath
Routing (see RFC 6438).
0: automatic flow labels are completely disabled
1: automatic flow labels are enabled by default, they can be
disabled on a per socket basis using the IPV6_AUTOFLOWLABEL
socket option
2: automatic flow labels are allowed, they may be enabled on a
per socket basis using the IPV6_AUTOFLOWLABEL socket option
3: automatic flow labels are enabled and enforced, they cannot
be disabled by the socket option
Default: 1
flowlabel_state_ranges - BOOLEAN
Split the flow label number space into two ranges. 0-0x7FFFF is
reserved for the IPv6 flow manager facility, 0x80000-0xFFFFF
is reserved for stateless flow labels as described in RFC6437.
TRUE: enabled
FALSE: disabled
Default: true
flowlabel_reflect - INTEGER
Control flow label reflection. Needed for Path MTU
Discovery to work with Equal Cost Multipath Routing in anycast
environments. See RFC 7690 and:
https://tools.ietf.org/html/draft-wang-6man-flow-label-reflection-01
This is a bitmask.
1: enabled for established flows
Note that this prevents automatic flowlabel changes, as done
in "tcp: change IPv6 flow-label upon receiving spurious retransmission"
and "tcp: Change txhash on every SYN and RTO retransmit"
2: enabled for TCP RESET packets (no active listener)
If set, a RST packet sent in response to a SYN packet on a closed
port will reflect the incoming flow label.
4: enabled for ICMPv6 echo reply messages.
Default: 0
fib_multipath_hash_policy - INTEGER
Controls which hash policy to use for multipath routes.
Default: 0 (Layer 3)
Possible values:
0 - Layer 3 (source and destination addresses plus flow label)
1 - Layer 4 (standard 5-tuple)
2 - Layer 3 or inner Layer 3 if present
anycast_src_echo_reply - BOOLEAN
Controls the use of anycast addresses as source addresses for ICMPv6
echo reply
TRUE: enabled
FALSE: disabled
Default: FALSE
idgen_delay - INTEGER
Controls the delay in seconds after which time to retry
privacy stable address generation if a DAD conflict is
detected.
Default: 1 (as specified in RFC7217)
idgen_retries - INTEGER
Controls the number of retries to generate a stable privacy
address if a DAD conflict is detected.
Default: 3 (as specified in RFC7217)
mld_qrv - INTEGER
Controls the MLD query robustness variable (see RFC3810 9.1).
Default: 2 (as specified by RFC3810 9.1)
Minimum: 1 (as specified by RFC6636 4.5)
max_dst_opts_number - INTEGER
Maximum number of non-padding TLVs allowed in a Destination
options extension header. If this value is less than zero
then unknown options are disallowed and the number of known
TLVs allowed is the absolute value of this number.
Default: 8
max_hbh_opts_number - INTEGER
Maximum number of non-padding TLVs allowed in a Hop-by-Hop
options extension header. If this value is less than zero
then unknown options are disallowed and the number of known
TLVs allowed is the absolute value of this number.
Default: 8
max_dst_opts_length - INTEGER
Maximum length allowed for a Destination options extension
header.
Default: INT_MAX (unlimited)
max_hbh_length - INTEGER
Maximum length allowed for a Hop-by-Hop options extension
header.
Default: INT_MAX (unlimited)
skip_notify_on_dev_down - BOOLEAN
Controls whether an RTM_DELROUTE message is generated for routes
removed when a device is taken down or deleted. IPv4 does not
generate this message; IPv6 does by default. Setting this sysctl
to true skips the message, making IPv4 and IPv6 on par in relying
on userspace caches to track link events and evict routes.
Default: false (generate message)
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.
IPv6 Segment Routing:
seg6_flowlabel - INTEGER
Controls the behaviour of computing the flowlabel of outer
IPv6 header in case of SR T.encaps
-1 set flowlabel to zero.
0 copy flowlabel from Inner packet in case of Inner IPv6
(Set flowlabel to 0 in case IPv4/L2)
1 Compute the flowlabel using seg6_make_flowlabel()
Default is 0.
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.
fwmark_reflect - BOOLEAN
Controls the fwmark of kernel-generated IPv6 reply packets that are not
associated with a socket for example, TCP RSTs or ICMPv6 echo replies).
If unset, these packets have a fwmark of zero. If set, they have the
fwmark of the packet they are replying to.
Default: 0
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 - INTEGER
Accept Router Advertisements; autoconfigure using them.
It also determines whether or not to transmit Router
Solicitations. If and only if the functional setting is to
accept Router Advertisements, Router Solicitations will be
transmitted.
Possible values are:
0 Do not accept Router Advertisements.
1 Accept Router Advertisements if forwarding is disabled.
2 Overrule forwarding behaviour. Accept Router Advertisements
even if forwarding is enabled.
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_from_local - BOOLEAN
Accept RA with source-address that is found on local machine
if the RA is otherwise proper and able to be accepted.
Default is to NOT accept these as it may be an un-intended
network loop.
Functional default:
enabled if accept_ra_from_local is enabled
on a specific interface.
disabled if accept_ra_from_local is disabled
on a specific interface.
accept_ra_min_hop_limit - INTEGER
Minimum hop limit Information in Router Advertisement.
Hop limit Information in Router Advertisement less than this
variable shall be ignored.
Default: 1
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_min_plen - INTEGER
Minimum prefix length of Route Information in RA.
Route Information w/ prefix smaller than 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_rt_info_max_plen - INTEGER
Maximum prefix length of Route Information in RA.
Route Information w/ prefix larger than 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_ra_mtu - BOOLEAN
Apply the MTU value specified in RA option 5 (RFC4861). If
disabled, the MTU specified in the RA will be ignored.
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.
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)
keep_addr_on_down - INTEGER
Keep all IPv6 addresses on an interface down event. If set static
global addresses with no expiration time are not flushed.
>0 : enabled
0 : system default
YOSHIFUJI Hideaki / USAGI Project