/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 <= 0. Possible values are [-31, 31], inclusive. Default: 1 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_autocorking - BOOLEAN Enable TCP auto corking : When applications do consecutive small write()/sendmsg() system calls, we try to coalesce these small writes as much as possible, to lower total amount of sent packets. This is done if at least one prior packet for the flow is waiting in Qdisc queues or device transmit queue. Applications can still use TCP_CORK for optimal behavior when they know how/when to uncork their sockets. Default : 1 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_mtu_probe_floor - INTEGER If MTU probing is enabled this caps the minimum MSS used for search_low for the connection. Default : 48 tcp_min_snd_mss - INTEGER TCP SYN and SYNACK messages usually advertise an ADVMSS option, as described in RFC 1122 and RFC 6691. If this ADVMSS option is smaller than tcp_min_snd_mss, it is silently capped to tcp_min_snd_mss. Default : 48 (at least 8 bytes of payload per segment) 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. For passive connections, the listener congestion control choice is inherited. [see setsockopt(listenfd, SOL_TCP, TCP_CONGESTION, "name" ...) ] tcp_dsack - BOOLEAN Allows TCP to send "duplicate" SACKs. tcp_early_retrans - INTEGER Tail loss probe (TLP) converts RTOs occurring due to tail losses into fast recovery (draft-ietf-tcpm-rack). Note that TLP requires RACK to function properly (see tcp_recovery below) Possible values: 0 disables TLP 3 or 4 enables TLP Default: 3 tcp_ecn - INTEGER Control use of Explicit Congestion Notification (ECN) by TCP. ECN is used only when both ends of the TCP connection indicate support for it. This feature is useful in avoiding losses due to congestion by allowing supporting routers to signal congestion before having to drop packets. Possible values are: 0 Disable ECN. Neither initiate nor accept ECN. 1 Enable ECN when requested by incoming connections and also request ECN on outgoing connection attempts. 2 Enable ECN when requested by incoming connections but do not request ECN on outgoing connections. Default: 2 tcp_ecn_fallback - BOOLEAN If the kernel detects that ECN connection misbehaves, enable fall back to non-ECN. Currently, this knob implements the fallback from RFC3168, section 6.1.1.1., but we reserve that in future, additional detection mechanisms could be implemented under this knob. The value is not used, if tcp_ecn or per route (or congestion control) ECN settings are disabled. Default: 1 (fallback enabled) tcp_fack - BOOLEAN This is a legacy option, it has no effect anymore. tcp_fin_timeout - INTEGER The length of time an orphaned (no longer referenced by any application) connection will remain in the FIN_WAIT_2 state before it is aborted at the local end. While a perfectly valid "receive only" state for an un-orphaned connection, an orphaned connection in FIN_WAIT_2 state could otherwise wait forever for the remote to close its end of the connection. Cf. tcp_max_orphans Default: 60 seconds tcp_frto - INTEGER Enables Forward RTO-Recovery (F-RTO) defined in RFC5682. F-RTO is an enhanced recovery algorithm for TCP retransmission timeouts. It is particularly beneficial in networks where the RTT fluctuates (e.g., wireless). F-RTO is sender-side only modification. It does not require any support from the peer. By default it's enabled with a non-zero value. 0 disables F-RTO. tcp_fwmark_accept - BOOLEAN If set, incoming connections to listening sockets that do not have a socket mark will set the mark of the accepting socket to the fwmark of the incoming SYN packet. This will cause all packets on that connection (starting from the first SYNACK) to be sent with that fwmark. The listening socket's mark is unchanged. Listening sockets that already have a fwmark set via setsockopt(SOL_SOCKET, SO_MARK, ...) are unaffected. Default: 0 tcp_invalid_ratelimit - INTEGER Limit the maximal rate for sending duplicate acknowledgments in response to incoming TCP packets that are for an existing connection but that are invalid due to any of these reasons: (a) out-of-window sequence number, (b) out-of-window acknowledgment number, or (c) PAWS (Protection Against Wrapped Sequence numbers) check failure This can help mitigate simple "ack loop" DoS attacks, wherein a buggy or malicious middlebox or man-in-the-middle can rewrite TCP header fields in manner that causes each endpoint to think that the other is sending invalid TCP segments, thus causing each side to send an unterminating stream of duplicate acknowledgments for invalid segments. Using 0 disables rate-limiting of dupacks in response to invalid segments; otherwise this value specifies the minimal space between sending such dupacks, in milliseconds. Default: 500 (milliseconds). 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_l3mdev_accept - BOOLEAN Enables child sockets to inherit the L3 master device index. Enabling this option allows a "global" listen socket to work across L3 master domains (e.g., VRFs) with connected sockets derived from the listen socket to be bound to the L3 domain in which the packets originated. Only valid when the kernel was compiled with CONFIG_NET_L3_MASTER_DEV. Default: 0 (disabled) tcp_low_latency - BOOLEAN This is a legacy option, it has no effect anymore. 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 (SYN_RECV), which have not received an acknowledgment from connecting client. This is a per-listener limit. The minimal value is 128 for low memory machines, and it will increase in proportion to the memory of machine. If server suffers from overload, try increasing this number. Remember to also check /proc/sys/net/core/somaxconn A SYN_RECV request socket consumes about 304 bytes of memory. 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_min_rtt_wlen - INTEGER The window length of the windowed min filter to track the minimum RTT. A shorter window lets a flow more quickly pick up new (higher) minimum RTT when it is moved to a longer path (e.g., due to traffic engineering). A longer window makes the filter more resistant to RTT inflations such as transient congestion. The unit is seconds. Possible values: 0 - 86400 (1 day) Default: 300 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_probe_interval - UNSIGNED INTEGER Controls how often to start TCP Packetization-Layer Path MTU Discovery reprobe. The default is reprobing every 10 minutes as per RFC4821. tcp_probe_threshold - INTEGER Controls when TCP Packetization-Layer Path MTU Discovery probing will stop in respect to the width of search range in bytes. Default is 8 bytes. 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_no_ssthresh_metrics_save - BOOLEAN Controls whether TCP saves ssthresh metrics in the route cache. Default is 1, which disables ssthresh metrics. 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 8. 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_recovery - INTEGER This value is a bitmap to enable various experimental loss recovery features. RACK: 0x1 enables the RACK loss detection for fast detection of lost retransmissions and tail drops. It also subsumes and disables RFC6675 recovery for SACK connections. RACK: 0x2 makes RACK's reordering window static (min_rtt/4). RACK: 0x4 disables RACK's DUPACK threshold heuristic Default: 0x1 tcp_reordering - INTEGER Initial reordering level of packets in a TCP stream. TCP stack can then dynamically adjust flow reordering level between this initial value and tcp_max_reordering Default: 3 tcp_max_reordering - INTEGER Maximal reordering level of packets in a TCP stream. 300 is a fairly conservative value, but you might increase it if paths are using per packet load balancing (like bonding rr mode) Default: 300 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: 4K 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 6MB, depending on RAM size. tcp_sack - BOOLEAN Enable select acknowledgments (SACKS). tcp_comp_sack_delay_ns - LONG INTEGER TCP tries to reduce number of SACK sent, using a timer based on 5% of SRTT, capped by this sysctl, in nano seconds. The default is 1ms, based on TSO autosizing period. Default : 1,000,000 ns (1 ms) tcp_comp_sack_nr - INTEGER Max number of SACK that can be compressed. Using 0 disables SACK compression. Default : 44 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 31seconds till the last retransmission with the current initial RTO of 1second. With this the final timeout for a passive TCP connection will happen after 63seconds. tcp_syncookies - INTEGER Only valid when the kernel was compiled with CONFIG_SYN_COOKIES Send out syncookies when the syn backlog queue of a socket overflows. This is to prevent against the common 'SYN flood attack' Default: 1 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. If you want to test which effects syncookies have to your network connections you can set this knob to 2 to enable unconditionally generation of syncookies. tcp_fastopen - INTEGER Enable TCP Fast Open (RFC7413) to send and accept data in the opening SYN packet. The client support is enabled by flag 0x1 (on by default). The client then must use sendmsg() or sendto() with the MSG_FASTOPEN flag, rather than connect() to send data in SYN. The server support is enabled by flag 0x2 (off by default). Then either enable for all listeners with another flag (0x400) or enable individual listeners via TCP_FASTOPEN socket option with the option value being the length of the syn-data backlog. The values (bitmap) are 0x1: (client) enables sending data in the opening SYN on the client. 0x2: (server) enables the server support, i.e., allowing data in a SYN packet to be accepted and passed to the application before 3-way handshake finishes. 0x4: (client) send data in the opening SYN regardless of cookie availability and without a cookie option. 0x200: (server) accept data-in-SYN w/o any cookie option present. 0x400: (server) enable all listeners to support Fast Open by default without explicit TCP_FASTOPEN socket option. Default: 0x1 Note that that additional client or server features are only effective if the basic support (0x1 and 0x2) are enabled respectively. tcp_fastopen_blackhole_timeout_sec - INTEGER Initial time period in second to disable Fastopen on active TCP sockets when a TFO firewall blackhole issue happens. This time period will grow exponentially when more blackhole issues get detected right after Fastopen is re-enabled and will reset to initial value when the blackhole issue goes away. 0 to disable the blackhole detection. By default, it is set to 1hr. tcp_fastopen_key - list of comma separated 32-digit hexadecimal INTEGERs The list consists of a primary key and an optional backup key. The primary key is used for both creating and validating cookies, while the optional backup key is only used for validating cookies. The purpose of the backup key is to maximize TFO validation when keys are rotated. A randomly chosen primary key may be configured by the kernel if the tcp_fastopen sysctl is set to 0x400 (see above), or if the TCP_FASTOPEN setsockopt() optname is set and a key has not been previously configured via sysctl. If keys are configured via setsockopt() by using the TCP_FASTOPEN_KEY optname, then those per-socket keys will be used instead of any keys that are specified via sysctl. A key is specified as 4 8-digit hexadecimal integers which are separated by a '-' as: xxxxxxxx-xxxxxxxx-xxxxxxxx-xxxxxxxx. Leading zeros may be omitted. A primary and a backup key may be specified by separating them by a comma. If only one key is specified, it becomes the primary key and any previously configured backup keys are removed. tcp_syn_retries - INTEGER Number of times initial SYNs for an active TCP connection attempt will be retransmitted. Should not be higher than 127. Default value is 6, which corresponds to 63seconds till the last retransmission with the current initial RTO of 1second. With this the final timeout for an active TCP connection attempt will happen after 127seconds. tcp_timestamps - INTEGER Enable timestamps as defined in RFC1323. 0: Disabled. 1: Enable timestamps as defined in RFC1323 and use random offset for each connection rather than only using the current time. 2: Like 1, but without random offsets. Default: 1 tcp_min_tso_segs - INTEGER Minimal number of segments per TSO frame. Since linux-3.12, TCP does an automatic sizing of TSO frames, depending on flow rate, instead of filling 64Kbytes packets. For specific usages, it's possible to force TCP to build big TSO frames. Note that TCP stack might split too big TSO packets if available window is too small. Default: 2 tcp_pacing_ss_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 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. < 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 - INTEGER 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. Possible values are: 0 Forwarding disabled 1 Forwarding enabled FALSE (0): By default, Host behaviour is assumed. This means: 1. IsRouter flag is not set in Neighbour Advertisements. 2. If accept_ra is TRUE (default), transmit Router Solicitations. 3. If accept_ra is TRUE (default), accept Router Advertisements (and do autoconfiguration). 4. If accept_redirects is TRUE (default), accept Redirects. TRUE (1): 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 unless accept_ra is 2. 3. Router Advertisements are ignored unless accept_ra is 2. 4. Redirects are ignored. Default: 0 (disabled) if global forwarding is disabled (default), otherwise 1 (enabled). hop_limit - INTEGER Default Hop Limit to set. Default: 64 mtu - INTEGER Default Maximum Transfer Unit Default: 1280 (IPv6 required minimum) ip_nonlocal_bind - BOOLEAN If set, allows processes to bind() to non-local IPv6 addresses, which can be quite useful - but may break some applications. Default: 0 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_oif_addrs_only - BOOLEAN When enabled, the candidate source addresses for destinations routed via this interface are restricted to the set of addresses configured on this interface (vis. RFC 6724, section 4). Default: false 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) 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 <0 : disabled Default: 0 (addresses are removed) 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 Maximum number of autoconfigured addresses per interface. Setting to zero disables the limitation. It is not recommended to set this value too large (or to zero) because it would be an easy way to crash the kernel by allowing too many addresses to be created. 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 addresses and routes on the given interface. From now on it will not possible to add addresses/routes to the selected 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. DAD operation and mode on a given interface will be selected according to the maximum value of conf/{all,interface}/accept_dad. force_tllao - BOOLEAN Enable sending the target link-layer address option even when responding to a unicast neighbor solicitation. Default: FALSE Quoting from RFC 2461, section 4.4, Target link-layer address: "The option MUST be included for multicast solicitations in order to avoid infinite Neighbor Solicitation "recursion" when the peer node does not have a cache entry to return a Neighbor Advertisements message. When responding to unicast solicitations, the option can be omitted since the sender of the solicitation has the correct link- layer address; otherwise it would not have be able to send the unicast solicitation in the first place. However, including the link-layer address in this case adds little overhead and eliminates a potential race condition where the sender deletes the cached link-layer address prior to receiving a response to a previous solicitation." ndisc_notify - BOOLEAN Define mode for notification of address and device changes. 0 - (default): do nothing 1 - Generate unsolicited neighbour advertisements when device is brought up or hardware address changes. ndisc_tclass - INTEGER The IPv6 Traffic Class to use by default when sending IPv6 Neighbor Discovery (Router Solicitation, Router Advertisement, Neighbor Solicitation, Neighbor Advertisement, Redirect) messages. These 8 bits can be interpreted as 6 high order bits holding the DSCP value and 2 low order bits representing ECN (which you probably want to leave cleared). 0 - (default) mldv1_unsolicited_report_interval - INTEGER The interval in milliseconds in which the next unsolicited MLDv1 report retransmit will take place. Default: 10000 (10 seconds) mldv2_unsolicited_report_interval - INTEGER The interval in milliseconds in which the next unsolicited MLDv2 report retransmit will take place. Default: 1000 (1 second) force_mld_version - INTEGER 0 - (default) No enforcement of a MLD version, MLDv1 fallback allowed 1 - Enforce to use MLD version 1 2 - Enforce to use MLD version 2 suppress_frag_ndisc - INTEGER Control RFC 6980 (Security Implications of IPv6 Fragmentation with IPv6 Neighbor Discovery) behavior: 1 - (default) discard fragmented neighbor discovery packets 0 - allow fragmented neighbor discovery packets optimistic_dad - BOOLEAN Whether to perform Optimistic Duplicate Address Detection (RFC 4429). 0: disabled (default) 1: enabled Optimistic Duplicate Address Detection for the interface will be enabled if at least one of conf/{all,interface}/optimistic_dad is set to 1, it will be disabled otherwise. use_optimistic - BOOLEAN If enabled, do not classify optimistic addresses as deprecated during source address selection. Preferred addresses will still be chosen before optimistic addresses, subject to other ranking in the source address selection algorithm. 0: disabled (default) 1: enabled This will be enabled if at least one of conf/{all,interface}/use_optimistic is set to 1, disabled otherwise. stable_secret - IPv6 address This IPv6 address will be used as a secret to generate IPv6 addresses for link-local addresses and autoconfigured ones. All addresses generated after setting this secret will be stable privacy ones by default. This can be changed via the addrgenmode ip-link. conf/default/stable_secret is used as the secret for the namespace, the interface specific ones can overwrite that. Writes to conf/all/stable_secret are refused. It is recommended to generate this secret during installation of a system and keep it stable after that. By default the stable secret is unset. addr_gen_mode - INTEGER Defines how link-local and autoconf addresses are generated. 0: generate address based on EUI64 (default) 1: do no generate a link-local address, use EUI64 for addresses generated from autoconf 2: generate stable privacy addresses, using the secret from stable_secret (RFC7217) 3: generate stable privacy addresses, using a random secret if unset drop_unicast_in_l2_multicast - BOOLEAN Drop any unicast IPv6 packets that are received in link-layer multicast (or broadcast) frames. By default this is turned off. drop_unsolicited_na - BOOLEAN Drop all unsolicited neighbor advertisements, for example if there's a known good NA 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.) By default this is turned off. enhanced_dad - BOOLEAN Include a nonce option in the IPv6 neighbor solicitation messages used for duplicate address detection per RFC7527. A received DAD NS will only signal a duplicate address if the nonce is different. This avoids any false detection of duplicates due to loopback of the NS messages that we send. The nonce option will be sent on an interface unless both of conf/{all,interface}/enhanced_dad are set to FALSE. Default: TRUE icmp/*: ratelimit - INTEGER Limit the maximal rates for sending ICMPv6 messages. 0 to disable any limiting, otherwise the minimal space between responses in milliseconds. Default: 1000 ratemask - list of comma separated ranges For ICMPv6 message types matching the ranges in the ratemask, limit the sending of the message according to ratelimit parameter. The format used for both input and output is a comma separated list of ranges (e.g. "0-127,129" for ICMPv6 message type 0 to 127 and 129). Writing to the file will clear all previous ranges of ICMPv6 message types and update the current list with the input. Refer to: https://www.iana.org/assignments/icmpv6-parameters/icmpv6-parameters.xhtml for numerical values of ICMPv6 message types, e.g. echo request is 128 and echo reply is 129. Default: 0-1,3-127 (rate limit ICMPv6 errors except Packet Too Big) echo_ignore_all - BOOLEAN If set non-zero, then the kernel will ignore all ICMP ECHO requests sent to it over the IPv6 protocol. Default: 0 echo_ignore_multicast - BOOLEAN If set non-zero, then the kernel will ignore all ICMP ECHO requests sent to it over the IPv6 protocol via multicast. Default: 0 echo_ignore_anycast - BOOLEAN If set non-zero, then the kernel will ignore all ICMP ECHO requests sent to it over the IPv6 protocol destined to anycast address. Default: 0 xfrm6_gc_thresh - INTEGER (Obsolete since linux-4.14) The threshold at which we will start garbage collecting for IPv6 destination cache entries. At twice this value the system will refuse new allocations. 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: 0 bridge-nf-filter-pppoe-tagged - BOOLEAN 1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables. 0 : disable this. Default: 0 bridge-nf-pass-vlan-input-dev - BOOLEAN 1: if bridge-nf-filter-vlan-tagged is enabled, try to find a vlan interface on the bridge and set the netfilter input device to the vlan. This allows use of e.g. "iptables -i br0.1" and makes the REDIRECT target work with vlan-on-top-of-bridge interfaces. When no matching vlan interface is found, or this switch is off, the input device is set to the bridge interface. 0: disable bridge netfilter vlan interface lookup. Default: 0 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 pf_enable - INTEGER Enable or disable pf (pf is short for potentially failed) state. A value of pf_retrans > path_max_retrans also disables pf state. That is, one of both pf_enable and pf_retrans > path_max_retrans can disable pf state. Since pf_retrans and path_max_retrans can be changed by userspace application, sometimes user expects to disable pf state by the value of pf_retrans > path_max_retrans, but occasionally the value of pf_retrans or path_max_retrans is changed by the user application, this pf state is enabled. As such, it is necessary to add this to dynamically enable and disable pf state. See: https://datatracker.ietf.org/doc/draft-ietf-tsvwg-sctp-failover for details. 1: Enable pf. 0: Disable pf. Default: 1 pf_expose - INTEGER Unset or enable/disable pf (pf is short for potentially failed) state exposure. Applications can control the exposure of the PF path state in the SCTP_PEER_ADDR_CHANGE event and the SCTP_GET_PEER_ADDR_INFO sockopt. When it's unset, no SCTP_PEER_ADDR_CHANGE event with SCTP_ADDR_PF state will be sent and a SCTP_PF-state transport info can be got via SCTP_GET_PEER_ADDR_INFO sockopt; When it's enabled, a SCTP_PEER_ADDR_CHANGE event will be sent for a transport becoming SCTP_PF state and a SCTP_PF-state transport info can be got via SCTP_GET_PEER_ADDR_INFO sockopt; When it's diabled, no SCTP_PEER_ADDR_CHANGE event will be sent and it returns -EACCES when trying to get a SCTP_PF-state transport info via SCTP_GET_PEER_ADDR_INFO sockopt. 0: Unset pf state exposure, Compatible with old applications. 1: Disable pf state exposure. 2: Enable pf state exposure. 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 pf_retrans - INTEGER The number of retransmissions that will be attempted on a given path before traffic is redirected to an alternate transport (should one exist). Note this is distinct from path_max_retrans, as a path that passes the pf_retrans threshold can still be used. Its only deprioritized when a transmission path is selected by the stack. This setting is primarily used to enable fast failover mechanisms without having to reduce path_max_retrans to a very low value. See: http://www.ietf.org/id/draft-nishida-tsvwg-sctp-failover-05.txt for details. Note also that a value of pf_retrans > path_max_retrans disables this feature. Since both pf_retrans and path_max_retrans can be changed by userspace application, a variable pf_enable is used to disable pf state. Default: 0 ps_retrans - INTEGER Primary.Switchover.Max.Retrans (PSMR), it's a tunable parameter coming from section-5 "Primary Path Switchover" in rfc7829. The primary path will be changed to another active path when the path error counter on the old primary path exceeds PSMR, so that "the SCTP sender is allowed to continue data transmission on a new working path even when the old primary destination address becomes active again". Note this feature is disabled by initializing 'ps_retrans' per netns as 0xffff by default, and its value can't be less than 'pf_retrans' when changing by sysctl. Default: 0xffff 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 cookie_hmac_alg - STRING Select the hmac algorithm used when generating the cookie value sent by a listening sctp socket to a connecting client in the INIT-ACK chunk. Valid values are: * md5 * sha1 * none Ability to assign md5 or sha1 as the selected alg is predicated on the configuration of those algorithms at build time (CONFIG_CRYPTO_MD5 and CONFIG_CRYPTO_SHA1). Default: Dependent on configuration. MD5 if available, else SHA1 if available, else none. 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: rcvbuf 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 Only the first value ("min") is used, "default" and "max" are ignored. min: Minimal size of receive buffer used by SCTP socket. It is guaranteed to each SCTP socket (but not association) even under moderate memory pressure. Default: 4K sctp_wmem - vector of 3 INTEGERs: min, default, max Currently this tunable has no effect. 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/* Please see: Documentation/admin-guide/sysctl/net.rst for descriptions of these entries. /proc/sys/net/unix/* max_dgram_qlen - INTEGER The maximum length of dgram socket receive queue Default: 10
core 参数
/proc/sys/net/ipv4/vs/* Variables: am_droprate - INTEGER default 10 It sets the always mode drop rate, which is used in the mode 3 of the drop_rate defense. amemthresh - INTEGER default 1024 It sets the available memory threshold (in pages), which is used in the automatic modes of defense. When there is no enough available memory, the respective strategy will be enabled and the variable is automatically set to 2, otherwise the strategy is disabled and the variable is set to 1. backup_only - BOOLEAN 0 - disabled (default) not 0 - enabled If set, disable the director function while the server is in backup mode to avoid packet loops for DR/TUN methods. conn_reuse_mode - INTEGER 1 - default Controls how ipvs will deal with connections that are detected port reuse. It is a bitmap, with the values being: 0: disable any special handling on port reuse. The new connection will be delivered to the same real server that was servicing the previous connection. This will effectively disable expire_nodest_conn. bit 1: enable rescheduling of new connections when it is safe. That is, whenever expire_nodest_conn and for TCP sockets, when the connection is in TIME_WAIT state (which is only possible if you use NAT mode). bit 2: it is bit 1 plus, for TCP connections, when connections are in FIN_WAIT state, as this is the last state seen by load balancer in Direct Routing mode. This bit helps on adding new real servers to a very busy cluster. conntrack - BOOLEAN 0 - disabled (default) not 0 - enabled If set, maintain connection tracking entries for connections handled by IPVS. This should be enabled if connections handled by IPVS are to be also handled by stateful firewall rules. That is, iptables rules that make use of connection tracking. It is a performance optimisation to disable this setting otherwise. Connections handled by the IPVS FTP application module will have connection tracking entries regardless of this setting. Only available when IPVS is compiled with CONFIG_IP_VS_NFCT enabled. cache_bypass - BOOLEAN 0 - disabled (default) not 0 - enabled If it is enabled, forward packets to the original destination directly when no cache server is available and destination address is not local (iph->daddr is RTN_UNICAST). It is mostly used in transparent web cache cluster. debug_level - INTEGER 0 - transmission error messages (default) 1 - non-fatal error messages 2 - configuration 3 - destination trash 4 - drop entry 5 - service lookup 6 - scheduling 7 - connection new/expire, lookup and synchronization 8 - state transition 9 - binding destination, template checks and applications 10 - IPVS packet transmission 11 - IPVS packet handling (ip_vs_in/ip_vs_out) 12 or more - packet traversal Only available when IPVS is compiled with CONFIG_IP_VS_DEBUG enabled. Higher debugging levels include the messages for lower debugging levels, so setting debug level 2, includes level 0, 1 and 2 messages. Thus, logging becomes more and more verbose the higher the level. drop_entry - INTEGER 0 - disabled (default) The drop_entry defense is to randomly drop entries in the connection hash table, just in order to collect back some memory for new connections. In the current code, the drop_entry procedure can be activated every second, then it randomly scans 1/32 of the whole and drops entries that are in the SYN-RECV/SYNACK state, which should be effective against syn-flooding attack. The valid values of drop_entry are from 0 to 3, where 0 means that this strategy is always disabled, 1 and 2 mean automatic modes (when there is no enough available memory, the strategy is enabled and the variable is automatically set to 2, otherwise the strategy is disabled and the variable is set to 1), and 3 means that that the strategy is always enabled. drop_packet - INTEGER 0 - disabled (default) The drop_packet defense is designed to drop 1/rate packets before forwarding them to real servers. If the rate is 1, then drop all the incoming packets. The value definition is the same as that of the drop_entry. In the automatic mode, the rate is determined by the follow formula: rate = amemthresh / (amemthresh - available_memory) when available memory is less than the available memory threshold. When the mode 3 is set, the always mode drop rate is controlled by the /proc/sys/net/ipv4/vs/am_droprate. expire_nodest_conn - BOOLEAN 0 - disabled (default) not 0 - enabled The default value is 0, the load balancer will silently drop packets when its destination server is not available. It may be useful, when user-space monitoring program deletes the destination server (because of server overload or wrong detection) and add back the server later, and the connections to the server can continue. If this feature is enabled, the load balancer will expire the connection immediately when a packet arrives and its destination server is not available, then the client program will be notified that the connection is closed. This is equivalent to the feature some people requires to flush connections when its destination is not available. expire_quiescent_template - BOOLEAN 0 - disabled (default) not 0 - enabled When set to a non-zero value, the load balancer will expire persistent templates when the destination server is quiescent. This may be useful, when a user makes a destination server quiescent by setting its weight to 0 and it is desired that subsequent otherwise persistent connections are sent to a different destination server. By default new persistent connections are allowed to quiescent destination servers. If this feature is enabled, the load balancer will expire the persistence template if it is to be used to schedule a new connection and the destination server is quiescent. ignore_tunneled - BOOLEAN 0 - disabled (default) not 0 - enabled If set, ipvs will set the ipvs_property on all packets which are of unrecognized protocols. This prevents us from routing tunneled protocols like ipip, which is useful to prevent rescheduling packets that have been tunneled to the ipvs host (i.e. to prevent ipvs routing loops when ipvs is also acting as a real server). nat_icmp_send - BOOLEAN 0 - disabled (default) not 0 - enabled It controls sending icmp error messages (ICMP_DEST_UNREACH) for VS/NAT when the load balancer receives packets from real servers but the connection entries don't exist. pmtu_disc - BOOLEAN 0 - disabled not 0 - enabled (default) By default, reject with FRAG_NEEDED all DF packets that exceed the PMTU, irrespective of the forwarding method. For TUN method the flag can be disabled to fragment such packets. secure_tcp - INTEGER 0 - disabled (default) The secure_tcp defense is to use a more complicated TCP state transition table. For VS/NAT, it also delays entering the TCP ESTABLISHED state until the three way handshake is completed. The value definition is the same as that of drop_entry and drop_packet. sync_threshold - vector of 2 INTEGERs: sync_threshold, sync_period default 3 50 It sets synchronization threshold, which is the minimum number of incoming packets that a connection needs to receive before the connection will be synchronized. A connection will be synchronized, every time the number of its incoming packets modulus sync_period equals the threshold. The range of the threshold is from 0 to sync_period. When sync_period and sync_refresh_period are 0, send sync only for state changes or only once when pkts matches sync_threshold sync_refresh_period - UNSIGNED INTEGER default 0 In seconds, difference in reported connection timer that triggers new sync message. It can be used to avoid sync messages for the specified period (or half of the connection timeout if it is lower) if connection state is not changed since last sync. This is useful for normal connections with high traffic to reduce sync rate. Additionally, retry sync_retries times with period of sync_refresh_period/8. sync_retries - INTEGER default 0 Defines sync retries with period of sync_refresh_period/8. Useful to protect against loss of sync messages. The range of the sync_retries is from 0 to 3. sync_qlen_max - UNSIGNED LONG Hard limit for queued sync messages that are not sent yet. It defaults to 1/32 of the memory pages but actually represents number of messages. It will protect us from allocating large parts of memory when the sending rate is lower than the queuing rate. sync_sock_size - INTEGER default 0 Configuration of SNDBUF (master) or RCVBUF (slave) socket limit. Default value is 0 (preserve system defaults). sync_ports - INTEGER default 1 The number of threads that master and backup servers can use for sync traffic. Every thread will use single UDP port, thread 0 will use the default port 8848 while last thread will use port 8848+sync_ports-1. snat_reroute - BOOLEAN 0 - disabled not 0 - enabled (default) If enabled, recalculate the route of SNATed packets from realservers so that they are routed as if they originate from the director. Otherwise they are routed as if they are forwarded by the director. If policy routing is in effect then it is possible that the route of a packet originating from a director is routed differently to a packet being forwarded by the director. If policy routing is not in effect then the recalculated route will always be the same as the original route so it is an optimisation to disable snat_reroute and avoid the recalculation. sync_persist_mode - INTEGER default 0 Controls the synchronisation of connections when using persistence 0: All types of connections are synchronised 1: Attempt to reduce the synchronisation traffic depending on the connection type. For persistent services avoid synchronisation for normal connections, do it only for persistence templates. In such case, for TCP and SCTP it may need enabling sloppy_tcp and sloppy_sctp flags on backup servers. For non-persistent services such optimization is not applied, mode 0 is assumed. sync_version - INTEGER default 1 The version of the synchronisation protocol used when sending synchronisation messages. 0 selects the original synchronisation protocol (version 0). This should be used when sending synchronisation messages to a legacy system that only understands the original synchronisation protocol. 1 selects the current synchronisation protocol (version 1). This should be used where possible. Kernels with this sync_version entry are able to receive messages of both version 1 and version 2 of the synchronisation protocol.