[IPVS]: Add sysctl documentation
* Derived from http://www.linuxvirtualserver.org/docs/sysctl.html, v1.4 maintained by Wensong Zhang * Adjusted preample to match ip-sysctl.txt * Sorted options into alphabetical order * Added expire_quiescent_template * Removed timeout_* which are no longer present * Incoporated doc/debug-levels.txt from IPVS source tree into description of ipvs_debug * Minor spelling fixes * Further editing more than welcome Signed-Off-By: Horms <horms@verge.net.au> Signed-off-by: David S. Miller <davem@davemloft.net>
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Horms
David S. Miller
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/proc/sys/net/ipv4/vs/* Variables:
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am_droprate - INTEGER
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default 10
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It sets the always mode drop rate, which is used in the mode 3
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of the drop_rate defense.
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amemthresh - INTEGER
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default 1024
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It sets the available memory threshold (in pages), which is
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used in the automatic modes of defense. When there is no
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enough available memory, the respective strategy will be
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enabled and the variable is automatically set to 2, otherwise
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the strategy is disabled and the variable is set to 1.
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cache_bypass - BOOLEAN
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0 - disabled (default)
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not 0 - enabled
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If it is enabled, forward packets to the original destination
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directly when no cache server is available and destination
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address is not local (iph->daddr is RTN_UNICAST). It is mostly
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used in transparent web cache cluster.
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debug_level - INTEGER
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0 - transmission error messages (default)
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1 - non-fatal error messages
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2 - configuration
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3 - destination trash
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4 - drop entry
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5 - service lookup
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6 - scheduling
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7 - connection new/expire, lookup and synchronization
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8 - state transition
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9 - binding destination, template checks and applications
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10 - IPVS packet transmission
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11 - IPVS packet handling (ip_vs_in/ip_vs_out)
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12 or more - packet traversal
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Only available when IPVS is compiled with the CONFIG_IPVS_DEBUG
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Higher debugging levels include the messages for lower debugging
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levels, so setting debug level 2, includes level 0, 1 and 2
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messages. Thus, logging becomes more and more verbose the higher
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the level.
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drop_entry - INTEGER
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0 - disabled (default)
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The drop_entry defense is to randomly drop entries in the
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connection hash table, just in order to collect back some
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memory for new connections. In the current code, the
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drop_entry procedure can be activated every second, then it
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randomly scans 1/32 of the whole and drops entries that are in
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the SYN-RECV/SYNACK state, which should be effective against
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syn-flooding attack.
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The valid values of drop_entry are from 0 to 3, where 0 means
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that this strategy is always disabled, 1 and 2 mean automatic
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modes (when there is no enough available memory, the strategy
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is enabled and the variable is automatically set to 2,
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otherwise the strategy is disabled and the variable is set to
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1), and 3 means that that the strategy is always enabled.
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drop_packet - INTEGER
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0 - disabled (default)
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The drop_packet defense is designed to drop 1/rate packets
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before forwarding them to real servers. If the rate is 1, then
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drop all the incoming packets.
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The value definition is the same as that of the drop_entry. In
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the automatic mode, the rate is determined by the follow
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formula: rate = amemthresh / (amemthresh - available_memory)
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when available memory is less than the available memory
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threshold. When the mode 3 is set, the always mode drop rate
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is controlled by the /proc/sys/net/ipv4/vs/am_droprate.
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expire_nodest_conn - BOOLEAN
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0 - disabled (default)
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not 0 - enabled
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The default value is 0, the load balancer will silently drop
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packets when its destination server is not available. It may
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be useful, when user-space monitoring program deletes the
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destination server (because of server overload or wrong
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detection) and add back the server later, and the connections
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to the server can continue.
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If this feature is enabled, the load balancer will expire the
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connection immediately when a packet arrives and its
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destination server is not available, then the client program
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will be notified that the connection is closed. This is
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equivalent to the feature some people requires to flush
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connections when its destination is not available.
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expire_quiescent_template - BOOLEAN
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0 - disabled (default)
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not 0 - enabled
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When set to a non-zero value, the load balancer will expire
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persistent templates when the destination server is quiescent.
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This may be useful, when a user makes a destination server
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quiescent by setting its weight to 0 and it is desired that
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subsequent otherwise persistent connections are sent to a
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different destination server. By default new persistent
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connections are allowed to quiescent destination servers.
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If this feature is enabled, the load balancer will expire the
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persistence template if it is to be used to schedule a new
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connection and the destination server is quiescent.
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nat_icmp_send - BOOLEAN
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0 - disabled (default)
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not 0 - enabled
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It controls sending icmp error messages (ICMP_DEST_UNREACH)
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for VS/NAT when the load balancer receives packets from real
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servers but the connection entries don't exist.
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secure_tcp - INTEGER
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0 - disabled (default)
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The secure_tcp defense is to use a more complicated state
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transition table and some possible short timeouts of each
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state. In the VS/NAT, it delays the entering the ESTABLISHED
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until the real server starts to send data and ACK packet
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(after 3-way handshake).
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The value definition is the same as that of drop_entry or
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drop_packet.
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sync_threshold - INTEGER
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default 3
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It sets synchronization threshold, which is the minimum number
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of incoming packets that a connection needs to receive before
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the connection will be synchronized. A connection will be
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synchronized, every time the number of its incoming packets
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modulus 50 equals the threshold. The range of the threshold is
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from 0 to 49.
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