/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.
  
  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 the CONFIG_IPVS_DEBUG
  
  	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.
  
  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.
  
  secure_tcp - INTEGER
          0  - disabled (default)
  
          The secure_tcp defense is to use a more complicated state
          transition table and some possible short timeouts of each
          state. In the VS/NAT, it delays the entering the ESTABLISHED
          until the real server starts to send data and ACK packet
          (after 3-way handshake).
  
          The value definition is the same as that of drop_entry or
          drop_packet.
  
  sync_threshold - INTEGER
          default 3
  
          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 50 equals the threshold. The range of the threshold is
          from 0 to 49.