/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.

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.

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 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 - 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.

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.
