/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.

	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.
