/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.