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/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.
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