The sysctl variables in IPVS
All the sysctl variables in IPVS are under the directory /proc/sys/net/ipv4/vs/. The following description is for the sysctl variables in IPVS 1.0.x for the Linux kernel 2.4.xx.
The /proc/sys/net/ipv4/vs/* Variables:
debug_level - INTEGER
It is only available when IPVS is compiled with the IPVS
debugging option.
The default value is 0. The higher value is set to
debug_level, the more debugging information is output in the
kernel messages. See the doc/debug-levels.txt (shipped in ipvs
source code) for more information about the debugging levels.
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.
nat_icmp_send - BOOLEAN
0 - disabled (default)
not 0 - enabled
It controlls 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.
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.
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.
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 actived 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.
secure_tcp - INTEGER
0 - disabled (default)
The secure_tcp defense is to use a more complicated state
transtition 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.
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.
am_droprate - INTEGER
default 10
It sets the always mode drop rate, which is used in the mode 3
of the drop_rate defense.
timeout_* - INTEGER
Secure TCP timeouts (in seconds).