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linux/Documentation/networking/ipvs-sysctl.txt
Julian Anastasov 0c12582fbc ipvs: add backup_only flag to avoid loops 
Dmitry Akindinov is reporting for a problem where SYNs are looping
between the master and backup server when the backup server is used as
real server in DR mode and has IPVS rules to function as director.

Even when the backup function is enabled we continue to forward
traffic and schedule new connections when the current master is using
the backup server as real server. While this is not a problem for NAT,
for DR and TUN method the backup server can not determine if a request
comes from client or from director.

To avoid such loops add new sysctl flag backup_only. It can be needed
for DR/TUN setups that do not need backup and director function at the
same time. When the backup function is enabled we stop any forwarding
and pass the traffic to the local stack (real server mode). The flag
disables the director function when the backup function is enabled.

For setups that enable backup function for some virtual services and
director function for other virtual services there should be another
more complex solution to support DR/TUN mode, may be to assign
per-virtual service syncid value, so that we can differentiate the
requests.

Reported-by: Dmitry Akindinov <dimak@stalker.com>
Tested-by: German Myzovsky <lawyer@sipnet.ru>
Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Simon Horman <horms@verge.net.au>
2013-03-19 21:21:51 +09:00

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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.
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_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.
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