Provided by: ipvsadm_1.31-1ubuntu0.1_amd64 
NAME
ipvsadm - Linux Virtual Server administration
SYNOPSIS
ipvsadm -A|E virtual-service [-s scheduler]
[-p [timeout]] [-M netmask] [-b sched-flags]
ipvsadm -D virtual-service
ipvsadm -C
ipvsadm -R
ipvsadm -S [-n]
ipvsadm -a|e virtual-service -r server-address
[-g|i|m] [-w weight] [-x upper] [-y lower]
ipvsadm -d virtual-service -r server-address
ipvsadm -L|l [virtual-service] [options]
ipvsadm -Z [virtual-service]
ipvsadm --set tcp tcpfin udp
ipvsadm --start-daemon state [daemon-options]
[--syncid syncid]
ipvsadm --stop-daemon state
ipvsadm -h
DESCRIPTION
Ipvsadm(8) is used to set up, maintain or inspect the virtual server table in the Linux kernel. The Linux
Virtual Server can be used to build scalable network services based on a cluster of two or more nodes.
The active node of the cluster redirects service requests to a collection of server hosts that will
actually perform the services. Supported features include three protocols (TCP, UDP and SCTP), three
packet-forwarding methods (NAT, tunneling, and direct routing), and eight load balancing algorithms
(round robin, weighted round robin, least-connection, weighted least-connection, locality-based least-
connection, locality-based least-connection with replication, destination-hashing, and source-hashing).
The command has two basic formats for execution:
ipvsadm COMMAND virtual-service
[scheduling-method] [persistence options]
ipvsadm command virtual-service
server-address [packet-forwarding-method]
[weight options]
The first format manipulates a virtual service and the algorithm for assigning service requests to real
servers. Optionally, a persistent timeout and network mask for the granularity of a persistent service
and a persistence engine may be specified. The second format manipulates a real server that is associated
with an existing virtual service. When specifying a real server, the packet-forwarding method and the
weight of the real server, relative to other real servers for the virtual service, may be specified,
otherwise defaults will be used.
COMMANDS
ipvsadm(8) recognises the commands described below. Upper-case commands maintain virtual services. Lower-
case commands maintain real servers that are associated with a virtual service.
-A, --add-service
Add a virtual service. A service address is uniquely defined by a triplet: IP address, port
number, and protocol. Alternatively, a virtual service may be defined by a firewall-mark.
-E, --edit-service
Edit a virtual service.
-D, --delete-service
Delete a virtual service, along with any associated real servers.
-C, --clear
Clear the virtual server table.
-R, --restore
Restore Linux Virtual Server rules from stdin. Each line read from stdin will be treated as the
command line options to a separate invocation of ipvsadm. Lines read from stdin can optionally
begin with "ipvsadm". This option is useful to avoid executing a large number or ipvsadm
commands when constructing an extensive routing table.
-S, --save
Dump the Linux Virtual Server rules to stdout in a format that can be read by -R|--restore.
-a, --add-server
Add a real server to a virtual service.
-e, --edit-server
Edit a real server in a virtual service.
-d, --delete-server
Remove a real server from a virtual service.
-L, -l, --list
List the virtual server table if no argument is specified. If a service-address is selected, list
this service only. If the -c option is selected, then display the connection table. The exact
output is affected by the other arguments given.
-Z, --zero
Zero the packet, byte and rate counters in a service or all services.
--set tcp tcpfin udp
Change the timeout values used for IPVS connections. This command always takes 3 parameters,
representing the timeout values (in seconds) for TCP sessions, TCP sessions after receiving a
FIN packet, and UDP packets, respectively. A timeout value 0 means that the current timeout
value of the corresponding entry is preserved.
--start-daemon state
Start the connection synchronization daemon. The state is to indicate that the daemon is started
as master or backup. The connection synchronization daemon is implemented inside the Linux kernel.
The master daemon running at the primary load balancer multicasts changes of connections
periodically, and the backup daemon running at the backup load balancers receives multicast
message and creates corresponding connections. Then, in case the primary load balancer fails, a
backup load balancer will takeover, and it has state of almost all connections, so that almost all
established connections can continue to access the service.
The sync daemon supports IPv4 and IPv6 connections.
--stop-daemon
Stop the connection synchronization daemon.
-h, --help
Display a description of the command syntax.
virtual-service
Specifies the virtual service based on protocol/addr/port or firewall mark.
-t, --tcp-service service-address
Use TCP service. The service-address is of the form host[:port]. Host may be one of a plain IP
address or a hostname. Port may be either a plain port number or the service name of port. The
Port may be omitted, in which case zero will be used. A Port of zero is only valid if the service
is persistent as the -p|--persistent option, in which case it is a wild-card port, that is
connections will be accepted to any port.
-u, --udp-service service-address
Use UDP service. See the -t|--tcp-service for the description of the service-address.
--sctp-service service-address
Use SCTP service. See the -t|--tcp-service for the description of the service-address.
-f, --fwmark-service integer
Use a firewall-mark, an integer value greater than zero, to denote a virtual service instead of an
address, port and protocol (UDP, TCP or SCTP). The marking of packets with a firewall-mark is
configured using the -m|--mark option to iptables(8), the meta mark set value option to nft(8) or
via an eBPF program. It can be used to build a virtual service associated with the same real
servers, covering multiple IP address, port and protocol triplets. If IPv6 addresses are used, the
-6 option must be used.
Using firewall-mark virtual services provides a convenient method of grouping together different
IP addresses, ports and protocols into a single virtual service. This is useful for both
simplifying configuration if a large number of virtual services are required and grouping
persistence across what would otherwise be multiple virtual services.
PARAMETERS
The commands above accept or require zero or more of the following parameters.
-s, --scheduler scheduling-method
scheduling-method Algorithm for allocating TCP connections and UDP datagrams to real servers.
Scheduling algorithms are implemented as kernel modules. Ten are shipped with the Linux Virtual
Server:
rr - Round Robin: distributes jobs equally amongst the available real servers.
wrr - Weighted Round Robin: assigns jobs to real servers proportionally to there real servers'
weight. Servers with higher weights receive new jobs first and get more jobs than servers with
lower weights. Servers with equal weights get an equal distribution of new jobs.
lc - Least-Connection: assigns more jobs to real servers with fewer active jobs.
wlc - Weighted Least-Connection: assigns more jobs to servers with fewer jobs and relative to the
real servers' weight (Ci/Wi). This is the default.
lblc - Locality-Based Least-Connection: assigns jobs destined for the same IP address to the same
server if the server is not overloaded and available; otherwise assign jobs to servers with fewer
jobs, and keep it for future assignment.
lblcr - Locality-Based Least-Connection with Replication: assigns jobs destined for the same IP
address to the least-connection node in the server set for the IP address. If all the node in the
server set are over loaded, it picks up a node with fewer jobs in the cluster and adds it in the
sever set for the target. If the server set has not been modified for the specified time, the most
loaded node is removed from the server set, in order to avoid high degree of replication.
dh - Destination Hashing: assigns jobs to servers through looking up a statically assigned hash
table by their destination IP addresses.
sh - Source Hashing: assigns jobs to servers through looking up a statically assigned hash table
by their source IP addresses. This scheduler has two flags: sh-fallback, which enables fallback
to a different server if the selected server was unavailable, and sh-port, which adds the source
port number to the hash computation.
sed - Shortest Expected Delay: assigns an incoming job to the server with the shortest expected
delay. The expected delay that the job will experience is (Ci + 1) / Ui if sent to the ith
server, in which Ci is the number of jobs on the the ith server and Ui is the fixed service rate
(weight) of the ith server.
nq - Never Queue: assigns an incoming job to an idle server if there is, instead of waiting for a
fast one; if all the servers are busy, it adopts the Shortest Expected Delay policy to assign the
job.
fo - Weighted Failover: assigns an incoming job to the server with the highest weight that is
currently available.
ovf - Weighted Overflow: assigns an incoming job to the server with the highest weight that is
currently available and overflows to the next when active connections exceed the node's weight.
Note that this scheduler might not be suitable for UDP because it only uses active connections.
mh - Maglev Hashing: assigns incoming jobs based on Google's Maglev hashing algorithm, providing
an almost equal share of jobs to each real server and provides minimal disruption. When the set of
real servers changes, a connection will likely be sent to the same real server as it was before.
This scheduler has two flags: mh-fallback, which enables fallback to a different server if the
selected server was unavailable, and mh-port, which adds the source port number to the hash
computation.
-p, --persistent [timeout]
Specify that a virtual service is persistent. If this option is specified, multiple requests from
a client are redirected to the same real server selected for the first request. Optionally, the
timeout of persistent sessions may be specified given in seconds, otherwise the default of 300
seconds will be used. This option may be used in conjunction with protocols such as SSL or FTP
where it is important that clients consistently connect with the same real server.
Note: If a virtual service is to handle FTP connections then persistence must be set for the
virtual service if Direct Routing or Tunnelling is used as the forwarding mechanism. If
Masquerading is used in conjunction with an FTP service than persistence is not necessary, but the
ip_vs_ftp kernel module must be used. This module may be manually inserted into the kernel using
insmod(8).
-M, --netmask netmask
Specify the granularity with which clients are grouped for persistent virtual services. The
source address of the request is masked with this netmask to direct all clients from a network to
the same real server. The default is 255.255.255.255, that is, the persistence granularity is per
client host. Less specific netmasks may be used to resolve problems with non-persistent cache
clusters on the client side. IPv6 netmasks should be specified as a prefix length between 1 and
128. The default prefix length is 128.
--pe persistence-engine
Specify an alternative persistence engine to be used. Currently the only alternative persistence
engine available is sip.
-b, --sched-flags sched-flags
Set scheduler flags for this virtual server. sched-flags is a comma-separated list of flags. See
the scheduler descriptions for valid scheduler flags.
-r, --real-server server-address
Real server that an associated request for service may be assigned to. The server-address is the
host address of a real server, and may plus port. Host can be either a plain IP address or a
hostname. Port can be either a plain port number or the service name of port. In the case of the
masquerading method, the host address is usually an RFC 1918 private IP address, and the port can
be different from that of the associated service. With the tunneling and direct routing methods,
port must be equal to that of the service address. For normal services, the port specified in the
service address will be used if port is not specified. For fwmark services, port may be omitted,
in which case the destination port on the real server will be the destination port of the request
sent to the virtual service.
[packet-forwarding-method]
-g, --gatewaying Use gatewaying (direct routing). This is the default.
-i, --ipip Use ipip encapsulation (tunneling).
--tun-type tun-type
tun-type is one of ipip|gue|gre. The default value of tun-type is ipip.
--tun-port tun-port
tun-port is an integer specifying the destination port. Only valid for tun-type
gue.
--tun-nocsum
Specify that tunnel checksums are disabled. This is the default. Only valid for
tun-type gue and gre.
--tun-csum
Specify that tunnel checksums are enabled. Only valid for tun-type gue and gre.
--tun-remcsum
Specify that Remote Checksum Offload is enabled. Only valid for tun-type gue.
-m, --masquerading Use masquerading (network access translation, or NAT).
Note: Regardless of the packet-forwarding mechanism specified, real servers for addresses for
which there are interfaces on the local node will be use the local forwarding method, then packets
for the servers will be passed to upper layer on the local node. This cannot be specified by
ipvsadm, rather it set by the kernel as real servers are added or modified.
-w, --weight weight
Weight is an integer specifying the capacity of a server relative to the others in the pool. The
valid values of weight are 0 through to 2147483647. The default is 1. Quiescent servers are
specified with a weight of zero. A quiescent server will receive no new jobs but still serve the
existing jobs, for all scheduling algorithms distributed with the Linux Virtual Server. Setting a
quiescent server may be useful if the server is overloaded or needs to be taken out of service for
maintenance.
-x, --u-threshold uthreshold
uthreshold is an integer specifying the upper connection threshold of a server. The valid values
of uthreshold are 0 through to 65535. The default is 0, which means the upper connection threshold
is not set. If uthreshold is set with other values, no new connections will be sent to the server
when the number of its connections exceeds its upper connection threshold.
-y, --l-threshold lthreshold
lthreshold is an integer specifying the lower connection threshold of a server. The valid values
of lthreshold are 0 through to 65535. The default is 0, which means the lower connection threshold
is not set. If lthreshold is set with other values, the server will receive new connections when
the number of its connections drops below its lower connection threshold. If lthreshold is not set
but uthreshold is set, the server will receive new connections when the number of its connections
drops below three forth of its upper connection threshold.
-c, --connection
Connection output. The list command with this option will list current IPVS connections.
--timeout
Timeout output. The list command with this option will display the timeout values (in seconds)
for TCP sessions, TCP sessions after receiving a FIN packet, and UDP packets.
--daemon
Daemon information output. The list command with this option will display the daemon status and
its multicast interface.
--stats
Output of statistics information. The list command with this option will display the statistics
information of services and their servers.
--rate Output of rate information. The list command with this option will display the rate information
(such as connections/second, bytes/second and packets/second) of services and their servers.
--thresholds
Output of thresholds information. The list command with this option will display the upper/lower
connection threshold information of each server in service listing.
--persistent-conn
Output of persistent connection information. The list command with this option will display the
persistent connection counter information of each server in service listing. The persistent
connection is used to forward the actual connections from the same client/network to the same
server.
The list command with the -c, --connection option and this option will include persistence engine
data, if any is present, when listing connections.
--tun-info
Output of tunneling information. The list command with this option will display the tunneling
information of services and their servers.
--sort Sort the list of virtual services and real servers. The virtual service entries are sorted in
ascending order by <protocol, address, port>. The real server entries are sorted in ascending
order by <address, port>. (default)
--nosort
Do not sort the list of virtual services and real servers.
-n, --numeric
Numeric output. IP addresses and port numbers will be printed in numeric format rather than as as
host names and services respectively, which is the default.
--exact
Expand numbers. Display the exact value of the packet and byte counters, instead of only the
rounded number in K's (multiples of 1000) M's (multiples of 1000K) or G's (multiples of 1000M).
This option is only relevant for the -L command.
-6, --ipv6
Use with -f to signify fwmark rule uses IPv6 addresses.
-o, --ops
One-packet scheduling. Used in conjunction with a UDP virtual service or a fwmark virtual service
that handles only UDP packets. All connections are created such that they only schedule one
packet.
PARAMETERS FOR SYNCHRONIZATION DAEMON
The --start-daemon requires zero or more of the following parameters.
--syncid syncid
Specify the syncid that the sync master daemon fills in the SyncID header while sending multicast
messages, or the sync backup daemon uses to filter out multicast messages not matched with the
SyncID value. The valid values of syncid are 0 through to 255. The default is 0, which means no
filtering at all.
--sync-maxlen length
Specify the desired length of sync messages (UDP payload size). It is expected that backup server
will use value not less than the used value in master server. The valid values of length are in
the 1 .. (65535 - 20 - 8) range but the kernel ensures a space for at least one sync message. If
value is lower than MTU the sync messages will be fragmented by IP layer. The default value is
derived from the MTU value when daemon is started but master daemon will not default to value
above 1500 for compatibility reasons.
--mcast-interface interface
Specify the multicast interface that the sync master daemon sends outgoing multicasts through, or
the sync backup daemon listens to for multicasts.
--mcast-group address
Specify IPv4 or IPv6 multicast address for the sync messages. The default value is 224.0.0.81.
--mcast-port port
Specify the UDP port for sync messages. The default value is 8848.
--mcast-ttl ttl
Specify the TTL value for sync messages (1 .. 255). The default value is 1.
EXAMPLE 1 - Simple Virtual Service
The following commands configure a Linux Director to distribute incoming requests addressed to port 80 on
207.175.44.110 equally to port 80 on five real servers. The forwarding method used in this example is
NAT, with each of the real servers being masqueraded by the Linux Director.
ipvsadm -A -t 207.175.44.110:80 -s rr
ipvsadm -a -t 207.175.44.110:80 -r 192.168.10.1:80 -m
ipvsadm -a -t 207.175.44.110:80 -r 192.168.10.2:80 -m
ipvsadm -a -t 207.175.44.110:80 -r 192.168.10.3:80 -m
ipvsadm -a -t 207.175.44.110:80 -r 192.168.10.4:80 -m
ipvsadm -a -t 207.175.44.110:80 -r 192.168.10.5:80 -m
Alternatively, this could be achieved in a single ipvsadm command.
echo "
-A -t 207.175.44.110:80 -s rr
-a -t 207.175.44.110:80 -r 192.168.10.1:80 -m
-a -t 207.175.44.110:80 -r 192.168.10.2:80 -m
-a -t 207.175.44.110:80 -r 192.168.10.3:80 -m
-a -t 207.175.44.110:80 -r 192.168.10.4:80 -m
-a -t 207.175.44.110:80 -r 192.168.10.5:80 -m
" | ipvsadm -R
As masquerading is used as the forwarding mechanism in this example, the default route of the real
servers must be set to the linux director, which will need to be configured to forward and masquerade
packets. This can be achieved using the following commands:
echo "1" > /proc/sys/net/ipv4/ip_forward
EXAMPLE 2 - Firewall-Mark Virtual Service
The following commands configure a Linux Director to distribute incoming requests addressed to any port
on 207.175.44.110 or 207.175.44.111 equally to the corresponding port on five real servers. As per the
previous example, the forwarding method used in this example is NAT, with each of the real servers being
masqueraded by the Linux Director.
ipvsadm -A -f 1 -s rr
ipvsadm -a -f 1 -r 192.168.10.1:0 -m
ipvsadm -a -f 1 -r 192.168.10.2:0 -m
ipvsadm -a -f 1 -r 192.168.10.3:0 -m
ipvsadm -a -f 1 -r 192.168.10.4:0 -m
ipvsadm -a -f 1 -r 192.168.10.5:0 -m
As masquerading is used as the forwarding mechanism in this example, the default route of the real
servers must be set to the linux director, which will need to be configured to forward and masquerade
packets. The real server should also be configured to mark incoming packets addressed to any port on
207.175.44.110 and 207.175.44.111 with firewall-mark 1. If FTP traffic is to be handled by this virtual
service, then the ip_vs_ftp kernel module needs to be inserted into the kernel. These operations can be
achieved using the following commands:
echo "1" > /proc/sys/net/ipv4/ip_forward
modprobe ip_tables
iptables -A PREROUTING -t mangle -d 207.175.44.110/31 -j MARK --set-mark 1
modprobe ip_vs_ftp
EXAMPLE 3 - Virtual Service with GUE Tunneling
The following commands configure a Linux Director to distribute incoming requests addressed to port 80 on
207.175.44.110 equally to port 80 on five real servers. The forwarding method used in this example is
tunneling with gue encapsulation.
ipvsadm -A -t 207.175.44.110:80 -s rr
ipvsadm -a -t 207.175.44.110:80 -r 192.168.10.1:80 -i --tun-type gue --tun-port 6080 --tun-nocsum
ipvsadm -a -t 207.175.44.110:80 -r 192.168.10.2:80 -i --tun-type gue --tun-port 6080 --tun-csum
ipvsadm -a -t 207.175.44.110:80 -r 192.168.10.3:80 -i --tun-type gue --tun-port 6080 --tun-remcsum
ipvsadm -a -t 207.175.44.110:80 -r 192.168.10.4:80 -i --tun-type gue --tun-port 6078
ipvsadm -a -t 207.175.44.110:80 -r 192.168.10.5:80 -i --tun-type gue --tun-port 6079
Alternatively, this could be achieved in a single ipvsadm command.
echo "
-A -t 207.175.44.110:80 -s rr
-a -t 207.175.44.110:80 -r 192.168.10.1:80 -i --tun-type gue --tun-port 6080 --tun-nocsum
-a -t 207.175.44.110:80 -r 192.168.10.2:80 -i --tun-type gue --tun-port 6080 --tun-csum
-a -t 207.175.44.110:80 -r 192.168.10.3:80 -i --tun-type gue --tun-port 6080 --tun-remcsum
-a -t 207.175.44.110:80 -r 192.168.10.4:80 -i --tun-type gue --tun-port 6078
-a -t 207.175.44.110:80 -r 192.168.10.5:80 -i --tun-type gue --tun-port 6079
" | ipvsadm -R
EXAMPLE 4 - Virtual Service with GRE Tunneling
The following commands configure a Linux Director to use GRE encapsulation.
ipvsadm -A -t 10.0.0.1:80 -s rr
ipvsadm -a -t 10.0.0.1:80 -r 192.168.11.1:80 -i --tun-type gre --tun-csum
IPv6
IPv6 addresses should be surrounded by square brackets ([ and ]).
ipvsadm -A -t [2001:db8::80]:80 -s rr
ipvsadm -a -t [2001:db8::80]:80 -r [2001:db8::a0a0]:80 -m
fwmark IPv6 services require the -6 option.
NOTES
The Linux Virtual Server implements three defense strategies against some types of denial of service
(DoS) attacks. The Linux Director creates an entry for each connection in order to keep its state, and
each entry occupies 128 bytes effective memory. LVS's vulnerability to a DoS attack lies in the potential
to increase the number entries as much as possible until the linux director runs out of memory. The three
defense strategies against the attack are: Randomly drop some entries in the table. Drop 1/rate packets
before forwarding them. And use secure tcp state transition table and short timeouts. The strategies are
controlled by sysctl variables and corresponding entries in the /proc filesystem:
/proc/sys/net/ipv4/vs/drop_entry /proc/sys/net/ipv4/vs/drop_packet /proc/sys/net/ipv4/vs/secure_tcp
Valid values for each variable are 0 through to 3. The default value is 0, which disables the respective
defense strategy. 1 and 2 are automatic modes - 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. A value of 3 denotes that the respective strategy is always enabled. The
available memory threshold and secure TCP timeouts can be tuned using the sysctl variables and
corresponding entries in the /proc filesystem:
/proc/sys/net/ipv4/vs/amemthresh /proc/sys/net/ipv4/vs/timeout_*
FILES
/proc/net/ip_vs
/proc/net/ip_vs_app
/proc/net/ip_vs_conn
/proc/net/ip_vs_stats
/proc/sys/net/ipv4/vs/am_droprate
/proc/sys/net/ipv4/vs/amemthresh
/proc/sys/net/ipv4/vs/drop_entry
/proc/sys/net/ipv4/vs/drop_packet
/proc/sys/net/ipv4/vs/secure_tcp
/proc/sys/net/ipv4/vs/timeout_close
/proc/sys/net/ipv4/vs/timeout_closewait
/proc/sys/net/ipv4/vs/timeout_established
/proc/sys/net/ipv4/vs/timeout_finwait
/proc/sys/net/ipv4/vs/timeout_icmp
/proc/sys/net/ipv4/vs/timeout_lastack
/proc/sys/net/ipv4/vs/timeout_listen
/proc/sys/net/ipv4/vs/timeout_synack
/proc/sys/net/ipv4/vs/timeout_synrecv
/proc/sys/net/ipv4/vs/timeout_synsent
/proc/sys/net/ipv4/vs/timeout_timewait
/proc/sys/net/ipv4/vs/timeout_udp
SEE ALSO
The LVS web site (http://www.linuxvirtualserver.org/) for more documentation about LVS.
ipvsadm-save(8), ipvsadm-restore(8), iptables(8),
insmod(8), modprobe(8)
AUTHORS
ipvsadm - Wensong Zhang <wensong@linuxvirtualserver.org>
Peter Kese <peter.kese@ijs.si>
man page - Mike Wangsmo <wanger@redhat.com>
Wensong Zhang <wensong@linuxvirtualserver.org>
Horms <horms@verge.net.au>
4th Berkeley Distribution 5th July 2003 IPVSADM(8)