Table Of Contents
Server Load Balancing Commands
Server Load Balancing Commands
Use the commands in this chapter to configure the IOS Server Load Balancing (SLB) feature. For configuration information and examples, refer to the "Configuring Server Load Balancing" chapter of the Cisco IOS IP Configuration Guide.
advertise
To control the installation of a static route to the Null0 interface for a virtual server address, use the advertise SLB virtual server configuration command. To prevent the installation of a static route for the virtual server IP address, use the no form of this command.
advertise
no advertise
Syntax Description
This command has no arguments or keywords.
Defaults
The SLB virtual server IP address is added to the routing table.
Command Modes
SLB virtual server configuration
Command History
12.0(7)XE
This command was introduced.
12.1(5)T
This command was integrated into Cisco IOS Release 12.1(5)T.
Usage Guidelines
By default, virtual server addresses are advertised. That is, static routes to the Null0 interface are installed for the virtual server addresses.
Advertisement of this static route using the routing protocol requires that you configure redistribution of static routes for the routing protocol.
Examples
The following example prevents advertisement of the IP address of the virtual server in routing protocol updates:
ip slb vserver PUBLIC_HTTPno advertiseRelated Commands
agent
To configure a Dynamic Feedback Protocol (DFP) agent, use the agent SLB DFP configuration command. To remove an agent definition from the DFP configuration, use the no form of this command.
agent ip-address port [timeout [retry-count [retry-interval]]]
no agent ip-address port
Syntax Description
Defaults
The default timeout is 0 seconds (no timeout).
The default retry count is 0 (infinite retries).
The default retry interval is 180 seconds.
Command Modes
SLB DFP configuration
Command History
12.0(7)XE
This command was introduced.
12.1(5)T
This command was integrated into Cisco IOS Release 12.1(5)T.
Usage Guidelines
You can configure up to 1024 agents.
A DFP agent collects status information about the load capability of a server and reports that information to a load manager. The DFP agent may reside on the server, or it may be a separate device that collects and consolidates the information from several servers before reporting to the load manager.
Examples
The following example configures a DFP agent on the DFP manager, sets the DFP password to Cookies and the timeout to 360 seconds, changes the configuration mode to DFP configuration mode, sets the IP address of the DFP agent to 10.1.1.1, and sets the port number of the DFP agent to 2221 (FTP):
ip slb dfp password Cookies 360agent 10.1.1.1 2221Related Commands
bindid
To configure a bind ID, use the bindid SLB server farm configuration command. To remove a bind ID from the server farm configuration, use the no form of this command.
bindid [bind-id]
no bindid [bind-id]
Syntax Description
Defaults
The default bind ID is 0.
Command Modes
SLB server farm configuration
Command History
12.0(7)XE
This command was introduced.
12.1(5)T
This command was integrated into Cisco IOS Release 12.1(5)T.
Usage Guidelines
You can configure one bind ID on each bindid command.
The bind ID allows a single physical server to be bound to multiple virtual servers and report a different weight for each one. Thus, the single real server is represented as multiple instances of itself, each having a different bind ID. DFP uses the bind ID to identify for which instance of the real server a given weight is specified.
Examples
The following example configures bind ID 309:
ip slb serverfarm PUBLICbindid 309Related Commands
clear ip slb
To clear IP IOS SLB connections or counters, use the clear ip slb privileged EXEC command.
clear ip slb {connections [serverfarm farm-name | vserver server-name] | counters}
Syntax Description
Defaults
No default behavior or values.
Command Modes
Privileged EXEC
Command History
12.1(1)E
This command was introduced.
12.1(5)T
This command was integrated into Cisco IOS Release 12.1(5)T.
Examples
The following example clears the connection database of the server farm named FARM1:
Router# clear ip slb connections serverfarm FARM1The following example clears the connection database of the virtual server named VSERVER1:
Router# clear ip slb connections vserver VSERVER1The following example clears the IOS SLB counters:
Router# clear ip slb countersRelated Commands
Displays information about the IOS SLB connections.
Displays information about the IOS SLB server farms.
Displays information about the IOS SLB virtual servers.
client
To define which clients are allowed to use the virtual server, use the client SLB virtual server configuration command. You can use more than one client command to define more than one client. To remove a client definition from the IOS SLB configuration, use the no form of this command.
client ip-address network-mask
no client ip-address network-mask
Syntax Description
ip-address
Client IP address. The default is 0.0.0.0 (all clients).
network-mask
Client IP network mask. The default is 0.0.0.0 (all subnetworks).
Defaults
The default IP address is 0.0.0.0 (all clients).
The default network mask is 0.0.0.0 (all subnetworks).
Taken together, the default is client 0.0.0.0 0.0.0.0 (allows all clients on all subnetworks to use the virtual server).
Command Modes
SLB virtual server configuration
Command History
12.0(7)XE
This command was introduced.
12.1(5)T
This command was integrated into Cisco IOS Release 12.1(5)T.
Usage Guidelines
The network-mask value is applied to the source IP address of incoming connections. The result must match the ip-address value for the client to be allowed to use the virtual server.
Examples
The following example allows only clients from 10.4.4.x access to the virtual server:
ip slb vserver PUBLIC_HTTPclient 10.4.4.0 255.255.255.0Related Commands
Displays information about the virtual servers.
Configures the virtual server attributes.
delay (virtual server)
To change the amount of time the IOS SLB feature maintains TCP connection context after a connection has terminated, use the delay SLB virtual server configuration command. To restore the default delay timer, use the no form of this command.
delay duration
no delay
Syntax Description
duration
Delay timer duration in seconds. The valid range is from 1 to 600 seconds. The default value is 10 seconds.
Defaults
The default duration is 10 seconds.
Command Modes
SLB virtual server configuration
Command History
12.0(7)XE
This command was introduced.
12.1(5)T
This command was integrated into Cisco IOS Release 12.1(5)T.
Usage Guidelines
The delay timer allows out-of-sequence packets and final acknowledgments (ACKs) to be delivered after a TCP connection ends.
Do not set this value to zero (0).
If you are configuring a delay timer for HTTP flows, choose a low number such as 5 seconds as a starting point.
Examples
The following example specifies that the IOS SLB feature maintains TCP connection context for 30 seconds after a connection has terminated:
ip slb vserver PUBLIC_HTTPdelay 30Related Commands
Displays information about the virtual servers.
Configures the virtual server attributes.
faildetect
To specify the conditions that indicate a server failure, use the faildetect SLB real server configuration command. To restore the default values that indicate a server failure, use the no form of this command.
faildetect numconns number-conns [numclients number-clients]
no faildetect
Syntax Description
Defaults
If you do not specify the faildetect command, the default value of the connection reassignment threshold is 8.
If you do not specify the numclients keyword, the default value of the unique client failure threshold is 2.
Command Modes
SLB real server configuration
Command History
12.0(7)XE
This command was introduced.
12.1(5)T
This command was integrated into Cisco IOS Release 12.1(5)T.
Examples
In the following example the connection reassignment threshold is set to 16 and, because the numclients keyword is not configured, the threshold for unique client connection failure is set to the default value 8. The real server is considered to have failed when 8 unique clients have had connection failures and there have been 16 connection reassignments.
ip slb serverfarm PUBLICreal 10.10.1.1faildetect numconns 16Related Commands
Identifies a real server.
Displays information about the real servers.
Displays information about the server farm configuration.
idle
To specify the minimum amount of time for which IOS SLB maintains connection information in the absence of packet activity, use the idle virtual server configuration command. To restore the default idle duration value, use the no form of this command.
idle duration
no idle
Syntax Description
duration
Idle connection timer duration (in seconds). Valid values range from 10 to 65535. The default is 3600 seconds (1 hour).
Defaults
The default duration is 3600 seconds.
Command Modes
SLB virtual server configuration
Command History
12.0(7)XE
This command was introduced.
12.1(5)T
This command was integrated into Cisco IOS Release 12.1(5)T.
Usage Guidelines
TCP connections that do not send flows or keepalives before the idle timer expires are assumed to be inactive and are reset (RST).
If you are configuring an idle timer for HTTP flows, choose a low number such as 120 seconds as a starting point. A low number ensures that the IOS SLB connection database maintains a manageable size if problems at the server, client, or network result in a large number of connections. However, do not choose a value under 60 seconds; such a low value can reduce the efficiency of the IOS SLB feature.
Examples
The following example instructs the IOS SLB feature to maintain connection information for an idle connection for 120 seconds:
ip slb vserver PUBLIC_HTTPidle 120Related Commands
Displays information about the virtual servers.
Configures the virtual server attributes.
inservice (real server)
To enable the real server for use by the IOS SLB feature, use the inservice SLB real server configuration command. To remove the real server from service, use the no form of this command.
inservice
no inservice
Syntax Description
This command has no arguments or keywords.
Defaults
If you do not specify the inservice command, the real server is defined to IOS SLB but is not used.
Command Modes
SLB real server configuration
Command History
12.0(7)XE
This command was introduced.
12.1(5)T
This command was integrated into Cisco IOS Release 12.1(5)T.
Examples
The following example enables the real server for use by the IOS SLB feature:
ip slb serverfarm PUBLICreal 10.10.1.1inserviceRelated Commands
Identifies a real server.
Displays information about the real servers.
Displays information about the server farm configuration.
inservice (virtual server)
To enable the virtual server for use by the IOS SLB feature, use the inservice SLB virtual server configuration command. To remove the virtual server from service, use the no form of this command.
inservice [standby group-name]
no inservice [standby group-name]
Syntax Description
standby
(Optional) Configures the Hot Standby Router Protocol (HSRP) standby virtual server.
group-name
(Optional) Specifies the HSRP group name with which the IOS SLB virtual server is associated.
Defaults
If you do not specify the inservice command, the virtual server is defined to IOS SLB but is not used.
Command Modes
SLB virtual server configuration
Command History
12.0(7)XE
This command was introduced.
12.1(1)E
The standby keyword and group-name argument were added.
12.1(5)T
This command was integrated into Cisco IOS Release 12.1(5)T.
Examples
The following example enables the real server for use by the IOS SLB feature:
ip slb vserver PUBLIC_HTTPinserviceRelated Commands
Displays information about the virtual servers.
Configures the virtual server attributes.
ip slb dfp
To configure the Dynamic Feedback Protocol (DFP) and supply an optional password, use the ip slb dfp global configuration command. To remove the DFP configuration, use the no form of this command.
ip slb dfp [password password [timeout]]
no ip slb dfp
Syntax Description
Defaults
The password timeout default is 180 seconds.
Command Modes
Global configuration
Command History
12.0(7)XE
This command was introduced.
12.1(5)T
This command was integrated into Cisco IOS Release 12.1(5)T.
Usage Guidelines
The optional password, if configured, must match the password configured on the host agent.
The timeout option allows you to change the password without stopping messages between the DFP agent and its manager. The default value is 180 seconds.
During the timeout, the agent sends packets with the old password (or null, if there is no old password), and receives packets with either the old or new password. After the timeout expires, the agent sends and receives packets only with the new password; received packets that use the old password are discarded.
If you are changing the password for an entire load-balanced environment, set a longer timeout. This setting allows enough time for you to update the password on all agents and servers before the timeout expires. It also prevents mismatches between agents and servers that have begun running the new password and agents, and servers on which you have not yet changed the old password.
Examples
The following example configures DFP, sets the password to flounder, configures a timeout period of 60 seconds, and changes to DFP configuration mode:
ip slb dfp flounder 60Related Commands
ip slb serverfarm
To identify a server farm and enter SLB server farm configuration mode, use the ip slb serverfarm global configuration command. To remove the server farm from the IOS SLB configuration, use the no form of this command.
ip slb serverfarm serverfarm-name
no ip slb serverfarm serverfarm-name
Syntax Description
serverfarm-name
Character string used to identify the server farm. The character string is limited to 15 characters.
Defaults
No default behavior or values.
Command Modes
Global configuration
Command History
12.0(7)XE
This command was introduced.
12.1(5)T
This command was integrated into Cisco IOS Release 12.1(5)T.
Examples
The following example identifies a server farm named PUBLIC:
ip slb serverfarm PUBLICRelated Commands
ip slb vserver
To identify a virtual server and enter SLB virtual server configuration mode, use the ip slb vserver global configuration command. To remove a virtual server from the IOS SLB configuration, use the no form of this command.
ip slb vserver virtserver-name
no ip slb vserver virtserver-name
Syntax Description
virtserver-name
Character string used to identify the virtual server. The character string is limited to 15 characters.
Defaults
No default behavior or values.
Command Modes
Global configuration
Command History
12.0(7)XE
This command was introduced.
12.1(5)T
This command was integrated into Cisco IOS Release 12.1(5)T.
Examples
The following example identifies a virtual server named PUBLIC_HTTP:
ip slb vserver PUBLIC_HTTPRelated Commands
Associates a real server farm with a virtual server.
Displays information about the virtual servers.
maxconns (server farm)
To limit the number of active connections to the real server, use the maxconns command in SLB server farm configuration mode. To restore the default of 4294967295, use the no form of this command.
maxconns maximum-number [sticky-override]
no maxconns
Syntax Description
Defaults
The default maximum number of simultaneous active connections on the real server is 4294967295.
Command Modes
SLB server farm configuration
Command History
Examples
The following example limits the real server to a maximum of 1000 simultaneous active connections:
Router(config)# ip slb serverfarm PUBLICRouter(config-slb-sfarm)# real 10.10.1.1Router(config-slb-real)# maxconns 1000Related Commands
nat
To configure IOS SLB Network Address Translation (NAT) and specify a NAT mode, use the nat SLB server farm configuration command. To remove a NAT configuration, use the no form of this command.
nat server
no nat server
Syntax Description
server
Specifies that the destination address in load-balanced packets sent to the real server is the address of the real server chosen by the server farm load-balancing algorithm.
Defaults
No IOS SLB NAT is configured.
Command Modes
SLB server farm configuration
Command History
12.1(1)E
This command was introduced.
12.1(5)T
This command was integrated into Cisco IOS Release 12.1(5)T.
Usage Guidelines
The no nat command is allowed only if the virtual server was removed from service with the no inservice command.
Examples
The following example changes to IOS SLB server farm configuration mode and configures NAT mode as server address translation on the server farm named FARM2:
ip slb serverfarm FARM2nat serverRelated Commands
Associates a real server farm with a virtual server.
Identifies a real server as a member of a server farm.
Displays information about the server farm configuration.
predictor
To specify the load-balancing algorithm for selecting a real server in the server farm, use the predictor SLB server farm configuration command. To restore the default load-balancing algorithm of weighted round robin, use the no form of this command.
predictor [roundrobin | leastconns]
no predictor
Syntax Description
Defaults
The default predictor is weighted round robin.
Command Modes
SLB server farm configuration
Command History
12.0(7)XE
This command was introduced.
12.1(5)T
This command was integrated into Cisco IOS Release 12.1(5)T.
Examples
The following example specifies the weighted least connections algorithm:
ip slb serverfarm PUBLICpredictor leastconnsRelated Commands
Displays information about the server farm configuration.
Specifies the capacity of the real server, relative to other real servers in the server farm.
real
To identify a real server as a member of a server farm, use the real SLB server farm configuration command. To remove the real server from the IOS SLB configuration, use the no form of this command.
real ip-address
no real ip-address
Syntax Description
Defaults
No default behavior or values.
Command Modes
SLB server farm configuration
Command History
12.0(7)XE
This command was introduced.
12.1(5)T
This command was integrated into Cisco IOS Release 12.1(5)T.
Examples
The following example identifies a real server as a member of the server farm:
ip slb serverfarm PUBLICreal 10.1.1.1Related Commands
Enables the real server for use by IOS SLB.
Displays information about the server farm configuration.
Displays information about the real servers.
reassign
To specify the threshold of consecutive unanswered synchronizations that, if exceeded, results in an attempted connection to a different real server, use the reassign SLB real server configuration command. To restore the default reassignment threshold, use the no form of this command.
reassign threshold
no reassign
Syntax Description
threshold
Number of unanswered TCP SYNs that are directed to a real server before the connection is reassigned to a different real server. An unanswered SYN is one for which no SYN or ACK is detected before the next SYN arrives from the client. IOS SLB allows 30 seconds for the connection to be established or for a new SYN to be received. If neither of these events occurs within that time, the connection is removed from the IOS SLB database.
The 30-second timer is restarted for each SYN as long as the number of connection reassignments specified on the faildetect command's numconns keyword is not exceeded. See the faildetect command for more information.
Valid threshold values range from 1 to 4 SYNs. The default value is 3.
Defaults
The default threshold is three SYNs.
Command Modes
SLB real server configuration
Command History
12.0(7)XE
This command was introduced.
12.1(5)T
This command was integrated into Cisco IOS Release 12.1(5)T.
Examples
The following example sets the threshold of unanswered SYNs to 2:
ip slb serverfarm PUBLICreal 10.10.1.1reassign 2Related Commands
Identifies a real server.
Displays information about the real servers.
Displays information about the server farm configuration.
retry (real server)
To specify how long to wait before a new connection is attempted to a failed server, use the retry SLB real server configuration command. To restore the default retry value, use the no form of this command.
retry retry-value
no retry
Syntax Description
Defaults
The retry-value default is 60 seconds.
Command Modes
SLB real server configuration
Command History
12.0(7)XE
This command was introduced.
12.1(5)T
This command was integrated into Cisco IOS Release 12.1(5)T.
Examples
The following example specifies that 120 seconds must elapse after the detection of a server failure before a new connection is attempted:
ip slb serverfarm PUBLICreal 10.10.1.1retry 120Related Commands
Identifies a real server.
Displays information about the real servers.
Displays information about the server farm configuration.
serverfarm
To associate a real server farm with a virtual server, use the serverfarm SLB virtual server configuration command. To remove the server farm association from the virtual server configuration, use the no form of this command.
serverfarm serverfarm-name
no serverfarm
Syntax Description
serverfarm-name
Name of a server farm that has already been defined using the ip slb serverfarm command.
Defaults
No default behavior or values.
Command Modes
SLB virtual server configuration
Command History
12.0(7)XE
This command was introduced.
12.1(5)T
This command was integrated into Cisco IOS Release 12.1(5)T.
Examples
The following example shows how the ip slb vserver, virtual, and serverfarm commands are used to associate the real server farm named PUBLIC with the virtual server named PUBLIC_HTTP:
ip slb vserver PUBLIC_HTTPvirtual 10.0.0.1 tcp wwwserverfarm PUBLICRelated Commands
Displays information about the virtual servers.
Configures the virtual server attributes.
show ip slb conns
To display the active IOS SLB connections, use the show ip slb conns privileged EXEC command.
show ip slb conns [vserver virtserver-name] [client ip-address] [detail]
Syntax Description
Defaults
If no options are specified, the command displays output for all active IOS SLB connections.
Command Modes
Privileged EXEC
Command History
12.0(7)XE
This command was introduced.
12.1(5)T
This command was integrated into Cisco IOS Release 12.1(5)T.
Examples
The following example shows IOS SLB active connection data:
router# show ip slb connsvserver prot client real state----------------------------------------------------------------------------TEST TCP 7.150.72.183:328 80.80.90.25:80 CLOSINGTEST TCP 7.250.167.226:423 80.80.90.26:80 CLOSINGTEST TCP 7.234.60.239:317 80.80.90.26:80 CLOSINGTEST TCP 7.110.233.96:747 80.80.90.26:80 CLOSINGTEST TCP 7.162.0.201:770 80.80.90.30:80 CLOSINGTEST TCP 7.22.225.219:995 80.80.90.26:80 CLOSINGTEST TCP 7.2.170.148:169 80.80.90.30:80 CLOSINGTable 31 describes the significant fields shown in the display.
Table 31 show ip slb conns Field Descriptions
show ip slb dfp
To display DFP manager and agent information such as passwords, timeouts, retry counts, and weights, use the show ip slb dfp privileged EXEC command.
show ip slb dfp [agent ip-address port-number | detail | weights]
Syntax Description
Defaults
If no options are specified, the command displays summary information.
Command Modes
Privileged EXEC
Command History
12.0(7)XE
This command was introduced.
12.1(5)T
This command was integrated into Cisco IOS Release 12.1(5)T.
Examples
The following example shows IOS SLB DFP data:
router# show ip slb dfp detailDFP Manager:Current passwd:NONE Pending passwd:NONEPasswd timeout:0 secUned errors:0DFP Agent 161.44.2.34:61936 Connection state:ConnectedTimeout = 0 Retry Count = 0 Interval = 180 (Default)Security errors = 0Last message received:10:20:26 UTC 11/02/99Last reported Real weights for Protocol TCP, Port wwwHost 17.17.17.17 1 Weight 1Host 68.68.68.68 Bind ID 4 Weight 4Host 85.85.85.85 Bind ID 5 Weight 5Last reported Real weights for Protocol TCP, Port 22Host 17.17.17.17 Bind ID 111 Weight 111router# show ip slb dfp weightsReal IP Address 17.17.17.17 Protocol TCP Port 22 Bind_ID 111 Weight 111Set by Agent 161.44.2.3458490 at 132241 UTC 12/03/99Real IP Address 17.17.17.17 Protocol TCP Port www Bind_ID 1 Weight 1Set by Agent 161.44.2.3458490 at 132241 UTC 12/03/99Real IP Address 68.68.68.68 Protocol TCP Port www Bind_ID 4 Weight 4Set by Agent 161.44.2.3458490 at 132241 UTC 12/03/99Real IP Address 85.85.85.85 Protocol TCP Port www Bind_ID 5 Weight 5Set by Agent 161.44.2.3458490 at 132241 UTC 12/03/99router# show ip slb dfpDFP Manager:Current passwd:NONE Pending passwd:NONEPasswd timeout:0 secAgent IP Port Timeout Retry Count Interval---------------------------------------------------------------161.44.2.34 61936 0 0 180 (Default)Table 32 describes the signific
CLOSING—IOS SLB TCP connection deactivated (awaiting a delay timeout before cleaning up the connection).