ServerIron ADX Server Load Balancing Guide
Release 12.0.00
June 15, 2009

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Health Checks > Layer 3 Health Check

Layer 3 Health Check
Disabling Layer 3 Health Check
By default, when you add a real server configuration to the ServerIron ADX, the ServerIron ADX uses a Layer 3 health check (IP ping) to determine the server’s reachability. If the real server responds to the ping, the ServerIron ADX changes the server’s state to ACTIVE and begins using the server for client requests.
You can globally disable the Layer 3 health check for local servers or remote servers. You also can disable the Layer 3 health check on individual real servers. When you disable the Layer 3 health check, the ServerIron ADX sends an ARP request for the default gateway and makes the server’s state ACTIVE as long as the ARP entry is present in the ServerIron ADX’s ARP cache.
To globally disable the Layer 3 health check for all local real servers, enter the following command:
ServerIron(config)# server no-real-l3-check
Syntax: [no] server no-real-l3-check
To globally disable Layer 3 health check for all remote real servers or of IPs learned through GSLB , enter the following command:
ServerIron(config)# server no-remote-l3-check
Syntax: [no] server no-remote-l3-check
NOTE: The server no-remote-l3-check command also disables Layer3 health checks of IPs learned through GSLB.
To disable the Layer 3 health check on an individual real server, enter the following command:
ServerIron(config-rs-R1)# no-l3-check
Syntax: [no] no-l3-check
This command applies to local real servers and remote real servers.
Modifying the Ping Interval and Ping Retries
The ServerIron ADX automatically uses a Layer 3 health check consisting of ICMP echo requests (pings) to check the health of a real server. Ping is enabled by default and cannot be disabled. However, you can modify the ping interval and number of retries.
To modify the ping interval, enter the following command:
ServerIron(config)# server ping-interval 8
Syntax: [no] server ping-interval <value>
The <value> variable can be a value from 1 – 10 seconds. The default is 2 seconds.
To modify the number of times the ServerIron ADX will ping a real server before changing the server state to FAILED, enter the following command:
ServerIron(config)# server ping-retries 7
Syntax: [no] server ping-retries <value>
The <value> variable can be a value from 2 – 10. The default retry value is 4.
Setting the Periodic ARP Interval
You can configure the periodic ARP interval with a CLI command. The default interval for periodic ARPs is 20 seconds.
Server Periodic-ARP Enhancement
To configure the periodic-arp range, use the following command:
ServerIron(config)# server periodic-arp 14400
Syntax: Server periodic-arp <10-14400>
To set the periodic ARP interval, enter the following command:
ServerIron(config)# server periodic-arp-interval 60
Syntax: [no] server periodic-arp-interval <seconds>
Periodic ARPs are enabled by default. The periodic ARP interval can be from 10 – 100 seconds.
To disable periodic ARPs, enter the following command:
ServerIron(config)# server no-periodic-arp
Syntax: [no] server no-periodic-arp
Displaying Debugging Information about Periodic ARPs
To display debugging information about periodic ARPs, enter the following command:
ServerIron# debug arp periodic-arp
ARP: periodic-arp debugging is on
Syntax: debug arp periodic-arp
After you enter this command, messages such as the following are displayed on the destination specified for debug output:
Sending periodic ARP to 1.1.1.15
Sending periodic ARP to 1.1.1.15
Sending periodic ARP to 1.1.1.15

Health Checks > Layer 3 Health Check

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