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

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Health Checks > Layer 4 Health Check

Layer 4 Health Check
Disabling or Re-Enabling Layer 4 Health Check
Layer 4 health checks are enabled by default.
If you are configuring the ServerIron ADX to load balance traffic to multiple servers on the other side of routers and you want to load-balance the traffic according to TCP or UDP application, you disable the Layer 4 health checks. If you do not disable the health checks in this type of configuration, the routers will fail the health checks (because the target applications for the health checks are not on the routers themselves) and the ServerIron ADX will stop forwarding traffic to those servers.
NOTE: If you are using the ServerIron ADX to load-balance TCP and UDP traffic through routers, you also must add each router as a real server and disable the HTTP port on each of the real servers. HTTP is enabled by default on all real servers.
To globally disable Layer 4 TCP or UDP health checks for servers, enter the following command:
ServerIron(config)# no server l4-check
Syntax: [no] server l4-check
Performing Layer 4 UDP Keepalive Health Checks for the DNS Port
You can configure the ServerIron ADX to perform Layer 4 UDP keepalive health checks for the DNS port (port 53).
To do this globally for the DNS port on all real servers, enter the following commands:
ServerIron(config)# server port dns
ServerIron(config-port-dns)# udp l4-check-only
To do this for the DNS port on real server r1, enter commands such as the following:
ServerIron(config)#server real r1 1.1.1.1
ServerIron(config-rs-r1)#port dns l4-check-only
Syntax: port dns l4-check-only
The port dns l4-check-only command configures the ServerIron ADX to use Layer 4 UDP keepalive health checks for the DNS port, instead of Layer 7 DNS health checks. This command applies to keepalive health checks only, not to the health check performed when the DNS port is brought up. When the DNS port on a real server is brought up, by default the ServerIron ADX performs a Layer 4 TCP health check. You can configure the ServerIron ADX to perform a Layer 4 UDP health check when the DNS port is brought up by adding the no tcp keepalive enable command to the DNS port profile. For example:
ServerIron(config)# server port dns
ServerIron(config-port-dns)# no tcp keepalive enable

Health Checks > Layer 4 Health Check

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