Command Line Interface Reference Guide > The SLB Configuration Menu
/cfg/slb/advhc/health <health check ID>/logexp
LOGEXP Health Check Configuration
You can set logical expressions between health checks.
 
[LOGEXP Health Check <HC ID> Menu]
name - Set descriptive logical expression name
logexp - Set logical expression between health checks
always - Enable/disable always performing the health check
copy - Copy logical expression
del - Delete logical expression
cur - Display current logical expression
 
LOGEXP Health Check Menu Options (/cfg/slb/advhc/health <health check ID>/logexp) 
Command Syntax and Usage
name
 
Sets the descriptive logical expression name.
logexp
 
Sets the logical expression between health checks.
A logical expression contains operands and at least one logical operator.
An operand is the name of a health check, space, or an operator. Operand names can contain a maximum of 32 characters.
The following logical operators are supported:
*“&” — AND
*“|” — OR
*() — Brackets
Note: Semantic evaluation of logical expressions is similar to any compiler’s Boolean expression evaluation: the “&” operator is given a higher precedence than the “|” operator.
Examples of valid logical expressions include the following:
*“arp”, “snmp”, or “icmp”.
*“arp & (snmp|icmp)”
*“arp | dns & ftp” (brackets are not required here since “&” has a higher precedence than “|”)
* “(snmp|ftp) & (sip|ldap)”
* “((snmp|ftp) & (sip|ldap)) | dns”
 
Operands must be valid before sending the apply command. Parsing of the logical expression begins only after you send the apply command. If parsing fails, the “Error: Syntax error in logical expression formula” message displays:
The apply command fails if the logical expression contains one or more of the following:
*A health check that is defined in Alteon
*A loop
*An invalid sub-expression. A sub-expression is invalid if it contains one or more of the following:
*An opening bracket followed by an operator, with no operand between them. For example, “(&”.
*An operator followed by a single operand. For example, “&http”.
*Empty brackets “()”.
*Two adjacent operands with no operator between them. For example, “http icmp”.
*Two adjacent operators. For example, “&&”.
*An operand followed by an opening bracket, with no operator and closing bracket. For example, “icmp(”.
*An operator at the end of the string, with no following operand. For example, “icmp|”.
A logical expression can contain up to 10 health check names. If more than 10 are configured, the “Error: Up to 10 health checks are supported per logical expression” message displays.
always disabled|enabled
 
Specifies that the health check is performed for real servers that are not attached to any virtual service or filter.
Default: disabled
copy
 
Copies the logical expression.
del
 
Deletes the logical expression.
cur
 
Displays the current logical expression.