Chapter 3 Configuring Advanced Expressions: Getting Started 43
Which expression prefixes you can specify depends on the NetScaler feature. The
following table describes the expression prefixes that are of interest on a per-
feature basis.
Note: For details on the permitted expression prefixes in a feature, see the
documentation for that feature.
Single-Element Expressions
The simplest type of advanced expression contains a single element. This element
can be one of the following:
•true. An advanced expression can consist simply of the value true. This
type of expression always returns a value of TRUE. It is useful for chaining
policy actions and triggering Goto expressions.
•false. An advanced expression can consist simply of the value false.
This type of expression always returns a value of FALSE.
• A prefix for a compound expression. For example, the prefix
HTTP.REQ.HOSTNAME is a complete expression that returns a host name, and
HTTP.REQ.URL is a complete expression that returns a URL. The prefix
could also be used in conjuction with operations and additional prefixes to
form a compound expression.
Operations
In most expressions, you specify an operation on the data that the prefix
identifies. For example, suppose that you specify the following prefix:
http.req.url
Permitted Types of Expression Prefixes in Various NetScaler Feature
Feature Types of Expression Prefix Used in the Feature
DNS SYS, CLIENT, SERVER
Responder in Protection
Features HTTP, SYS, CLIENT
Content Switching HTTP, SYS, CLIENT
Rewrite HTTP, SYS, CLIENT, SERVER, URL, TEXT,
TARGET, VPN
Integrated Caching HTTP, SYS, CLIENT, SERVER
Access Gateway,
Clientless Access HTTP, SYS, CLIENT, SERVER, URL, TEXT,
TARGET, VPN