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Barracuda Load Balancer ADC

Extended Match and Condition Expressions

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You use extended match and condition expressions in content rules, HTTP request rewrite rules, and HTTP response rewrite rules to match the requests and responses that you want to be handled by these rules.

Quick Reference

Expressions
  • Element Match
  • (Expression) [Join (Expression) ...]
Joins
  • &&, ||
Elements
  • Request Elements: Method, HTTP-Version, Client-IP, URI, URI-Path, Header
  • Request Parameters: Parameter, Pathinfo
  • Response Elements: Status-code, Response-Header
Operators
  • Matching: eq, neq, req, nreq
  • Containing: co, nco, rco, nrco
  • Existence: ex, nex

Structure

An expression consists of one or more element matches that are combined with join operators to indicate AND and OR operations to combine the element matches. Use parentheses to delimit individual element matches when using join operators. You can nest parentheses.

An element match consists of an element, an optional element name, and an operator followed by an optional value. Some elements like Header require an element name like User-Agent, whereas some elements like HTTP-Version require no further qualification. Also, some operators like eq (stands for equals) require a value, whereas some operators like ex (stands for exists) require no value.

Tokens are delimited by space and the parenthesis characters. You can use double quotes (") to enclose single tokens which contain parenthesis characters or spaces. Use the backslash (\) to escape, or remove the special meaning of the special characters (space and parentheses).

Operators

You can use the following operators in an element match. The operators are case-insensitive; for example, eq, Eq, and EQ are all treated the same.

OperatorDescription
eqTrue if the operand is equal to the given value. A case-insensitive string comparison is performed. Thus, a value of 01 is not the same as a value of 1, whereas one and ONE are treated the same.
neqTrue if the operand is not equal to the given value. A case-insensitive string comparison is performed.
coTrue if the operand contains the given value.
ncoTrue if the operand does not contain the given value.
rcoTrue if the operand contains the given value, which is treated as a regular expression.
nrcoTrue if the operand does not contain the given value, which is treated as a regular expression.
reqTrue if the operand matches the given value, which is treated as a regular expression.
nreqTrue if the operand does not match the given value, which is treated as a regular expression.
exTrue if the operand exists. A value is not required.
nexTrue if the operand does not exist. A value is not required.

Elements

The elements listed in the following table can only be used in certain expressions. Elements and element names are case-insensitive; for example, Method and METHOD are treated the same.

ElementDescriptionRestrictions
Method

The HTTP method that was received in the request.

Example: (Method eq GET)

Only allowed in:

  • Extended match expressions
  • Request rewrite conditions
HTTP-Version

The version of the HTTP protocol of the request.

Example: (HTTP-Version eq HTTP/1.1)

Only allowed in:

  • Extended match expressions
  • Request rewrite conditions
Header

An HTTP header in the request. An element name is required after the header.

Example: (Header Accept co gzip)

This example checks if the Accept header contains the string gzip.

Only allowed in:

  • Extended match expressions
  • Request rewrite conditions
  • Response rewrite conditions
Client-IP

The IP address of the client sending the request. The IP address can be either a host IP address or subnet IP address specified by a mask.

Only eq and neq operations are allowed for this element.

Examples: (client-ip eq 192.168.1.0/24), (Client-IP eq 192.168.1.10)

Only allowed in:

  • Extended match expressions
  • Request rewrite conditions
URI

The uniform resource identifier in the request. This includes any query parameters in the request.

Example: (URI rco /abc.*html?userid=b)

Only allowed in:

  • Extended match expressions
  • Request rewrite conditions
URI-path

The path portion of the URI, which excludes any query parameters.

Example: (URI-path req \/.*copy%20[^/]*)

Only allowed in:

  • Extended match expressions
Pathinfo

The portion of the URL which is interpreted as PATH_INFO on the server. The Barracuda Load Balancer ADC uses a set of known
extensions to determine whether a portion of the URL provides information about a file path.

For example, if the request URL is /twiki/view.cgi/Engineering, then /Engineering is considered to be the pathinfo rather than
part of the URL.

Example: (PathInfo rco abc*)

Only allowed in:

  • Extended match expressions
  • Request rewrite conditions
Parameter

A parameter in the query string part of the URL and serves as a name-value pair. The special $NONAME_PARAM
parameter is used when the parameter name is absent.

Examples: (Parameter sid eq 1234), (Parameter $NONAME_PARAM co abcd)

Only allowed in:

  • Extended match expressions
  • Request rewrite conditions
Status-code

The status code of the response returned by the servers.

Example: (status-code eq 302)

Only allowed in response rewrite conditions.
Response-header

The HTTP response header in the response. The Response-header term must be followed by the name of the header on which the
action is to be applied.

Example: (Response-Header Set-Cookie co sessionid)

Only allowed in response rewrite conditions.

Combining Expressions

You can use the following join operators to combine expressions:

OperatorDescription
||True if either of the expressions are true.
&&True only if both the expressions are true.

When you combine element matches, you must enclose each element in parentheses. Combining element matches without parentheses is not allowed.

Example: (Header cookie ex) && (URI rco .*\.html) && (Method eq GET)

Nesting Expressions

You can next sub-expressions by enclosing parentheses within expressions. This makes the expression more readable and clear.

Example: (HTTP-Version eq HTTP/1.1) && ((Header Host eq www.example.com) || (Header Host eq website.example.com))

Escaping

Escape special characters by enclosing entire values in double quotes (") or prefixing characters with a backslash (\). The backslash character escapes all characters, not just the special characters. For example, \c stands for the character c. In other words, the backslash followed by any character stands for the character, whether or not that character has a special meaning in the syntax.

The space character and the parentheses characters are special characters because they cause the parser to split the string into tokens at these separators. In some cases, it is required to specify these characters as part of the value itself. For example, the User-Agent header typically contains both spaces and parentheses, as in:

User-Agent: Mozilla/5.0 (Linux i686; en-US; rv:1.8.1.3) Firefox/2.0.0.3

When you write expressions or conditions to match the header example above, you can escape the special characters as follows:

  • Header User-Agent eq “Mozilla/5.0 (Linux i686; en-US; rv:1.8.1.3) Firefox/2.0.0.3”
  • Header User-Agent eq Mozilla/5.0\ \(Linux\ i686;\ en-US;\ rv:1.8.1.3\)\ Firefox/2.0.0.3

To specify the double-quote character itself, it must be escaped with a back-slash. This is true inside a quoted string, or a non-quoted string. Note that the single quote character has no special meaning, and is treated as any other character.

To specify the back-slash character itself, it must be escaped as \\. This is true within both quoted strings and non-quoted strings.

Macro Definitions

The Barracuda Load Balancer ADC supports several macros to assist in configuring policies. The following table describes these macros arranged by the areas where they can be used. The URI in these cases does not include the host.

MacroDescription
$SRC_ADDR Inserts the source (client) IP address. You can use it for the new value (Rewrite Value parameter) when inserting or rewriting a header.
$URISpecifies the complete request URI including the query string. If you are rewriting or redirecting the URI, use this macro in the new value.
$AUTH_USERAdds the username. (1) (2) (3)
$AUTH_PASSWDAdds the password. (1) (2) (3)
$AUTH_GROUPS

Adds the user roles. (1) (2) (3)

URL ACLs
$NONAME_PARAMInserts a parameter with no name (see No Name Parameters)

Notes:

(1) The URL is not protected. Access control or authentication is disabled. The value substituted for the macro is the special string NCURLNotProtected.
(2) The client has not logged in. The value substituted for the macros is the special string NCNoUserSession.
(3) The user does not belong to any groups. The value substituted for $AUTH_GROUPS is the special string NCNOUserRoles.

No Name Parameters

There might be times when you want to configure a parameter without a name. For example, consider a site that displays a pop-up window to visitors. A Javascript adds a query string that results in the following GET request:

GET /ad?xyz

The Barracuda Load Balancer ADC does not learn “no name” parameters such as query strings like "GET /ad?0" added by a Javascript. As a workaround: add a null value URL ACL.

The Barracuda Load Balancer ADC treats xyz as the value of a parameter. In this case, you cannot create an exception rule based on the xyz value because there is no way to associate it with a named parameter.

To address such situations (that is, requests with parameter name-value pairs of the type ?xyz or ?=xyz where xyz is the value), you can use a special token: $NONAME_PARAM (case-insensitive). This token lets you create an expression for a parameter without a name, as in the following examples:

set = parameter $NONAME_PARAM ex

set = parameter $NONAME_PARAM eq 0

set = parameter $noname_param co xyz

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