Using Regular Expressions in NPS

Article
07/03/2012

Applies To: Windows Server 2008

Using regular expressions in NPS

Network Policy Server (NPS) in Windows Server® 2008 supports the use of regular expressions for pattern matching. You can use this syntax to specify the conditions of network policy attributes and RADIUS realms.

Pattern-matching reference

You can use the following table as a reference source when creating regular expressions with pattern-matching syntax.

Character	Description	Example
\	Marks the next character as a character to match.	/n/ matches the character "n". The sequence /\n/ matches a line feed or newline character.
^	Matches the beginning of the input or line.
$	Matches the end of the input or line.
*	Matches the preceding character zero or more times.	/zo*/ matches either "z" or "zoo."
+	Matches the preceding character one or more times.	/zo+/ matches "zoo" but not "z."
?	Matches the preceding character zero or one times.	/a?ve?/ matches the "ve" in "never."
.	Matches any single character except a newline character.
(pattern)	Matches pattern and remembers the match. To match ( ) (parentheses), use "$" or "$".
x\|y	Matches either x or y.	/z\|food?/ matches "zoo" or "food."
{n}	Matches exactly n times (n is a nonnegative integer).	/o{2}/ does not match the "o" in "Bob," but matches the first two instances of the letter o in "foooood."
{n,}	Matches at least n times (n is a nonnegative integer).	/o{2,}/ does not match the "o" in "Bob" but matches all of the instances of the letter o in "foooood." /o{1,}/ is equivalent to /o+/.
{n,m}	Matches at least n and at most m times (m and nare nonnegative integers).	/o{1,3}/ matches the first three instances of the letter o in "fooooood."
[xyz]	Matches any one of the enclosed characters (a character set).	/[abc]/ matches the "a" in "plain."
[^xyz]	Matches any characters that are not enclosed (a negative character set).	/[^abc]/ matches the "p" in "plain."
\b	Matches a word boundary (for example, a space).	/ea*r\b/ matches the "er" in "never early."
\B	Matches a nonword boundary.	/ea*r\B/ matches the "ear" in "never early."
\d	Matches a digit character (equivalent to [0-9]).
\D	Matches a nondigit character (equivalent to [^0-9]).
\f	Matches a form feed character.
\n	Matches a line feed character.
\r	Matches a carriage return character.
\s	Matches any white space character including space, tab, and form feed (equivalent to [ \f\n\r\t\v]).
\S	Matches any non-white space character (equivalent to [^ \f\n\r\t\v]).
\t	Matches a tab character.
\v	Matches a vertical tab character.
\w	Matches any word character, including underscore (equivalent to [A-Za-z0-9_]).
\W	Matches any nonword character, excluding underscore (equivalent to [^A-Za-z0-9_]).
\num	Refers to remembered matches (?num, where num is a positive integer). For example, \1 replaces what is stored in the first remembered match. This option can be used only in the Replace text box when configuring attribute manipulation.
/n/	Allows the insertion of ASCII codes into regular expressions (?n, where n is an octal, hexadecimal, or decimal escape value).

Examples for network policy attributes

The following examples describe the use of the pattern-matching syntax to specify network policy attributes:

To specify all phone numbers within the 899 area code, the syntax is:

899.*
To specify a range of all IP addresses that begin with 192.168.1, the syntax is:

192\.168\.1\..+

Examples for manipulation of the realm name in the User Name attribute

The following examples describe the use of the pattern-matching syntax to manipulate realm names for the User Name attribute, which is located on the Attribute tab in the properties of a connection request policy.

To remove the realm portion of the User Name attribute

In an outsourced dial-up scenario in which an Internet service provider (ISP) routes connection requests to an organization NPS server, the ISP RADIUS proxy might require a realm name to route the authentication request. However, the NPS server might not recognize the realm name portion of the user name. Therefore, the realm name must be removed by the ISP RADIUS proxy before it is forwarded to the organization NPS server.
- Find: @microsoft\\.com
- Replace:
To replace user@example.microsoft.com with example.microsoft.com\user
- Find:(.*)@(.*)
- Replace:$2\$1
To replace domain\user with specific_domain\user
- Find:(.*)\\(.*)
- Replace: specific_domain\$2
To replace user with user@specific_domain
- Find:$
- Replace: @specific_domain

Example for RADIUS message forwarding by a proxy server

You can create routing rules that forward RADIUS messages with a specified realm name to a set of RADIUS servers when NPS is used as a RADIUS proxy. Following is a recommended syntax for routing requests based on realm name.

NetBIOS name	Pattern
WCOAST	^wcoast\\

In the following example, wcoast.microsoft.com is a unique user principal name (UPN) suffix for the DNS or Active Directory domain wcoast.microsoft.com. Using the supplied pattern, the NPS proxy can route messages based on domain NetBIOS name or UPN suffix.

NetBIOS name	UPN suffix	Pattern
WCOAST	wcoast.microsoft.com	^wcoast\\\|@wcoast\.microsoft\.com$

Ping user-name

Some RADIUS proxy servers and network access servers periodically send authentication and accounting requests (known as ping requests) to verify that the NPS server is present on the network. These ping requests include fictional user names. When NPS processes these requests, the event and accounting logs become filled with access reject records, making it more difficult to keep track of valid records.

When you configure a registry entry for ping user-name, NPS matches the registry entry value against the user name value in ping requests by other servers. A ping user-name registry entry specifies the fictional user name (or a user name pattern, with variables, that matches the fictional user name) sent by RADIUS proxy servers and network access servers. When NPS receives ping requests that match the ping user-name registry entry value, NPS rejects the authentication requests without processing the request. NPS does not record transactions involving the fictional user name in any log files, which makes the event log easier to interpret.

Note

Ping user-name is not installed by default. You must add ping user-name to the registry. You can add an entry to the registry using Registry Editor.

Warning

Incorrectly editing the registry might severely damage your system. Before making changes to the registry, you should back up any valued data on the computer.

Adding ping user-name to the registry

Ping user-name can be added to the following registry key as a string value by a member of the local Administrators group:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\IAS\Parameters

Name	Type	Data
ping user-name	REG_SZ	User name

Note

To indicate more than one user name for a ping user-name value, enter a name pattern, such as a DNS name, including wildcard characters, in Data.

Using Regular Expressions in NPS