Cisco Cisco Web Security Appliance S170 사용자 가이드

Technically, AsyncOS for Web uses the Flex regular expression analyzer. For more detailed information 
about how it reads regular expressions, see http://flex.sourceforge.net/manual/Patterns.html.

You can use regular expressions in the following locations:

Custom URL categories for Access Policies. When you create a custom URL category to use with 
Access Policy groups, you can use regular expressions to specify multiple web servers that match 
the pattern you enter. For more information about creating custom URL categories, see 

.

Custom user agents to block. When you edit the applications to block for an Access Policy group, 
you can use regular expressions to enter specific user agents to block, such as Skype or Microsoft 
Internet Explorer. For more information about using regular expressions to block user agents, see 

Regular expressions that perform extensive character matching consume resources and can affect system 
performance. For this reason, regular expressions should be cautiously applied. 

Regular expressions are rules that typically use the word “matches” in the expression. They can be 
applied to match specific URL destinations or web servers. For example, the following regular 
expression matches any pattern containing blocksite.com:

\.blocksite\.com

 

Consider the following regular expression example: 

server[0-9]\.example\.com

 

In this example, server[

0-9

] matches 

server0

, 

server1

, 

server2

, ..., 

server9

 in the domain 

example.com

.

In the following example, the regular expression matches files ending in 

.exe

, 

.zip

, and .

bin

 in the 

downloads

 directory.

/downloads/.*\.(exe|zip|bin)

Avoid using regular expressions strings that are redundant because they can cause higher CPU usage on 
the Web Security appliance. A redundant regular expression is one that starts or ends with “.*”. 

You must enclose regular expressions that contain blank spaces or non-alphanumeric characters in 
ASCII quotation marks.