Cisco Cisco Web Security Appliance S190 Guía Del Usuario
16-29
Cisco IronPort AsyncOS 7.0 for Web User Guide
OL-23079-01
Chapter 16 URL Filters
Regular Expressions
•
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
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
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
Note
Regular expressions that perform extensive character matching consume
resources and can affect system performance. For this reason, regular expressions
should be cautiously applied.
resources and can affect system performance. For this reason, regular expressions
should be cautiously applied.
Forming Regular Expressions
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:
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 “.*”.
higher CPU usage on the Web Security appliance. A redundant regular expression
is one that starts or ends with “.*”.