20-10
Cisco ASA 5500 Series Configuration Guide using ASDM
Chapter20 Configuring Objects
Configuring Regular Expressions

Guidelines and Limitations for Objects and Groups

This section includes the guidelines and limitations for this feature.
Context Mode Guidelines
Supported in single and multiple context mode.
Firewall Mode Guidelines
Supported in routed and transparent firewall modes.
IPv6 Guidelines
Supports IPv6, with limitations. (See the “Additional Guidelines and Limitations” section on
page 20-10.)
Additional Guidelines and Limitations
The following guidelines and limitations apply to object groups:
•Objects and object groups share the same name space.
•Object groups must have unique names. While you might want to create a network object group
named “Engineering” and a service object group named “Engineering,” you need to add an identifier
(or “tag”) to the end of at least one object group name to make it unique. For example, you can use
the names “Engineering_admins” and “Engineering_hosts” to make the object group names unique
and to aid in identification.
•You cannot remove an object group or make an object group empty if it is used in a command.
•The ASA does not support IPv6 nested object groups, so you cannot group an object with IPv6
entities under another IPv6 object group.
Configuring Regular Expressions
A regular expression matches text strings either literally as an exact string, or by using metacharacters
so that you can match multiple variants of a text string. You can use a regular expression to match the
content of certain application traffic; for example, you can match a URL string inside an HTTP packet.
This section describes how to create a regular expression and includes the following topics:
•Creating a Regular Expression, page20-10
•Building a Regular Expression, page20-12
•Testing a Regular Expression, page20-14
•Creating a Regular Expression Class Map, page20-14

Creating a Regular Expression

A regular expression matches text strings either literally as an exact string, or by using metacharacters
so you can match multiple variants of a text string. You can use a regular expression to match the content
of certain application traffic; for example, you can match a URL string inside an HTTP packet.