Cisco FirePOWER ASA 5500 series Configuration Manual page 439

Chapter 25 Configuring Application Layer Protocol Inspection
(Optional) Create one or more regular expression class maps to group regular expressions according to
Step 2
the "Creating a Regular Expression Class Map" section on page
(Optional) Create a DNS inspection class map by performing the following steps.
Step 3
A class map groups multiple traffic matches. Traffic must match all of the match commands to match
the class map. You can alternatively identify match commands directly in the policy map. The
difference between creating a class map and defining the traffic match directly in the inspection policy
map is that the class map lets you create more complex match criteria, and you can reuse class maps.
To specify traffic that should not match the class map, use the match not command. For example, if the
match not command specifies the string "example.com," then any traffic that includes "example.com"
does not match the class map.
For the traffic that you identify in this class map, you can specify actions such as drop, drop-connection,
reset, mask, set the rate limit, and/or log the connection in the inspection policy map.
If you want to perform different actions for each match command, you should identify the traffic
directly in the policy map.
a. Create the class map by entering the following command:
hostname(config)# class-map type inspect dns [match-all] class_map_name
hostname(config-cmap)#
Where class_map_name is the name of the class map. The match-all keyword specifies that traffic
must match all criteria to match the class map. match-all is the default and only option. The CLI
enters class-map configuration mode, where you can enter one or more match commands.
(Optional) To add a description to the class map, enter the following command:
b.
hostname(config-cmap)# description string
(Optional) To match a specific flag that is set in the DNS header, enter the following command:
c.
hostname(config-cmap)# match [not] header-flag [eq] {f_well_known | f_value}
Where the f_well_known argument is the DNS flag bit. The f_value argument is the 16-bit value in
hex. The eq keyword specifies an exact match.
(Optional) To match a DNS type, including Query type and RR type, enter the following command:
d.
hostname(config-cmap)# match [not] dns-type {eq t_well_known | t_val} {range t_val1
t_val2}
Where the t_well_known argument is the DNS flag bit. The t_val arguments are arbitrary values in
the DNS type field (0-65535). The range keyword specifies a range and the eq keyword specifies
an exact match.
(Optional) To match a DNS class, enter the following command:
e.
hostname(config-cmap)# match [not] dns-class {eq c_well_known | c_val} {range c_val1
c_val2}
Where the c_well_known argument is the DNS class. The c_val arguments are arbitrary values in
the DNS class field. The range keyword specifies a range and the eq keyword specifies an exact
match.
f. (Optional) To match a DNS question or resource record, enter the following command:
hostname(config-cmap)# match {question | {resource-record answer | authority | any}}
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