Cisco ASA 5505 - Manual (Page 884)

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Cisco ASA 5500 Series Configuration Guide using the CLI
Chapter 43 Configuring Inspection of Basic Internet Protocols
DNS Inspection
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 | match-any] class_map_name
hostname(config-cmap)#
Where class_map_name is the name of the class map. The match-all keyword is the default, and
specifies that traffic must match all criteria to match the class map. The match-any keyword
specifies that the traffic matches the class map if it matches at least one of the criteria. The CLI
enters class-map configuration mode, where you can enter one or more match commands.
b. (Optional) To add a description to the class map, enter the following command:
hostname(config-cmap)# description string
c. (Optional) To match a specific flag that is set in the DNS header, enter the following command:
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.
d. (Optional) To match a DNS type, including Query type and RR type, enter the following command:
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.
e. (Optional) To match a DNS class, enter the following command:
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}}
Where the question keyword specifies the question portion of a DNS message. The
resource-record keyword specifies the resource record portion of a DNS message. The answer
keyword specifies the Answer RR section. The authority keyword specifies the Authority RR
section. The additional keyword specifies the Additional RR section.
g. (Optional) To match a DNS message domain name list, enter the following command:
hostname(config-cmap)# match [not] domain-name {regex regex_id | regex class class_id]
The regex regex_name argument is the regular expression you created in Step 1 . The class
regex_class_name is the regular expression class map you created in Step 2 .
Step 4 Create a DNS inspection policy map, enter the following command:
hostname(config)# policy-map type inspect dns policy_map_name
hostname(config-pmap)#