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Cisco ASA Series Firewall ASDM Configuration Guide
Chapter11 Configuring Inspection of Basic Internet Protocols
DNS Inspection
To use one of the preset security levels (Low, Medium, or High), drag the Security Level knob, then
click OK to add the inspection policy map. You can skip the rest of this procedure.
To customize each parameter and/or to configure packet matching inspection, click Details.
Detailed Steps—Protocol Conformance
Step1 Configure the following Protocol Conformance parameters:
Step2 Enable DNS guard function—Enables DNS Guard. The ASA tears down the DNS session associated
with a DNS query as soon as the DNS reply is forwarded by the ASA. The ASA also monitors the
message exchange to ensure that the ID of the DNS reply matches the ID of the DNS query.
Step3 Enable NAT re-write function—Translates the DNS record based on the NAT configuration.
Step4 Enable protocol enforcement—Enables DNS message format check, including domain name length of
no more than 255 characters, label length of 63 characters, compression, and looped pointer check.
Step5 Randomize the DNS identifier for DNS query—Randomizes the DNS identifier for a DNS query.
Step6 Enforce TSIG resource record to be present in DNS message—Requires a TSIG resource record to
be present. Actions include:
Action: Drop packet or Log—Drop or log a non-conforming packet.
Log: Enable or Disable—If you selected Drop packet, you can also enable logging.