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22-24
Catalyst 6500 Series Switch and Cisco 7600 Series Router Firewall Services Module Configuration Guide using ASDM
OL-20748-01
Chapter 22 Applying Application Layer Protocol Inspection
DNS Inspection
hostname(config)#
access-list
acl-name
permit tcp any host
mapped-address
eq
port
where the arguments are as follows:
acl-name
—The name you give the access-list.
mapped-address
—The translated IP address of the web server.
port
—The TCP port that the web server listens to for HTTP requests.
Step 3
Apply the access list created in
Step 2
to the outside interface. To do so, use the
access-group
command,
as follows:
hostname(config)#
access-group
acl-name
in interface
outside
Step 4
If DNS inspection is disabled or if you want to change the maximum DNS packet length, configure DNS
inspection. DNS application inspection is enabled by default with a maximum DNS packet length of 512
bytes. For configuration instructions, see the
“Configuring DNS Inspection” section on page 22-24
.
Step 5
On the public DNS server, add an A-record for the web server, such as:
domain-qualified-hostname
. IN A
mapped-address
where
domain-qualified-hostname
is the hostname with a domain suffix, as in server.example.com. The
period after the hostname is important.
mapped-address
is the translated IP address of the web server.
The following example configures the FWSM for the scenario shown in
Figure 22-5
. It assumes DNS
inspection is already enabled.
Example 22-3 DNS Rewrite with Three NAT Zones
hostname(config)#
static (dmz,outside) 209.165.200.225 192.168.100.10 dns
hostname(config)#
access-list 101 permit tcp any host 209.165.200.225 eq www
hostname(config)#
access-group 101 in interface outside
This configuration requires the following A-record on the DNS server:
server.example.com. IN A 209.165.200.225
Configuring DNS Inspection
DNS inspection is enabled by default.
To enable DNS inspection (if it has been previously disabled) or to change the default port used for
receiving DNS traffic, perform the following steps:
Step 1
Create a class map or modify an existing class map to identify DNS traffic. Use the
class-map
command
to do so, as follows.
hostname(config)#
class-map
class_map_name
hostname(config-cmap)#
where
class_map_name
is the name of the traffic class. When you enter the
class-map
command, the
CLI enters class map configuration mode.
Step 2
Use the
match port
command to identify DNS traffic. The default port for DNS is UDP port 53.
hostname(config-cmap)#
match port udp eq 53
Содержание 6500 - Catalyst Series 10 Gigabit EN Interface Module Expansion
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Страница 297: ...P A R T 2 Configuring the Security Policy ...
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Страница 521: ...P A R T 3 System Administration ...
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