25-17
Cisco Security Appliance Command Line Configuration Guide
OL-12172-03
Chapter 25 Configuring Application Layer Protocol Inspection
DNS Inspection
•
real_ifc
—The name of the interface connected to the real addresses.
•
mapped_ifc
—The name of the interface where you want the addresses to be mapped.
•
mapped-address
—The translated IP address of the web server.
•
real-address
—The real IP address of the web server.
Step 2
Create an access list that permits traffic to the port that the web server listens to for HTTP requests.
hostname(config)#
access-list
acl-name
extended 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 mapped interface. To do so, use the
access-group
command,
as follows:
hostname(config)#
access-group
acl-name
in interface
mapped_ifc
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 Application Inspection” section on
page 25-5
.
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 security appliance for the scenario shown in
Figure 25-1
. It
assumes DNS inspection is already enabled.
hostname(config)#
static (inside,outside) 209.165.200.225 192.168.100.1 netmask
255.255.255.255 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
DNS Rewrite with Three NAT Zones
Figure 25-2
provides a more complex scenario to illustrate how DNS inspection allows NAT to operate
transparently with a DNS server with minimal configuration. For configuration instructions for scenarios
like this one, see the
“Configuring DNS Rewrite with Three NAT Zones” section on page 25-19
.
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Страница 45: ...P A R T 1 Getting Started and General Information ...
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Страница 277: ...P A R T 2 Configuring the Firewall ...
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Страница 561: ...P A R T 3 Configuring VPN ...
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