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22-20
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
Configuring DNS Rewrite
You configure DNS Rewrite using the
alias
,
static
, or
nat
commands. The
alias
and
static
command can
be used interchangeably; however, we recommend using the
static
command for new deployments
because it is more precise and unambiguous. Also, DNS Rewrite is optional when using the
static
command.
This section describes how to use the
alias
and
static
commands to configure DNS Rewrite. It provides
configuration procedures for using the
static
command in a simple scenario and in a more complex
scenario. Using the
nat
command is similar to using the
static
command except that DNS Rewrite is
based on dynamic translation instead of a static mapping.
This section includes the following topics:
•
Using the Alias Command for DNS Rewrite, page 22-20
•
Using the Static Command for DNS Rewrite, page 22-20
•
Configuring DNS Rewrite with Two NAT Zones, page 22-21
•
DNS Rewrite with Three NAT Zones, page 22-22
•
Configuring DNS Rewrite with Three NAT Zones, page 22-23
For detailed syntax and additional functions for the
alias
,
nat
, and
static
command, see the appropriate
command page in the
Catalyst 6500 Series Switch and Cisco 7600 Series Router Firewall Services
Module Command Reference
.
Using the Alias Command for DNS Rewrite
The
alias
command causes the FWSM to translate addresses on an IP network residing on
any
interface
into addresses on another IP network connected through a different interface. The syntax for this
command is as follows.
hostname(config)#
alias (inside)
mapped-address real-address
The following example specifies that the real address (192.168.100.10) on any interface
except
the inside
interface will be translated to the mapped address (
209.165.200.225)
on the inside interface. Notice that
the location of 192.168.100.10 is not precisely defined.
hostname(config)#
alias (inside) 209.165.200.225 192.168.100.10
Note
If you use the
alias
command to configure DNS Rewrite, proxy ARP will be performed for the mapped
address. To prevent this, disable Proxy ARP by entering the
sysopt noproxyarp internal_interface
command after entering the
alias
command.
Using the Static Command for DNS Rewrite
The
static
command causes addresses on an IP network residing on a
specific
interface to be translated
into addresses on another IP network on a different interface. The syntax for this command is as follows.
hostname(config)#
static (inside,outside)
mapped-address real-address
dns
The following example specifies that the address 192.168.100.10 on the inside interface is translated into
209.165.201.5 on the outside interface:
hostname(config)#
static (inside,outside) 209.165.200.225 192.168.100.10 dns
Summary of Contents for 6500 - Catalyst Series 10 Gigabit EN Interface Module Expansion
Page 35: ...P A R T 1 Getting Started and General Information ...
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Page 297: ...P A R T 2 Configuring the Security Policy ...
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Page 521: ...P A R T 3 System Administration ...
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Page 613: ...P A R T 4 Reference ...
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