Cisco Catalyst 6500 Series Configuration Manual page 158

Chapter 9 Configuring Network Address Translation
NAT Overview
When an inside host sends a DNS request for the address of ftp.cisco.com, the DNS server replies with
the global address (209.165.201.10). The FWSM refers to the static statement for the inside server and
translates the address inside the DNS reply to 10.1.3.14. If you do not enable DNS reply modification,
then the inside host attempts to send traffic to 209.165.201.10 instead of accessing ftp.cisco.com
directly.
Figure 9-6 DNS Reply Modification
DNS Server
2
1
DNS Query
Static Translation
Outside
ftp.cisco.com?
10.1.3.14 209.165.201.10
3
DNS Reply
FWSM
209.165.201.10
4
DNS Reply Modification
209.165.201.10 10.1.3.14
Inside
5
DNS Reply
10.1.3.14
User ftp.cisco.com
10.1.3.14
6
FTP Request
10.1.3.14
See the following command for this example:
FWSM/contexta(config)# static (inside,outside) 209.165.201.10 10.1.3.14 netmask
255.255.255.255 dns
Catalyst 6500 Series Switch and Cisco 7600 Series Router Firewall Services Module Configuration Guide
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