An Inside User Visits A Web Server Using Nat - Cisco 7604 Configuration Manual

Transparent Mode Overview

An Inside User Visits a Web Server Using NAT

Figure 5-9
Figure 5-10
209.165.201.0/27 through FWSM
The following steps describe how data moves through the FWSM (see
1.
2.
3.
4.
5.
6.
7.
Catalyst 6500 Series Switch and Cisco 7600 Series Router Firewall Services Module Configuration Guide using ASDM
5-14
shows an inside user accessing an outside web server.
Inside to Outside with NAT
www.example.com
Static route on router to
FWSM
The user on the inside network requests a web page from www.example.com.
The FWSM receives the packet and adds the source MAC address to the MAC address table, if
required. Because it is a new session, it verifies that the packet is allowed according to the terms of
the security policy (access lists, filters, AAA).
For multiple context mode, the FWSM first classifies the packet according to a unique interface.
The FWSM translates the real address (10.1.2.27) to the mapped address 209.165.201.10.
Because the mapped address is not on the same network as the outside interface, then be sure the
upstream router has a static route to the mapped network that points to the FWSM.
The FWSM then records that a session is established and forwards the packet from the outside
interface.
If the destination MAC address is in its table, the FWSM forwards the packet out of the outside
interface. The destination MAC address is that of the upstream router, 10.1.2.1.
If the destination MAC address is not in the FWSM table, the FWSM attempts to discover the MAC
address by sending an ARP request and a ping. The first packet is dropped.
The web server responds to the request; because the session is already established, the packet
bypasses the many lookups associated with a new connection.
The FWSM performs NAT by translating the mapped address to the real address, 10.1.2.27.
Internet
Source Addr Translation
10.1.2.27
10.1.2.1
Management IP
10.1.2.2
Host
10.1.2.27
Chapter 5 Configuring the Firewall Mode
209.165.201.10
Figure 5-9):
OL-20748-01