Filter
Top Products
15-13
Cisco Security Appliance Command Line Configuration Guide
OL-12172-01
Chapter 15 Firewall Mode Overview
Transparent Mode Overview
An Inside User Visits a Web Server Using NAT
Figure 15-8 shows an inside user accessing an outside web server.
Figure 15-9 Inside to Outside with NAT
The following steps describe how data moves through the security appliance (see Figure 15-8):
1. The user on the inside network requests a web page from www.example.com.
2. The security appliance 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 security appliance first classifies the packet according to a unique
interface.
3. The security appliance 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 security appliance.
4. The security appliance then records that a session is established and forwards the packet from the
outside interface.
5. If the destination MAC address is in its table, the security appliance forwards the packet out of the
outside interface. The destination MAC address is that of the upstream router, 209.165.201.2.
If the destination MAC address is not in the security appliance table, the security appliance attempts
to discover the MAC address by sending an ARP request and a ping. The first packet is dropped.
6. The web server responds to the request; because the session is already established, the packet
bypasses the many lookups associated with a new connection.
Management IP
10.1.2.2
www.example.com
10.1.2.1
Host
10.1.2.27
Internet
Source Addr Translation
209.165.201.1010.1.2.27
Static route on router
to 209.165.201.0/27
through security appliance
191243
Security
appliance