Chapter 15 Firewall Mode Overview

Transparent Mode Overview

An Inside User Visits a Web Server Using NAT

Figure 15-8shows an inside user accessing an outside web server.

Figure 15-9 Inside to Outside with NAT

www.example.com

Internet

Static route on router to 209.165.201.0/27 through security appliance

Source Addr Translation

10.1.2.27209.165.201.10

 

10.1.2.1

Security

Management IP

appliance

10.1.2.2

Host

10.1.2.27

191243

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.

 

 

Cisco Security Appliance Command Line Configuration Guide

 

 

 

 

 

 

OL-12172-01

 

 

15-13

 

 

 

 

 

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Cisco Systems OL-12172-01 manual An Inside User Visits a Web Server Using NAT, 15-13
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OL-12172-01 specifications

Cisco Systems OL-12172-01 is a pivotal component in the landscape of networking and telecommunications, particularly catering to the needs of businesses seeking robust and efficient networking solutions. This particular offering is part of Cisco's ongoing commitment to providing advanced networking technologies that enhance connectivity, security, and overall operational efficiency.

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