Cisco 7604 Configuration Guide - Page 120
An Inside User Visits a Web Server Using NAT, Inside to Outside with NAT
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Transparent Mode Overview Chapter 5 Configuring the Firewall Mode An Inside User Visits a Web Server Using NAT Figure 5-9 shows an inside user accessing an outside web server. Figure 5-10 Inside to Outside with NAT www.example.com Internet Static route on router to 209.165.201.0/27 through FWSM FWSM 10.1.2.1 Source Addr Translation 10.1.2.27 209.165.201.10 Management IP 10.1.2.2 190153 Host 10.1.2.27 The following steps describe how data moves through the FWSM (see Figure 5-9): 1. The user on the inside network requests a web page from www.example.com. 2. 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. 3. 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. 4. The FWSM 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 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. 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. 7. The FWSM performs NAT by translating the mapped address to the real address, 10.1.2.27. 5-14 Catalyst 6500 Series Switch and Cisco 7600 Series Router Firewall Services Module Configuration Guide using ASDM OL-20748-01
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