Cisco ASA 5505 - Manual (Page 196)

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Cisco ASA 5500 Series Configuration Guide using the CLI
Chapter 4 Configuring the Transparent or Routed Firewall
Firewall Mode Examples
An Inside User Visits a Web Server
Figure 4-9 shows an inside user accessing an outside web server.
Figure 4-9 Inside to Outside
The following steps describe how data moves through the ASA (see Figure 4-9 ):
1. The user on the inside network requests a web page from www.example.com.
2. The ASA 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 ASA first classifies the packet according to a unique interface.
3. The ASA records that a session is established.
4. If the destination MAC address is in its table, the ASA 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 ASA table, the ASA attempts to discover the MAC
address by sending an ARP request or a ping. The first packet is dropped.
5. The web server responds to the request; because the session is already established, the packet
bypasses the many lookups associated with a new connection.
6. The ASA forwards the packet to the inside user.
Management IP
209.165.201.6
www.example.com
209.165.201.2
Host
209.165.201.3
Internet
92408