Specifications

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Cisco 1800 Series Integrated Services Routers (Fixed) Software Configuration Guide
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Chapter 8 Configuring a Simple Firewall
In the configuration example that follows, the firewall is applied to the outside WAN interface (FE0) on
the Cisco
1811 or Cisco 1812 and protects the Fast Ethernet LAN on FE2 by filtering and inspecting all
traffic entering the router on the Fast Ethernet WAN interface FE1. Note that in this example, the network
traffic originating from the corporate network, network address 10.1.1.0, is considered safe traffic and
is not filtered.
Configuration Tasks
Perform the following tasks to configure this network scenario:
• Configure Access Lists
• Configure Inspection Rules
• Apply Access Lists and Inspection Rules to Interfaces
An example showing the results of these configuration tasks is shown in the section “Configuration
Example.”
Note The procedures in this chapter assume that you have already configured basic router features as well as
PPPoE or PPPoA with NAT. If you have not performed these configurations tasks, see
Chapter 1, “Basic
Router Configuration,” Chapter 3, “Configuring PPP over Ethernet with NAT,” and Chapter 4,
“Configuring PPP over ATM with NAT,” as appropriate for your router. You may have also configured
DHCP, VLANs, and secure tunnels.
1 Multiple networked devices—Desktops, laptop PCs, switches
2 Fast Ethernet LAN interface (the inside interface for NAT)
3 PPPoE or PPPoA client and firewall implementation—Cisco 1811/1812 or Cisco 1801/1802/1803
series integrated services router, respectively
4 Point at which NAT occurs
5 Protected network
6 Unprotected network
7 Fast Ethernet or ATM WAN interface (the outside interface for NAT)