Suggested prerequisite reading:
»Cisco Forum FAQ »Router configuration to run server (with and without port forwarding)
»Cisco Forum FAQ »PIX Firewall/ASA configuration to run server (with and without port forwarding)
Introduction
Following the same concept of just having single Internet gateway, there is typically NAT/PAT consideration. As mentioned on the reading above, you must use Internet-routable (Public) IP address to go out to the Internet. Therefore there should be NAT/PAT process that translate Private IP address into Public IP address.
Since in this case there are two devices (router and ASA or PIX firewall), you must choose to use one to do such NAT/PAT process. Typically you want to have the ASA or PIX firewall to do the NAT/PAT process, especially when you do have the ASA or PIX firewall facing the Internet (ISP) directly.
In addition, there must be proper IP routing in place between devices and subnets. This way; the ISP, ASA or PIX firewall, router, and LAN users know how to reach each other and other subnets. For simple network, static routes as shown in the sample configuration should suffice.
As noted, the above links are suggested prerequisite reading since this sample configuration presents the next chapter of the prerequisite reading. In addition, you must have a familiarity of both older PIX OS commands and newer PIX/ASA OS commands; or at least familiar enough with the older PIX OS commands to configure PIX/ASA running newer OS commands. If you are new to CLI specifically for router, PIX, and ASA; then check out the following FAQ for info.
»Cisco Forum FAQ »The most straight-forward way to configure Cisco router: Introduction to CLI
»Cisco Forum FAQ »Straight-forward way to configure Cisco PIX Firewall/ASA: Introduction to CLI
Consideration
Typical network environment that might utilize following sample PIX configuration is as follows
* There is a modem in front of the PIX, which the modem connects to the ISP
* ISP is providing Public IP address to the PIX statically
* There is NAT/PAT in place on the PIX to translate internal IP addresses to the ISP-provided Public IP address
* The router behind the PIX is directly connected physically to the PIX LAN (inside) interface using crossover patch cable
* No devices (workstations, servers, switches, hubs) are sitting between the PIX and the router
* All the switches, workstations, and servers are sitting behind the router
* The router is acting as DHCP server, which provide dynamic IP info for hosts behind the router
* The router is not able to provide stateful firewall protection; hence PIX is setup in front of the router before connecting to the ISP (the modem) to protect your LAN from unauthorized accesses
This sample configuration assumes the followings:
* You receive a static IP address from ISP as 1.1.1.2
* The ISP default gateway is 1.1.1.1
* You are running servers visible to the public
* The servers are web, mail, and ftp
* Your internal webserver IP address is 192.168.100.1
* Your internal ftp server IP address is 192.168.100.2
* Your internal mail server IP address is 192.168.100.3
* You have syslog server with IP address of 192.168.100.5
* You use 1.1.1.2 (the PIX outside interface IP address) to be your three server's public IP address (static PAT)
* You permit only internal host of 192.168.100.4 to telnet and to pdm to the PIX
* Internal hosts are receiving IP address automatically (as DHCP clients) from the router
* Since the PIX inside interface subnet is /30, there would be no other IP-based hosts between the PIX and the router within the same subnet
PIX Configuration
Router Configuration
Note:
* The PIX Firewall Inside and Router FastEthernet0 interfaces are within 10.0.0.0/30 network. This means there are no other devices within such network beside the PIX and the router. Sometimes there are other machines within this network where the PIX Inside and Router FastEthernet0 interfaces connect to a switch using straight-through cables. Other machines such as servers connect to the same switch. Since there are more devices, then typically the network is /24 size or larger (i.e. 10.0.0.0/24).
When this is the case, make sure that all of those machines have default gateway of 10.0.0.2 (the Router FastEthernet0 interface IP address) and not the 10.0.0.1 (the PIX Firewall Inside interface IP address). This way all the machines have ability to reach both any machines within 192.168.100.0/24 (the Inside LAN) and the Internet.
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by aryoba 
last modified: 2009-07-27 13:24:43 |
