How to Configure Cisco PIX Firewall Part I How to Configure PIX Firewall. Abstract:
Please find below a step by step process to configure the PIX Firewall from scratch. A simple scenario is given here where you have a corporate network with a PIX Firewall connected to the Internet through the Outside Interface, Internal Network through the Inside interface and DMZ through the DMZ Network. This paper would assist you in a simple step by step, near complete configuration for a PIX Firewall running a midsized corporate network
The Outside Network is connected to the internet through a Internet Router. The Inside Network is connected to a switch to the Internal Clients or Inside Hosts. The DMZ network consists of two servers, the Web server and the WEB server. Note: An effort has been made to keep this paper as simple as possible for the newbies. Much theory is not covered as you have numerous sites on the internet from where you can read that stuff.. Referral Links are given from time to time for more detailed configuration from Cisco website for Reference purpose. A Simple Network Diagram
The first thing in configuration is getting connected to the pix firewall. You use the console cable to connect the cable to the console port of the pix firewall. The other end goes to the serial port of your computer. You can then use a terminal emulation software to get connected to the prompt. For Windows users, HyperTerminal is a good option. 1
The next step is booting the Firewall. When a non-configured PIX Firewall boots up, it prompts to preconfigure it through interactive prompts. If you press Enter to accept the default answer of yes, you are presented with a series of prompts that lead you through the basic configuration steps: Pre-configure PIX Firewall now through interactive prompts [yes]? Enable Password []: abc123 Clock (UTC) Year [2002]: Month [Aug]: Day [2]: 12 Time [2:45:37]: 12:22:00 Inside IP address: 10.1.1.1 Inside network mask: 255.255.255.0 255.255.255.0 Host name: pixfirewall Domain name: secmanager.com IP address of host running PIX Device Manager: 101.1.111 Use this configuration and write to flash? Y The above can also be achieved by entering the setup command in privileged mode. The pix Firewall has four modes of Operation as given below: • Unprivileged mode: This mode provides a restricted, limited, view of PIX Firewall settings. Example : pixfirewall> • Privileged mode: This mode enables you change the current firewall settings. Example: pixfirewall# • Configuration mode: This mode enables you to change the system configurations of the firewall. Example pixfirewall(config)# • Monitor mode: This mode is used to update the image over the network, perform password recovery or backup the configuration onto the TFTP server In case you don’t want to use the setup command for the configuration, you can use the console connection and configure as follows: Priveleged mode
The first step is to enter the privileged mode: Pixfirewall> en Password: (Enter or Cisco, for more information refer to the configuration manuals that came with the firewall) Pixfirewall# Changing password
The next step is to change the enable password on the firewall: Pixfirewall# enable password abc123 The next step is to enter the configuration mode for changing the system configurations. To enter the config mode, enter the following command: 2
Pixfirewall# configure terminal (or popularly conf t) Pixfirewall (config) # Give a Hostname to the firewall.
You might want to give a hostname to the firewall. You can use the hostname command to do this. Pixfirewall (config) #hostname CorpFW1 CorpFW1(config)# To save the information, use the write memory command or simply wr mem. CorpFW1(config)# write memory For purposes of this document, we continue to give the firewall the name “Pixfirewall”. So let us change the name back to Pixfirewall CorpFW1(config)# hostname Pixfirewall Pixfirewall (config) # wr mem Setup the console timeout:
Next, you might want to setup the console timeout for security reasons. The default timeout is 0, which means unlimited. Pixfirewall (config) # console timeout 5 This means you have setup a console timeout of 5 minutes ( the value can be set from 0-60 minutes) which means after a idle time of 5 minutes, the session will be closed. Setup a banner to your Pix firewall.
You can do this with the banner command: Pixfirewall (config) # banner exec Unauthorized access will be prosecuted. There are also two other commands available: banner login banner motd To remove banner you use the no banner or clear banner commands. Naming an Interface:
The first two interfaces would have the default names of inside and outside. While inside interface has a security level of 100, the outside interface has a default security level of 0. Let us configure the Ethernet 2 interface as the dmz. Pixfirewall (config) # nameif ethernet2 dmz sec60 In this example, we are assigning a security_level of 60 to the DMZ network. 3
Configure the Interface:
Now let us turn the interface on and configure the speeds for these interfaces: Pixfirewall (config) # interface ethernet0 100full Pixfirewall (config) #interface ethernet1 100full Pixfirewall (config) #interface ethernet2 100full Assign IP Address to the Interface:
Pixfirewall (config) # ip address outside 192.168.1.1 255.255.255.0 255.255.255.0 Pixfirewall (config) # ip address inside 10.1.1.1 255.255.255.0 Pixfirewall (config) #ip address dmz 172.16.16.1 255.255.255.0 255.255.255.0 You can use the “show ip” command to view the ip address information and “clear ip” command to remove all assigned IP addresses from all interfaces. Route Commands:
Now let us setup the routing information on the pix firewall. This is the default route, where we are configuring the next hop of the default route to the IP address of the Internet Router which is 192.168.1.100 192.168.1.100 Pixfirewall (config) # route outside 0.0.0.0 0.0.0.0 192.168.1.100 192.168.1.100 1 Pixfirewall (config) # route inside 10.0.0.0 255.0.0.0 10.1.1.1 1 Pixfirewall (config) # route dmz 172.16.17.0 255.255.255.0 255.255.255.0 172.16.16.1 1 So using these route commands you are telling the PIX router that route the traffic for 10.0.0.0/8 network to inside, 172.16.17.0/24 network to dmz. The default route is set for outside, which means for all other networks, route the traffic through the outside interface.
How to Configure Cisco PIX Firewall Part II Please find below a step by step process to configure the PIX Firewall from scratch. A simple scenario is given here where you have a corporate network with a PIX Firewall connected to the Internet through the Outside Interface, Internal Network through the Inside interface and DMZ through the DMZ Network. This paper would assist you in a simple step by step, near complete configuration for a PIX Firewall running a midsized corporate network This is part II of the How to Configure Pix Firewall, a step by step approach. This is in continuation of the Part I of the series. The Simple Network Diagram:
A Simple Network Diagram
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Network Address Translation:
Let us take a simple scenario to explain this section. Let us say that all the computers in the inside network want internet access. NAT also allows you to keep your internal IP hidden from the outside network. To achieve this you need to implement address translation. You do this using the “nat” and “global” commands. The NAT command:
Pixfirewall (config) # nat (inside) 1 0.0.0.0 0.0.0.0 In this example, the nat (inside) 1 10.0.0.0 255.255.255.0 command means that all outbound connections from a host within the specified network, 10.1.1.0, can pass through the PIX Firewall (with address translation). Global command:
Pixfirewall (config) #global (outside) 1 192.168.1.10-1 192.168.1.10-192.168.1.50 92.168.1.50 This means that use the IP address from 192.168.1.10 to 192.168.1.50 for NATing the traffic c oming from the inside interface. There is also another simple way for allowing internet /outside access to the inside network using PAT or port address translation. What this would do is hide all the internal networks behind the outside interface of the PIX firewall and transmit traffic using Port Address Translation. One limitation to this approach is that at a time it can process only less than 64000 client computers. But in most cases, this is more than enough. PAT using Global:
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Pixfirewall (config) # global (outside) 1 interface Now, let us configure the two servers in the dmz network, the webserver and the mailserver. The wish list is to allow traffic from anywhere to reach the webserver on http, https and ftp and traffic from anywhere to reach the mail server on the smtp port. To do this we need to setup statics and access-lists. Setting up Static’s:
Pixfirewall (config) #static (dmz,outside) 192.168.1.2 172.16.16.2 netmask 255.255.255.255 0 0 Pixfirewall (config) # static (dmz,outside) 192.168.1.4 172.16.16.4 netmask 255.255.255.255 255.255.255.255 0 0 Having configured the statics, now let us move on to configure the object-groups that would be used in configuring the access-list Configuring object-groups:
Pixfirewall (config) #object-group service webservices tcp Pixfirewall (config-service) # port-object eq http Pixfirewall (config-service) # port-object eq https Pixfirewall (config-service) # port-object eq ftp Pixfirewall (config-service) # exit Pixfirewall (config) # Now let us configure the access-lists to allow access to the dmz networks from outside and also to the other interfaces: Configuring Access-list:
Pixfirewall (config) # access-list external permit tcp any host 192.168.1.2 object-group webservices Pixfirewall (config) # access-list external permit tcp any host 192.168.1.4 eq smtp. Pixfirewall (config) #access-list external deny ip any any (This is a any any drop rule. Place this at the end of the access-lists. This acl won’t allow any other traffic that is not explicitly allowed to get into the firewall. This is often helpful in checking the number of hits on this acl from outside for troubleshooting or analysis purposes.) Pixfirewall (config) #access-list internal permit ip 172.16.16.0 255.255.255.0 10.1.1.0 255.255.255.0 255.255.255.0 Pixfirewall (config) # access-list internal deny ip any any Pixfirewall (config) # access-list dmz permit ip 10.1.1.0 255.255.255.0 255.255.255.0 172.16.16.0 255.255.255.0 255.255.255.0 Pixfirewall (config) #access-list dmz deny ip any any Now map these access-lists to access-groups for these access-lists to work properly: Configuring Access Groups:
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Pixfirewall (config) #access-group external in interface outside Pixfirewall (config) # access-group internal in interface inside Pixfirewall (config) #access-group dmz in interface ethernet2 With this we have configured the PIX firewall for a normal office setup. These commands will be helpful in checking the configuration of the pix firewall and also in troubleshooting, analysis and fine tuning. Useful Commands:
show config show blocks show checksum show conn show cpu usage show history show memory show processes show routing show running-config show startup-config show tech-support show tcpstat show traffic show uauth/clear uauth show version show xlate/clear xlate
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