Before using this chapter, be sure that you have planned your site's security policy, as described in "Introduction," and configured the PIX Firewall, as described in "Configuring the PIX Firewall." Acronyms in the text are defined in "Acronyms and Abbreviations."
This chapter provides network diagrams and the configuration instructions to create them. Further information about the commands in the configurations can be found in "Command Reference."
If you are starting a configuration, you may want to use the forms provided in "Configuration Forms," to help you plan a configuration.
 | Note For IPSec example configurations, refer to the IPSec User Guide for the Cisco Secure PIX Firewall Version 5.2. |
This chapter includes the following sections:
- Two Interfaces without NAT - Basic
- Two Interfaces with NAT - Basic
- Two Interfaces with NAT - Advanced
- Three Interfaces without NAT
- Three Interfaces with NAT
- Four Interfaces with NAT
- Six Interfaces with NAT
- Failover Configuration
Note The PIX 506 supports only two interfaces.
Two Interfaces without NAT - Basic
When you first add a PIX Firewall to an existing network, it is easiest to implement its use if you do not have to renumber all the inside and outside IP addresses. The configuration in Figure 4-1 illustrates this scenario. Syslog is enabled to facilitate troubleshooting. All inside hosts can start connections. All external hosts are blocked from initiating connections or sessions on inside hosts. If you use Inter-NIC registered IP addresses, only use those addresses that you own.
Figure 4-1: Two Interfaces without NAT
Table 4-1 lists the configuration.
Table 4-1: Two Interfaces without NAT
| Configuration | Description |
|---|---|
nameif ethernet0 outside security0 | PIX Firewall provides nameif and interface command statements for the interfaces in the default configuration. Change the default auto option in the interface command to the specific line speed for the interface card. |
ip address outside 209.165.201.3 | Identify the IP addresses for both interfaces. |
hostname pixfirewall | Specifies the host name for the PIX Firewall. This name appears in the command line prompt. |
arp timeout 14400 | Sets the ARP timeout to 14,400 seconds (four hours). Entries are kept in the ARP table for four hours before they are flushed. Four hours is the standard default value for ARP timeouts. |
no failover | Disables failover access. |
names | Enables use of text strings instead of IP addresses. This makes your configuration files more readable. |
pager lines 24 | Enables paging so that if when 24 lines of information display, PIX Firewall pauses the listing and prompts you to continue. |
logging buffered debugging | Enables syslog messages, which provide diagnostic information and status for the PIX Firewall. PIX Firewall makes it easy to view syslog messages with the show logging command. |
nat (inside) 0 172.31.2.0 255.255.255.0 | Lets inside IP addresses be recognized on the outside network and lets inside users start outbound connections. |
rip inside default | Sets RIP listening attributes. The first command causes the PIX Firewall to broadcast a default route on the inside interface. Broadcasting a default route sends network traffic to the PIX Firewall if your internal network is running RIP. The next command disables passive RIP listening on the inside. The next command disables broadcasting a default route on the outside. This is desirable when the network is attached to the Internet, but not when on an intranet. The last command disables passive RIP listening on the outside. |
route outside 0.0.0.0 0.0.0.0 209.165.201.1 1 | Sets the outside default route to the router attached to the Internet. |
timeout xlate 3:00:00 | Default values for the maximum duration that PIX Firewall resources can remain idle until being freed. Additional users cannot make connections until a connection resource is freed either by a user dropping a connection or by an xlate and conn timer time out. |
no snmp-server location | Specifies that SNMP information may be accessed by internal hosts that know the community string, but PIX Firewall does not send trap information to any host. |
mtu outside 1500 | Sets the maximum transmission unit value for Ethernet access. |
Two Interfaces with NAT - Basic
In Figure 4-2, the PIX Firewall has two interfaces. In this configuration, there is no user authentication, no authorization, and no syslog or SNMP logging of troubleshooting messages. All inside users can start outbound connections and all connections from the outside are dropped. A configuration such as this is a good example of the basic commands used to create a secured network.
Figure 4-2: Two Interfaces with NAT
Table 4-2 lists the configuration.
Table 4-2: Two Interfaces with NAT
| Configuration | Description |
|---|---|
nameif ethernet0 outside security0 | PIX Firewall provides nameif and interface command statements for the interfaces in the default configuration. Change the default auto option in the interface command to the specific line speed for the interface card. |
ip address outside 209.165.201.3 255.255.255.224 | Identify the IP addresses for both interfaces. |
arp timeout 14400 | Set the ARP timeout to 14,400 seconds (four hours). Entries are kept in the ARP table for four hours before they are flushed. |
nat (inside) 1 0 0 | Permit all inside users to start outbound connections using the translated IP addresses from the global pool. |
global (outside) 1 209.165.201.10-209.165.201.30 | Create a pool of global addresses that translated addresses use when they exit the firewall from the protected networks to the unprotected networks. The global command statement is associated with a nat command statement by the NAT ID, which in this example is 1. Because there are limited IP addresses in the pool, a PAT (Port Address Translation) global is added to handle overflow. |
no rip inside default | PIX Firewall does use RIP information for its forwarding decisions, but these commands can be useful for broadcasting a default route—if your network uses the RIP protocol. However, most do not. In most cases, you can ignore these command statements. |
route outside 0.0.0.0 0.0.0.0 209.165.201.1 1 | Sets the outside default route to the router attached to the Internet. |
timeout xlate 3:00:00 | Sets default values for the maximum duration that PIX Firewall resources can remain idle until being freed. Additional users cannot make connections until a connection resource is freed either by a user dropping a connection or by an xlate and conn timer time out. |
access-list acl_grp permit icmp any any | Allows inbound and outbound pings. |
no snmp-server location | Specifies that SNMP information may be accessed by internal hosts that know the community string, but PIX Firewall does not send trap information to any host. |
telnet 10.0.0.100 255.255.255.255 | Specifies that host 10.0.0.100 is permitted to access the PIX Firewall console via Telnet and that 15 minutes are allowed before the idle timer runs out and the session is logged off. |
mtu outside 1500 | Sets the maximum transmission unit value for Ethernet access. |
Two Interfaces with NAT - Advanced
The configuration in Figure 4-3 provides an overview of how the various commands are used to create a configuration.
This configuration shows the use of PAT (Port Address Translation), denying Java applets, using the AAA commands, creating a mail server, permitting NFS, initializing SNMP, and setting console access with Telnet.
Figure 4-3: Two Interfaces with NAT - Advanced
Table 4-3 lists the configuration.
Table 4-3: Two Interfaces with NAT - Advanced
| Configuration | Description |
|---|---|
nameif ethernet0 outside security0 | PIX Firewall provides nameif and interface command statements for the interfaces in the default configuration. Change the default auto option in the interface command to the specific line speed for the interface card. |
ip address inside 10.1.1.1 255.255.255.0 | Identify the IP addresses for both interfaces. |
logging on | The logging host command statement specifies which host runs a syslog server. This command also causes the PIX Firewall to start sending syslog messages to that host. The logging trap command statement sets syslog to send all possible messages to the syslog host. The no logging console command statement disables displaying messages to the console. |
arp timeout 600 | Set an ARP timeout to 600 seconds (10 minutes). Use this arp timeout command statement when you set up a network and change inside and outside host addresses often. |
nat (inside) 1 0.0.0.0 0.0.0.0 | Permit all inside users to start outbound connections using the translated IP addresses from the global pool. |
global (outside) 1 209.165.201.6-209.165.201.8 | Create pools of global addresses to let the nat command statements use the address pools for translating internal IP addresses to external addresses. Each pool is designated by the number from the nat command statement, in this case, 1 and 2. |
access-list acl_in permit icmp any any | Allow inbound and outbound pings. Access list group "acl_in" is bound to the inside interface and group "acl_out" is bound to the outside interface. |
access-list acl_in deny tcp host 192.168.3.3 any eq | Create outbound access lists to determine which hosts can access services. The first access-list command statement denies host 192.168.3.3 from accessing H.323 (port 1720) services such as MS NetMeeting or InternetPhone. The next command statement denies all hosts from accessing the Web (port 80). The next command statement permits host 192.168.3.3 to use the Web. The last access-list command statement permits host 10.1.1.11 access to the Web (at port 80). |
access-group acl_in interface inside | Specify that the access-list group regulates the activities of inside hosts starting outbound connections. |
filter java http 192.168.3.3 255.255.255.255 0 0 | Keep host 192.168.3.3 from downloading Java applets. |
no rip outside passive | The first command disables RIP listening on the outside interface. The second command disables broadcasting a default route on the outside. The third command enables RIP listening on the inside and the last command causes PIX Firewall to broadcast a default route on the inside interface. |
route outside 0 0 209.165.201.4 1 | Set the default route on the outside network to be 209.165.201.4. This is the IP address of the gateway host connecting to the Internet. |
aaa-server TACACS+ (inside) host 10.1.1.12 1q2w3e | The aaa-server command specifies the IP address of the TACACS+ authentication server. The aaa authentication command statement specifies that users on network 192.168.3.0 starting FTP, HTTP, and Web connections from the inside interface be prompted for their usernames and passwords before being permitted to access these servers on other interfaces. The aaa authorization command statement lets the users on 192.168.3.0 access FTP, HTTP, or Telnet, and any TCP connections to anywhere as authorized by the AAA server. Even though it appears that the aaa commands let the PIX Firewall set security policy, the authentication server actually does the work to decide which users are authenticated and what services they can access when authentication is permitted. |
static (inside, outside) 209.165.201.16 192.168.3.16 | The static command statement creates a net static command statement, which is a static command statement for a set of IP addresses, in this case for IP addresses 209.165.201.17 through 209.165.201.30. |
static (inside, outside) 209.165.201.11 10.1.1.11 | The static command statement with the access-list command statement establishes an externally visible IP address for Web access (port 80 in the access-list command statement). |
access-list acl_out permit udp host 209.165.201.2 | Refine the accessibility of the static command by permitting Sun RPC over the UDP portmapper on port 111 with the rpc literal. Refer to the UNIX /etc/rpc file and the UNIX rpc(3N) command page for more information. Once you create an access-list command statement for RPC, you can use the following command from outside host 209.165.201.2 to track down the activity of a PCNFSD on RPC 150001: |
access-list acl_out permit udp host 209.165.201.2 | |
static (inside, outside) 209.165.201.12 10.1.1.3 | Identify access to the 10.1.1.3 mail server through global address 209.165.201.12. The access-list command statement any outside host access to the static via SMTP (port 25). By default, PIX Firewall restricts all access to mail servers to RFC 821 section 4.5.1 commands of DATA, HELO, MAIL, NOOP, QUIT, RCPT, and RSET. This occurs via the Mail Guard service which is set with the following default configuration command: fixup protocol smtp 25 Another aspect of providing access to a mail server is setting being sure that you have a DNS MX record for the static's global address, which outside users access when sending mail to your site. |
access-list acl_out permit tcp any host | Create access to port 113, the IDENT protocol. If the mail server has to talk to many mail servers on the outside which connect back with the now obsolete and highly criticized IDENT protocol, use this access-list command statement to speed up mail transmission. The access-group command statement binds the access-list command statements to the outside interface. |
snmp-server host 192.168.3.2 | These commands specify that host 192.168.3.2 can receive SNMP events, which the PIX Firewall sends via syslog. The location and contact commands identify where the host is and who administers it. The community command describes the password in use at the SNMP server for verifying network access with the server. |
telnet 10.1.1.11 255.255.255.255 | These commands permit host access to the PIX Firewall console. The first telnet command permits a single host, 10.1.1.11 to access the PIX Firewall console with Telnet. The 255 value in the last octet of the netmask means that only the specified host can access the console. The second telnet command permits PIX Firewall console access from all hosts on the 192.168.3.0 network. The 0 value in the last octet of the netmask permits all hosts in that network access. However, Telnet only permits 16 hosts simultaneous access to the PIX Firewall console over Telnet. |
Three Interfaces without NAT
In Figure 4-4, the PIX Firewall has three interfaces. No address translation is performed between the interfaces.
Figure 4-4: Three-interface Configuration
The network has the following IP addresses and network masks:
- Outside network interface address: 209.165.201.2, network mask: 255.255.255.248
- Inside network interface address: 209.165.201.9, network mask: 255.255.255.248
- DMZ network interface address: 209.165.201.17, network mask: 255.255.255.248
Table 4-4 lists the configuration.
Table 4-4: Three Interfaces without NAT Configuration
| Configuration | Description |
|---|---|
nameif ethernet0 outside security0 | PIX Firewall provides nameif and interface command statements for the interfaces in the default configuration. Change the default auto option in the interface command to the specific line speed for the interface card. |
ip address outside 209.165.201.2 255.255.255.248 | Identify the IP addresses for each of the three interfaces. |
hostname pixfirewall | Specifies the host name for the PIX Firewall. This name appears in the command line prompt. |
arp timeout 14400 | Sets the ARP timeout to 14,400 seconds (four hours). Entries are kept in the ARP table for four hours before they are flushed. Four hours is the standard default value for ARP timeouts. |
no failover | Disables failover access. |
names | Lets you use text strings instead of IP addresses, which makes your configuration easier to read. |
pager lines 24 | Enables paging so that if when 24 lines of information display, PIX Firewall pauses the listing and prompts you to continue. |
logging buffered debugging | Enable syslog messages, which provide diagnostic information and status for the PIX Firewall. You can view the messages with the show logging command and clear the message buffer with the clear logging command. |
rip inside passive | Sets RIP listening attributes. The first two command statements enable RIP listening on the inside, but disable it on the outside. The no rip interface default commands causes PIX Firewall to not broadcast a default route on either interface. |
route outside 0.0.0.0 0.0.0.0 209.165.201.1 1 | Sets the outside default route to the gateway attached to the Internet. |
timeout xlate 3:00:00 | Default values for the maximum duration that PIX Firewall resources can remain idle until being freed. |
no snmp-server location | Specifies that SNMP information may be accessed by internal hosts that know the community string, but PIX Firewall does not send trap information to any host. |
mtu outside 1500 | Sets the maximum transmission unit value for Ethernet access. |
nat (inside) 0 209.165.201.8 255.255.255.248 | Disables NAT (Network Address Translation). |
static (dmz,outside) 209.165.201.19 209.165.201.19 | Maps access to the 209.165.201.19 host on the dmz interface. The access-list command lets any outside user access the host on any port. |
Three Interfaces with NAT
In Figure 4-5, the PIX Firewall has three interfaces and these attributes:
- Address translation is performed between the interfaces.
- A web server on the DMZ interface is publicly accessible. The name command maps its host address to the name "webserver."
- The inside network has illegal addresses (10.0.0.0), the DMZ interface has RFC 1597 addresses (192.168.0.0), and the outside network has legal, registered addresses (209.165.201.0).
- TCP and UDP connections from the inside are allowed to go out on the DMZ and outside.
- An inside host has been given Telnet access to the PIX Firewall console.
Figure 4-5: Three Interfaces with NAT
The network has the following IP addresses and network masks:
- Outside network interface address: 209.165.201.4, network mask: 255.255.255.224
- Allowable global and static addresses on the outside network: 209.165.201.5-209.165.201.30, network mask: 255.255.255.224
- Inside network interface address: 10.0.0.3, network mask: 255.0.0.0
- DMZ network interface address: 192.168.0.1, network mask: 255.255.255.0
Table 4-5 lists the configuration.
Table 4-5: Three Interfaces with NAT Configuration
| Configuration | Description |
|---|---|
nameif ethernet0 outside security0 | PIX Firewall provides nameif and interface command statements for the interfaces in the default configuration. Change the default auto option in the interface command to the specific line speed for the interface card. |
ip address outside 209.165.201.4 255.255.255.224 | Identify the IP addresses for each of the three interfaces. |
hostname pixfirewall | Specify the host name for the PIX Firewall. This name appears in the command line prompt. |
arp timeout 14400 | Set the ARP timeout to 14,400 seconds (four hours). Entries are kept in the ARP table for four hours before they are flushed. Four hours is the standard default value for ARP timeouts. |
no failover | Disable failover access. |
names | Lets you use text strings instead of IP addresses, which makes your configuration easier to read. |
pager lines 24 | Enable paging so that if after 24 lines of information display, PIX Firewall pauses the listing and prompts you to continue. |
logging buffered debugging | Enable syslog messages, which provide diagnostic information and status for the PIX Firewall. You can view the messages with the show logging command and clear the message buffer with the clear logging command. |
no rip inside passive | Disable RIP attributes. |
route outside 0.0.0.0 0.0.0.0 209.165.201.1 1 | Set the outside default route to the router attached to the Internet. |
access-list ping_acl permit icmp any any | Allow inbound and outbound pings. The "ping_acl" access-list command statement group is bound to the inside interface. The "acl_out" group is bound to the outside interface. This distinction accommodates the access-list command statement later in the configuration that applies permissions to a static command statement mapping. When troubleshooting is complete, remove the ICMP access-list statements. |
timeout xlate 3:00:00 | Default values for the maximum duration that PIX Firewall resources can remain idle until being freed. |
no snmp-server location | Specify that SNMP information may be accessed by internal hosts that know the community string, but PIX Firewall does not send trap information to any host. |
mtu outside 1500 | Set the maximum transmission unit value for Ethernet access. |
telnet 10.0.0.100 255.255.255.255 | Give Telnet access to PIX Firewall console to inside host. Use the timeout feature to set the maximum time a Telnet session can be idle before PIX Firewall closes the connection to 15 minutes. The default is 5 minutes. |
global (outside) 1 209.165.201.10-209.165.201.30 | Create a pool of global addresses for the outside and DMZ interfaces. Because there are limited outside IP addresses, add a PAT global to handle overflow. The global (dmz) command gives inside users access to the web server on the DMZ interface. |
nat (inside) 1 10.0.0.0 255.0.0.0 | Let inside users start connections on the DMZ and outside interfaces, and let DMZ users start connections on the outside interface. |
name 192.168.0.2 webserver | Give the IP address of the web server a label. |
static (dmz,outside) 209.165.201.6 webserver | Let any user on the outside interface access the web server on the DMZ interface. The access-list command statement is bound to the outside interface by the access-group command statement. |
Four Interfaces with NAT
In Figure 4-6, the PIX Firewall has four interfaces. In this configuration, there is no user authentication and no authorization. NAT (Network Address Translation) is in effect to translate addresses. In this example, users on all interfaces have access to all the servers and hosts on the inside, dmz1, and dmz2 interfaces can start connections.
This section includes the following topics:
- Guidelines for a Configuration with Four Interfaces
- IP Addresses for a Configuration with Four Interfaces
Figure 4-6: Four Interfaces with NAT
Guidelines for a Configuration with Four Interfaces
This section includes the following topics:
- Higher Security Level to Lower Security Level Access
- Lower Security Level to Higher Security Level Access
The most important guidelines to remember are as follows:
- Higher to lower—To let users on a higher security level interface access hosts on a lower security interface, use the nat and global commands; for example, to let users on the inside interface access the web server on the dmz2 interface. As seen in Figure 4-6, the inside interface has a security level of 100 and the dmz2 interface has a security level of 60.
- The nat command lets users access all hosts on all lower security level interfaces. The global command identifies the interface through which the nat access is permitted.
- Lower to higher—To let users on a lower security level interface access hosts on a higher security interface, use the static and access-list commands; for example, to let users on the dmz1 interface access the Telnet server on the inside interface. As seen in Figure 4-6, the dmz1 interface has a security level of 40 and the inside interface has a security level of 100.
- The static command lets users access specifically identified hosts on a single interface. The access-list command identifies the port or ports through which access is permitted. The access-group command binds the access-list command statement group to an interface.
The sections that follow provide more information on these guidelines.
Higher Security Level to Lower Security Level Access
To let users on each higher security level interface access servers on each lower security level interface, follow these steps:
Step 1 Letting higher security level interface users access a lower security level interface has two components: you use the nat command to specify from where users start connections, and you use the global command to specify to where access is permitted. You associate the nat and global commands together with the NAT ID, which in this example configuration is 1. The nat command lets users start connections from the specified interface to all lower security interfaces, the global command permits access to translated connections from any higher security level interface.
To let users from the inside interface start connections, use the following command:
nat (inside) 1 0 0
Step 2 To let users on the dmz2 interface start connections, use the following command:
nat (dmz2) 1 0 0
Step 3 To let users on the dmz1 interface start connections, use the following command:
nat (dmz1) 1 0 0
Step 4 To permit access to the dmz2 interface for translated connections, use the following command:
global (dmz2) 1 10.2.1.10-10.2.1.254
Step 5 To permit access to the dmz1 interface for translated connections, use the following command:
global (dmz1) 1 10.1.1.10-10.1.1.254
Step 6 To permit access to the outside interface for translated connections, use the following command:
global (outside) 1 209.165.201.10-209.165.201.30
Lower Security Level to Higher Security Level Access
To let users on a lower security level interface access a server on a higher security level interface, use the static and access-list commands. The first IP address in the static command is the address users on the lower security level interface use when they want to access the server on the higher security level interface. The second IP address is the actual address of the server.
When you enter the static command statement in your configuration, always specify the security level of the interfaces as (higher,lower) and the IP addresses as lower and higher; for example:
static (inside,dmz1) 10.1.1.7 10.0.1.2
When users on the dmz1 interface access the Telnet server, they use IP address 10.1.1.7.
To let users on each lower security level interface access servers on each higher security level interface, follow these steps:
Step 1 To let users on the outside interface access the mail server on the dmz1 interface, use the following command:
static (dmz1,outside) 209.165.201.5 10.1.1.2 netmask 255.255.255.255
access-list acl_out permit tcp any host 209.165.201.5 eq smtp
access-group acl_out in interface outside
The access-group command binds the "acl_out" access-list command statement group to the outside interface. The access-group command also applies to the other "acl_out" group access-list command statements that follow.
Step 2 To let users on the outside interface access the web server on the dmz2 interface, use the following command:
static (dmz2,outside) 209.165.201.6 10.2.1.2 netmask 255.255.255.255
access-list acl_out permit tcp any host 209.165.201.6 eq www
Step 3 To let users on the outside interface access the Telnet server on the inside interface, use the following command:
static (inside,outside) 209.165.201.7 10.0.1.2 netmask 255.255.255.255
access-list acl_out permit tcp any host 209.165.201.7 eq telnet
Step 4 To let users on the dmz1 interface access the web server on the dmz interface, use the following command:
static (dmz2,dmz1) 10.1.1.6 10.2.1.2 netmask 255.255.255.255
access-list acl_dmz1 permit tcp any host 10.1.1.6 eq www
access-group acl_dmz1 in interface dmz1
The access-group command binds the "acl_dmz1" access-list command statement group to the outside interface. The access-group command also applies to the other "acl_dmz1t" group access-list command statements that follow.
Step 5 To let users on the dmz1 interface access the Telnet server on the inside interface, use the following command:
static (inside,dmz1) 10.1.1.7 10.0.1.2
access-list acl_dmz1 permit tcp any host 10.1.1.7 eq telnet
Step 6 To let users on the dmz2 interface access the Telnet server on the inside interface, use the following command:
static (inside,dmz2) 10.2.1.7 10.0.1.2
access-list acl_dmz2 permit tcp any host 10.2.1.7 eq telnet
access-group acl_dmz2 in interface dmz2
All configuration command statements are explained in greater detail in Table 4-6.
Once you sketch out your network and map these steps to your IP addresses and servers, the four-interface configuration can become a simpler task.
IP Addresses for a Configuration with Four Interfaces
The addresses used in this configuration are as follows:
- The outside interface: 209.165.201.1 with static global addresses of 209.165.201.5 for the mail server on dmz1, 209.165.201.6 for the web server on dmz2, and 209.165.201.7 for the Telnet server on the inside. In addition, a pool of global addresses is defined as 209.165.201.10-209.165.201.30. A PAT (Port Address Translation) global is provided at 209.165.201.8.
- The dmz1 interface: 10.1.1.1 with static global addresses of 10.1.1.6 for the web server on dmz2 and 10.1.1.7 for the Telnet server on the inside. A pool of global addresses is defined as 10.1.1.10-10.1.1.254.
- The dmz2 interface: 10.2.1.1 with a static global address of 10.2.1.7 for the Telnet server on the inside and a pool of global addresses of 10.2.1.10-10.2.1.254.
- The inside interface: 10.0.1.1.
In addition, static route command statements are required to permit access to the networks that connect to the routers. A static route command statement directs traffic meant for a network to the router on the interface. The format for a static route command is shown in the following example:
route inside 10.0.2.0 255.255.255.0 10.0.1.3 1
This command statement instructs the PIX Firewall that when a packet needs to be sent to an address in the 10.0.2.0 network, send it to the router on the inside interface at 10.0.1.3.
Because there are routers on the inside, dmz2, and dmz1 interfaces with two networks connecting to each, six static route command statements are required—two for each interface.
Table 4-6 lists a four-interface configuration.
Table 4-6: Configuration with Four Interfaces
| Configuration | Description |
|---|---|
nameif ethernet0 outside security0 | PIX Firewall provides nameif and interface command statements for the interfaces in the default configuration. Change the default auto option in the interface command to the specific line speed for the interface card. |
ip address outside 209.165.201.1 255.255.255.224 | Identify the IP address for each interface. |
hostname pixfirewall | Specify the host name for the PIX Firewall. This name appears in the command line prompt. |
arp timeout 14400 | Set the ARP timeout to 14,400 seconds (four hours). This command statement is provided in the default configuration. |
no failover | Disable failover access. |
names | Lets you use text strings instead of IP addresses, which makes your configuration easier to read. |
pager lines 24 | Enable paging so that if after 24 lines of information display, PIX Firewall pauses the listing and prompts you to continue. |
logging buffered debugging | Enable syslog messages, which provide diagnostic information and status for the PIX Firewall. You can view the messages with the show logging command and clear the message buffer with the clear logging command. |
no rip inside passive | Disable RIP attributes. |
route outside 0.0.0.0 0.0.0.0 209.165.201.2 1 | Set the outside default route to the router attached to the Internet. |
access-list acl_in permit icmp any any | Allow inbound and outbound pings. When you are done ping testing, remove these lines. Permitting anyone to ping through the PIX Firewall adds extra overhead to the PIX Firewall and permits attackers to probe network vulnerabilities. The access-group commands for the "acl_out," "acl_dmz1," and "acl_dmz2" access-list command statement groups appear later in the configuration. |
timeout xlate 3:00:00 | Default values for the maximum duration that PIX Firewall resources can remain idle until being freed. |
no snmp-server location | Specify that SNMP information may be accessed by internal hosts that know the community string, but PIX Firewall does not send trap information to any host. |
mtu outside 1500 | Set the maximum transmission unit value for Ethernet access. You need to add the MTU command statements for the dmz1 and dmz2 interfaces. |
telnet 10.0.1.4 255.255.255.255 | Give Telnet access to PIX Firewall console to inside host. Use the timeout feature to let Telnet console sessions stay idle up to 15 minutes before PIX Firewall closes the connection. The default is 5 minutes. |
nat (inside) 1 0 0 | Let inside users start connections on all lower security level interfaces: dmz1, dmz2, and the outside. |
nat (dmz2) 1 0 0 | Let dmz2 users start connections on all lower security level interfaces: dmz1 and the outside. |
nat (dmz1) 1 0 0 | Let dmz1 users start connections on all lower security level interfaces, which in this case, is the outside. |
global (dmz2) 1 10.2.1.10-10.2.1.30 netmask | Give access to the dmz2 interface for users on the inside interface. This global command statement lets inside users access the dmz2 web server and provides access to the 10.2.2.0 and 10.2.3.0 networks. |
global (dmz1) 1 10.1.1.10-10.1.1.254 netmask | Give access to the dmz1 interface for users on the inside and dmz2 interfaces. This global command statement lets inside and dmz2 users access the dmz1 mail server and provides access to the 10.1.2.0 and 10.1.3.0 networks. |
global (outside) 1 209.165.201.10-209.165.201.254 | Create a pool of global addresses for the outside interface to permit users on all other interfaces to access the Internet. Because there are potentially more than 244 users on the 3 other interfaces, add a PAT global to handle overflow. |
static (dmz1,outside) 209.165.201.5 10.1.1.2 | Let outside users access the 10.1.1.2 mail server on the dmz1 interface. The outside users access the mail server via global address 209.165.201.5 on the outside interface. The access-list command statement lets users access the mail server on port 25 (smtp). The access-group command binds the "acl_out" access-list command statement group to the outside interface. The access-group command also applies to the other "acl_out" group access-list command statements that follow. |
static (dmz2,outside) 209.165.201.6 10.2.1.2 | Let outside users access the 10.2.1.2 web server on the dmz2 interface. The outside users access the web server via global address 209.165.201.6 on the outside interface. The access-list command statement lets users access the web server on port 80 (www). |
static (inside,outside) 209.165.201.7 10.0.1.2 | Let outside users access the 10.0.1.2 Telnet server on the inside interface. The outside users access the Telnet server via global address 209.165.201.7 on the outside interface. The access-list command statement lets users access the Telnet server on port 23 (telnet). |
static (dmz2,dmz1) 10.1.1.6 10.2.1.2 | Let dmz1 users access the 10.2.1.2 web server on the dmz2 interface. The dmz1 users access the web server via global address 10.1.1.6 on the dmz1 interface. The access-list command statement lets users access the web server on the WWW port (80). The access-group command binds the "acl_dmz1" access-list command statement group to the dmz1 interface. The access-group command also applies to the other "acl_dmz1" group access-list command statements that follow. |
static (inside,dmz1) 10.1.1.7 10.0.1.2 | Let dmz1 users access the 10.0.1.2 Telnet server on the inside interface. The dmz1 users access the Telnet server via global address 10.1.1.7 on the dmz1 interface. The access-list command statement lets users access the Telnet server on port 23 (telnet). |
static (inside,dmz2) 10.2.1.7 10.0.1.2 | Let dmz2 users access the 10.0.1.2 Telnet server on the inside interface. The dmz2 users access the Telnet server via global address 10.2.1.7 on the dmz2 interface. The access-list command statement lets users access the Telnet server on port 23 (telnet). The access-group command binds the "acl_dmz2" access-list command statement group to the dmz2 interface. |
route dmz1 10.1.2.0 255.255.255.0 10.1.1.3 1 | Provide static routes so that packets destined for the 10.1.2.0 and 10.1.3.0 networks are sent to the 10.1.1.3 router on the dmz1 interface. |
route dmz2 10.2.2.0 255.255.255.0 10.2.1.3 1 | Provide static routes so that packets destined for the 10.2.2.0 and 10.2.3.0 networks are sent to the 10.2.1.3 router on the dmz2 interface. |
route inside 10.0.2.0 255.255.255.0 10.0.1.3 1 | Provide static routes so that packets destined for the 10.0.2.0 and 10.0.3.0 networks are sent to the 10.0.1.3 router on the inside interface. |
Six Interfaces with NAT
In Figure 4-7, the PIX Firewall has six interfaces. In this configuration, there is no user authentication and no authorization. NAT (Network Address Translation) is in effect to translate addresses. In this example, users on all interfaces have access to all the servers and hosts on the inside, dmz1, dmz2, dmz3, and dmz4 interfaces can start connections.
This section includes the following topics:
- Guidelines for a Configuration with Six Interfaces
- IP Addresses for a Configuration with Six Interfaces
Figure 4-7: Six Interfaces with NAT
Guidelines for a Configuration with Six Interfaces
This section includes the following topics:
- Guidelines
- Higher Security Level to Lower Security Level Access
- Lower Security Level to Higher Security Level Access
Guidelines
The most important guidelines to remember follow:
- Higher to lower—To let users on a higher security level interface access hosts on a lower security interface, use the nat and global commands; for example, to let users on the inside interface access the mail server on the dmz2 interface. As seen in Figure 4-7, the inside interface has a security level of 100 and the dmz2 interface has a security level of 40.
- The nat command lets users access all hosts on all lower security level interfaces. The global command identifies the interface through which the nat access is permitted.
- Lower to higher—To let users on a lower security level interface access hosts on a higher security interface, use the static and access-list command statements; for example, to let users on the dmz1 interface access the Telnet server on the dmz2 interface. As seen in Figure 4-7, the dmz1 interface has a security level of 20 and the dmz2 interface has a security level of 40.
- The static command lets users access specifically identified hosts on a single interface. The access-list command identifies the port or ports through which access is permitted and the access-group command binds the access-list command statement group to an interface.
The sections that follow provide more information on these guidelines.
Higher Security Level to Lower Security Level Access
To let users on each higher security level interface access servers on each lower security level interface, follow these steps:
Step 1 Letting higher security level interface users access a lower security level interface has two components: you use the nat command to specify from where users start connections, and you use the global command to specify to where access is permitted. You associate the nat and global commands together with the NAT ID, which in this example configuration is 1. The nat command lets users start connections from the specified interface to all lower security interfaces, the global command permits access to translated connections from any higher security level interface.
- To let users from the inside interface start connections on the dmz1, dmz2, dmz3, dmz4, and outside interfaces, use the following command:
nat (inside) 1 0 0
- To let users on the dmz1 interface start connections on the outside, use the following command:
nat (dmz1) 1 0 0
- To let users on the dmz2 interface start connections on the dmz1 and outside interfaces, use the following command:
nat (dmz2) 1 0 0
- To let users on the dmz3 interface start connections on the dmz1, dmz2, and outside interfaces, use the following command:
nat (dmz3) 1 0 0
- To let users on the dmz4 interface start connections on the dmz1, dmz2, dmz3, and outside interfaces, use the following command:
nat (dmz4) 1 0 0
Step 2 Create global pools for the connections to start on each lower level interface:
- To permit access to the outside interface for translated connections from the inside, dmz1, dmz2, dmz3, and dmz4 interfaces, use the following command:
global (outside) 1 209.165.201.10-209.165.201.30 netmask 255.255.255.224
- To permit access to the dmz1 interface for translated connections from the inside, dmz2, dmz3, and dmz4 interfaces, use the following command:
global (dmz1) 1 10.1.1.10-10.1.1.254 netmask 255.255.255.0
- To permit access to the dmz2 interface for translated connections from the inside, dmz3, and dmz4 interfaces, use the following command:
global (dmz2) 1 10.2.1.10-10.2.1.254 netmask 255.255.255.0
- To permit access to the dmz3 interface for translated connections from the inside and dmz4 interfaces, use the following command:
global (dmz3) 1 10.3.1.10-10.3.1.254 netmask 255.255.255.0
Lower Security Level to Higher Security Level Access
To let users on a lower security level interface access a server on a higher security level interface, use the static and access-list command statements. The first IP address in the static command is the address users on the lower security level interface use when they want to access the server on the higher security level interface. The second IP address is the actual address of the server.
When you enter the static command statement in your configuration, always specify the security level of the interfaces as (higher,lower) and the IP addresses as lower and higher; for example:
static (inside,dmz1) 10.1.1.7 10.0.1.2
When users on the dmz1 interface access the Telnet server, they use IP address 10.1.1.7.
To let users on each lower security level interface access servers on each higher security level interface, follow these steps:
Step 1 To let users on the outside interface access the mail server on the dmz1 interface, use the following command:
static (dmz1,outside) 209.165.201.5 10.1.1.2 netmask 255.255.255.255
access-list acl_out permit tcp any host 209.165.201.5 eq smtp
access-group acl_out in interface outside
Step 2 To let users on the outside interface access the Telnet server on the dmz2 interface, use the following command:
static (dmz2,outside) 209.165.201.7 10.2.1.2 netmask 255.255.255.255
access-list acl_out permit tcp any host 209.165.201.7 eq telnet
Step 3 To let users on the dmz1 interface access the Telnet server on the dmz2 interface, use the following command:
static (dmz2,dmz1) 10.1.1.7 10.2.1.2
access-list acl_dmz1 permit tcp any host 10.1.1.7 eq telnet
access-group acl_dmz1 in interface dmz1
All configuration command statements are explained in greater detail in Table 4-7.
Once you sketch out your network and map these steps to your IP addresses and servers, the six-interface configuration becomes a simpler task.
IP Addresses for a Configuration with Six Interfaces
The addresses used in this configuration are as follows:
- The outside interface: 209.165.201.1 with static global addresses of 209.165.201.5 for the mail server on dmz1, 209.165.201.6 for the web server on dmz2, and 209.165.201.7 for the Telnet server on the inside. In addition, a pool of global addresses is defined as 209.165.201.10-209.165.201.30. A PAT (Port Address Translation) global is provided at 209.165.201.8.
- The dmz1 interface: 10.1.1.1 with static global addresses of 10.1.1.6 for the Telnet server on dmz2. A pool of global addresses is defined as 10.1.1.10-10.1.1.254.
- The dmz2 interface: 10.2.1.1 with a pool of global addresses of 10.2.1.10-10.2.1.254.
- The dmz3 interface: 10.3.1.1 with a pool of global addresses of 10.3.1.10-10.3.1.254.
- The dmz4 interface: 10.4.1.1 with a pool of global addresses of 10.4.1.10-10.4.1.254.
- The inside interface: 10.0.1.1 with a router at 10.0.1.4 and a host at 10.0.1.3.
In addition, static route command statements are required to permit access to the networks that connect to the routers. A static route command statement directs traffic meant for a network to the router on the interface. The format for a static route is shown in the following example:
route inside 10.0.2.0 255.255.255.0 10.0.1.4 1
This command statement instructs the PIX Firewall that when a packet needs to be sent to an address in the 10.0.2.0 network, send it to the router on the inside interface at 10.0.0.4.
Because there are routers on the inside, dmz1, and dmz4 interfaces with two networks connecting to each, six static route command statements are required—two for each interface.
Table 4-7 lists a six-interface configuration.
Table 4-7: Configuration with Six Interfaces
| Configuration | Description |
|---|---|
nameif ethernet0 outside security0 | PIX Firewall provides nameif command statements for all interfaces. In this case, the default perimeter names were changed to dmz1 through dmz4.
|
interface ethernet0 10baset | PIX Firewall provides interface command statements for all six interfaces in the default configuration. Change the default auto option in the interface command to the specific line speed for the interface card. |
ip address outside 209.165.201.1 255.255.255.224 | Identify the IP address for each interface. |
hostname pixfirewall | Specify the host name for the PIX Firewall. This name appears in the command line prompt. |
arp timeout 14400 | Set the ARP timeout to 14,400 seconds (four hours). This command statement is provided in the default configuration. |
no failover | Disable failover access. |
names | Lets you use text strings instead of IP addresses, which makes your configuration easier to read. |
pager lines 24 | Enable paging so that if after 24 lines of information displays, PIX Firewall pauses the listing and prompts you to continue. |
logging buffered debugging | Enable syslog messages, which provide diagnostic information and status for the PIX Firewall. You can view the messages with the show logging command and clear the message buffer with the clear logging command. |
no rip inside passive | Disable RIP attributes. Add command statements for the perimeter interfaces. |
route outside 0.0.0.0 0.0.0.0 209.165.201.4 1 | Set the outside default route to the router attached to the Internet. |
route dmz1 10.1.2.0 255.255.255.0 10.1.1.4 1 | Provide static routes so that packets destined for the 10.1.2.0 and 10.1.3.0 networks are sent to the 10.1.1.4 router on the dmz1 interface. |
route dmz4 10.4.2.0 255.255.255.0 10.4.1.4 1 | Provide static routes so that packets destined for the 10.4.2.0 and 10.4.3.0 networks are sent to the 10.4.1.4 router on the dmz4 interface. |
route inside 10.0.2.0 255.255.255.0 10.0.1.4 1 | Provide static routes so that packets destined for the 10.1.2.0 and 10.0.3.0 networks are sent to the 10.0.1.4 router on the inside interface. |
access-list acl_ping permit icmp any any | Allow inbound and outbound pings. When you are done ping testing, remove these command statements to prevent extra overhead and vulnerability from probing. The access-group command statements for the "acl_out" and "acl_dmz1" command groups appear later in the configuration. |
timeout xlate 3:00:00 | Default values for the maximum duration that PIX Firewall resources can remain idle until being freed. |
no snmp-server location | Specify that SNMP information may be accessed by internal hosts that know the community string, but PIX Firewall does not send trap information to any host. |
mtu outside 1500 | Set the maximum transmission unit value for Ethernet access. You need to add the MTU command statements for the perimeter interfaces. |
telnet 10.2.1.2 255.255.255.255 | Give Telnet access to PIX Firewall console to users on the Telnet server on dmz2 host. PIX Firewall checks the interface IP address to ensure it is an internal interface. This lets users outside the network Telnet to the server and then access the PIX Firewall console from the server. This is one method that can be used to troubleshoot or administer a PIX Firewall from a remote location. Use the timeout command feature to let Telnet console sessions stay idle up to 15 minutes before PIX Firewall closes the connection. The default is 5 minutes. |
nat (inside) 1 0 0 | Let inside users start connections on all lower security level interfaces: dmz1, dmz2, dmz3, dmz4, and the outside. |
nat (dmz1) 1 0 0 | Let dmz1 users start connections on the lower security level interface: the outside. |
nat (dmz2) 1 0 0 | Let dmz2 users start connections on all lower security level interfaces: dmz1 and the outside. |
nat (dmz3) 1 0 0 | Let dmz3 users start connections on all lower security level interfaces: dmz1, dmz2, and the outside. |
nat (dmz4) 1 0 0 | Let dmz4 users start connections on all lower security level interfaces: dmz1, dmz2, dmz3, and the outside. |
global (outside) 1 209.165.201.10-209.165.201.30 | Create a pool of global addresses for the outside interface to permit users on all other interfaces to access the Internet. Because there are a limited number of addresses in the global pool, add a PAT global to handle overflow. |
global (dmz1) 1 10.1.1.10-10.1.1.254 netmask | Give access to the dmz1 interface for users on the dmz2, dmz3, dmz4, and the inside interfaces. This global command statement lets users on access these interfaces access the dmz1 mail server and provides access to the 10.1.2.0 and 10.1.3.0 networks. |
global (dmz2) 1 10.2.1.10-10.2.1.254 netmask | Give access to the dmz2 interface for users on the inside interface. This global command statement lets inside users on the dmz3, dmz4, and inside access to the Telnet server of dmz2. |
global (dmz3) 1 10.3.1.10-10.3.1.254 | Give access to the dmz3 interface for users on the inside and dmz4 interfaces. |
global (dmz4) 1 10.4.1.10-10.4.1.254 netmask | Give access to the dmz4 interface for users on the inside interface which also permits access to the 10.4.2.0 and 10.4.3.0 networks connected to the 10.4.1.4 router. |
static (dmz1,outside) 209.165.201.6 10.1.1.2 netmask | Give outside users access to the mailserver on the dmz1 interface. |
static (dmz2,outside) 209.165.201.7 10.2.1.2 netmask | Give outside users access to the Telnet server on the dmz2 interface. |
static (dmz2,dmz1) 10.1.1.6 10.2.1.2 netmask | Give dmz1 users access to the Telnet server on the dmz2 interface. |
Failover Configuration
Figure 4-8 lists the network diagram for a failover configuration.
Figure 4-8: Failover Configuration
Follow these steps to configure the PIX Firewall units for use with failover:
Step 1 Set up the PIX Firewall without failover information.
Step 4 Use the write memory command on the Primary unit to save the new configuration.
Step 5 Plug the failover cable into the Primary unit and then power up the Secondary unit.
| Note If the Secondary unit has been previously configured, before you connect it to the failover cable to the Primary unit, boot it up, and enter the write erase command to remove any configuration. This will ensure a smooth synchronization. |
Example Configuration
In the example configuration in "Failover Configuration," the Ethernet2 interface (labeled "failover") is used as the dedicated interface for Stateful Failover. The Ethernet3 interface is a previously unconfigured interface and is currently not connected to any active network. There is a cross-over Ethernet cable connecting the unused interface so that the failover check up messages can be sent and received.
| Note PIX Firewall requires that unused interfaces be connected to the Standby unit and that each unused interface must be assigned an IP address. Even if an interface is administratively shut down, the PIX Firewall will try to send the failover check up messages to all internal interfaces. |
Table 4-8 lists the failover configuration.
Table 4-8: Failover Configuration
| Configuration | Description |
|---|---|
nameif ethernet0 outside security0 | These statements identify the four interfaces. The "failover" interface is connected to the other PIX Firewall unit for use by Stateful Failover to convey messages between the units. |
enable password xxx encrypted | These default configuration command statements are for the following:
|
no logging timestamp | The logging console errors command statement enables syslog message display at the console so that error, critical, and alert syslog messages are displayed. The logging facility 20 and logging queue 512 set the default values for the syslog message facility and message queue size. |
interface ethernet0 10baset | Set the interface command statements for the actual interface speed (do not use auto sensing with failover). Set ethernet2 for Stateful Failover (100 Mbps and full-duplex). |
mtu outside 1500 | The mtu command statements set the maximum transmission unit value to 1500 bytes, the default Ethernet setting. |
ip address outside 209.165.201.1 | The ip address command statements establish the IP addresses for each PIX Firewall interface. The outside interface is a NIC-registered address, whereas all other interfaces use the 192.168.n.n RFC 1918 Class C address. |
failover | The failover command statements enable failover and specify the IP addresses of each interface on the Standby unit. If you are using Stateful Failover, the failover link command specifies the name of the Stateful Failover interface, in this case, the "failover" interface. |
arp timeout 14400 | Specify that ARP refresh its table every 4 hours. |
global (outside) 1 209.165.201.3 netmask | Specify a PAT global for translating connections from the inside interface to the outside interface. Let all hosts on the inside start connections to the outside interface. |
static (inside,outside) 209.165.201.5 | Identify a global static address on the outside interface for a web server on the inside interface. The access-list command statements permit any host on the outside to access the inside web server on port 80, and to permit Pings on all interfaces. |
no rip outside passive | These rip command statements disable RIP listening on all interfaces. |
route outside 0 0 209.165.201.4 1 | Identify the outside router as the default router for the PIX Firewall. |
timeout xlate 3:00:00 | The timeout commands specify the maximum durations that PIX Firewall resources can remain idle until being freed. These values are the default intervals. |
aaa-server TACACS+ protocol tacacs+ | These command statements are part of the default configuration that perform the following purposes:
|