You have a router and firewall in separate device. You review the possibility of setting the network:
1st Setup: ISP -- Router -- Firewall -- LAN 2nd Setup: ISP -- Firewall -- Router -- LAN
When there is an external modem to connect to the ISP, the modem is probably giving an Ethernet hand off. With this in mind, then it is possible to have the 2nd setup.
Several situations that might prevent you to have the 2nd setup are
* There is no external modem, and you have to use the integrated modem within the router * Your ISP requires PPPoA which your firewall is unable to support
When your situation falls within one of the above, then you have to have the 1st setup.
You Have The 1st Setup And Firewall Needs To Receive Public IP Address
There are several possibilities to setup
* Set a static NAT/PAT between the router and the firewall * Set the router to be a bridge/modem
Setting up a router as a bridge/modem might "downgrade" your router. Whenever possible, you then should consider setting static NAT/PAT between the router and firewall.
Case Studies
The 1st Setup: Router in front of Firewall
1. Router with integrated T1 modem terminates T1 circuit
This is using the 1st setup where the router is terminating T1 circuit with the ISP. In this case, the router is Cisco with integrated T1 modem and the firewall is PIX Firewall. This case study assumes that you have /29 IP block from your ISP where you can use one IP address for the router and another IP address for the PIX Firewall.
Router Configuration
no service pad service timestamps debug uptime service timestamps log uptime service password-encryption ! hostname Router ! boot-start-marker boot-end-marker ! logging buffered 4096 debugging no logging console ! clock timezone est -5 no aaa new-model ip subnet-zero no ip source-route ip cef ! ! no ip domain lookup ! no ip bootp server ! ! ! ! ! interface FastEthernet0/0 description LAN Interface ip address 192.168.100.1 255.255.255.252 ip nat inside no ip redirects no ip unreachables no ip proxy-arp no ip mroute-cache speed 100 full-duplex ! interface Serial0/0 description WAN Interface ip address 198.131.65.2 255.255.255.248 ip nat outside no ip redirects no ip unreachables no ip proxy-arp ip load-sharing per-packet no ip mroute-cache fair-queue service-module t1 timeslots 1-24 ! no ip http server ip classless ip route 0.0.0.0 0.0.0.0 198.131.65.1 ip route 192.168.101.0 255.255.255.0 192.168.100.2 ! ip nat inside source list 10 interface Serial0/0 overload ip nat inside source static 192.168.100.2 198.131.65.3 ! ! no cdp run ! line con 0 line aux 0 line vty 0 login line vty 0 4 login ! ! end
PIX Firewall Configuration
PIX Version 6.3(3) interface ethernet0 auto interface ethernet1 auto nameif ethernet0 outside security0 nameif ethernet1 inside security100 enable password ***** encrypted passwd ***** encrypted hostname PIX fixup protocol dns maximum-length 512 fixup protocol ftp 21 fixup protocol h323 h225 1720 fixup protocol h323 ras 1718-1719 fixup protocol http 80 fixup protocol rsh 514 fixup protocol rtsp 554 fixup protocol sip 5060 fixup protocol sip udp 5060 fixup protocol skinny 2000 fixup protocol smtp 25 fixup protocol sqlnet 1521 fixup protocol tftp 69 names pager lines 24 logging on logging trap informational mtu outside 1500 mtu inside 1500 ip address outside 192.168.100.2 255.255.255.252 ip address inside 192.168.101.2 255.255.255.0 ip audit info action alarm ip audit attack action alarm pdm history enable arp timeout 14400 nat (inside) 0 0.0.0.0 0.0.0.0 0 0 route outside 0.0.0.0 0.0.0.0 192.168.100.1 1 timeout xlate 3:00:00 timeout conn 1:00:00 half-closed 0:10:00 udp 0:02:00 rpc 0:10:00 h225 1:00:00 timeout h323 0:05:00 mgcp 0:05:00 sip 0:30:00 sip_media 0:02:00 timeout uauth 0:05:00 absolute aaa-server TACACS+ protocol tacacs+ aaa-server RADIUS protocol radius aaa-server LOCAL protocol local http server enable no snmp-server location no snmp-server contact snmp-server community public no snmp-server enable traps floodguard enable telnet timeout 5 ssh timeout 5 console timeout 0 terminal width 80
Description
•Public IP subnet is configured only on the router WAN side. The router LAN and PIX Firewall intefaces are using Private IP subnets •There is static NAT on the router in place between available Public IP address and the PIX Firewall outside interface to set the Firewall of "receiving" Public IP address •The LAN machines uses the router WAN interface to go out to the Internet
2. Router as PPPoA client to the ISP
This is using the 1st setup where the router is doing PPPoA as the ISP requirement to connect to the Internet. In this case, the router is Cisco with integrated DSL modem and the firewall is PIX Firewall. This case study assumes that you have /29 IP block from your ISP where you can use one IP address for the router and another IP address for the PIX Firewall.
Router Configuration
version 12.1 ! service timestamps debug datetime msec service timestamps log datetime msec ! hostname R1 ! ip subnet-zero ! interface Ethernet0 ip address 198.131.65.2 255.255.255.248 no ip directed-broadcast no ip mroute-cache ! interface ATM0 no ip address no ip directed-broadcast no ip mroute-cache no atm ilmi-keepalive pvc 1/150 encapsulation aal5mux ppp dialer dialer pool-member 1 ! hold-queue 224 in ! interface Dialer0 ip address unnumbered Ethernet0 no ip directed-broadcast encapsulation ppp dialer pool 1 dialer-group 1 ppp authentication chap callin ppp chap hostname username
ppp chap password password
! ip classless ! ip route 0.0.0.0 0.0.0.0 Dialer0 ! dialer-list 1 protocol ip permit ! end
•Do not setup router LAN or PIX Firewall outside interfaces yet; just the router Dialer interface •If you can setup the Dialer interface with static IP address without using the "ip negotiated", you can skip this Step 1. If you have to use the "ip negotiated", keep reading •Set the Dialer interface with the proper public IP address and the gateway using "ip negotiated" and "ip route" pointing to Dialer interface. Use the ipcp command to set the default gateway when possible •Do "show ip route" to find out the Dialer public IP address and gateway (the ISP equipment IP address)
Step 2: Configure LAN interfaces
•Move the Dialer public IP address to the Ethernet interface and set the Dialer as "ip unnumbered Ethernet" •Configure the PIX Firewall outside interface using the next available public IP address •Set the default gateway pointing to the ISP equipment IP address
1. One exit to ISP, Router performs NAT/PAT, PIX/ASA performs no NAT/PAT
This sample configuration assumes the followings:
* You have one ISP providing single path to your router * You set the router to do the NAT/PAT and basic firewall, where you leave the PIX to do the stateful firewall. * There is one ISP IP blocks you receive; the 1.1.0.0/30 where 1.1.0.1 is the default gateway and you use 1.1.0.2 (the only usable Public IP address for all servers and other machines in your LAN) * You are running servers visible to the public * The servers are web, mail, and ftp * Your internal webserver IP address is 10.10.11.2 * Your internal ftp server IP address is 10.10.11.3 * Your internal mail server IP address is 10.10.11.4 * You use 1.1.0.2 to be your three server's public IP address (static PAT) * You use a range of 1.0.1.30 to 1.0.1.254 to be your LAN workstations' public IP address (dynamic NAT and PAT) * You permit only internal host of 10.10.11.5 to telnet and to pdm to the PIX * Internal hosts are receiving IP address automatically (as DHCP clients) from the PIX * Since the PIX outside interface subnet is /30, there would be no other IP-based hosts between the PIX and the router within the same subnet
Router Configuration
! version 12.2 no parser cache no service single-slot-reload-enable no service pad service timestamps debug uptime service timestamps log uptime service password-encryption ! hostname Router ! logging buffered 4096 informational enable secret 5 ********** ! ip subnet-zero ! !!!!!!!!!!!!! This is the ISP's DNS IP addresses ip name-server 1.1.1.2 ip name-server 1.1.1.3 !!!!!!!!!!!!! ! ! ! ! ! !!!!!!!!!!!! This is the LAN side facing the PIX outside interface interface Ethernet0 ip address 10.10.10.1 255.255.255.252 ip nat inside no cdp enable ! !!!!!!!!!!!! This is to the ISP modem interface Ethernet1 ip address 1.1.0.2 255.255.255.252 ip nat outside no cdp enable ! ip classless ip route 0.0.0.0 0.0.0.0 1.1.0.1 ip route 10.10.11.0 255.255.255.0 10.10.10.2 no ip http server ! ip nat inside source static tcp 10.10.11.2 80 1.1.0.2 80 ip nat inside source static tcp 10.10.11.2 443 1.1.0.2 443 ip nat inside source static tcp 10.10.11.3 20 1.1.0.2 20 ip nat inside source static tcp 10.10.11.3 21 1.1.0.2 21 ip nat inside source static tcp 10.10.11.4 25 1.1.0.2 25 ip nat inside source static tcp 10.10.11.4 110 1.1.0.2 110 ip nat inside source list 1 interface Ethernet1 overload ! access-list 1 remark Permit Only Inside Subnets access-list 1 permit ip 10.10.8.0 0.0.3.255 no cdp run ! line con 0 exec-timeout 120 0 stopbits 1 line vty 0 4 exec-timeout 0 0 access-class 1 in login local length 0 ! scheduler max-task-time 5000 end
PIX Firewall Configuration
PIX Version 6.3(3) interface ethernet0 auto interface ethernet1 100full nameif ethernet0 outside security0 nameif ethernet1 inside security100 enable password ***** encrypted passwd ***** encrypted hostname pixfirewall fixup protocol dns maximum-length 512 fixup protocol ftp 21 fixup protocol h323 h225 1720 fixup protocol h323 ras 1718-1719 fixup protocol http 80 fixup protocol rsh 514 fixup protocol rtsp 554 fixup protocol sip 5060 fixup protocol sip udp 5060 fixup protocol skinny 2000 fixup protocol smtp 25 fixup protocol sqlnet 1521 fixup protocol tftp 69 names object-group network WEB network-object host 10.10.11.2 object-group network FTP network-object host 10.10.11.3 object-group network MAIL network-object host 10.10.11.4 object-group service MAIL_SERVICES tcp port-object eq smtp port-object eq pop3 object-group service WEB_SERVICES tcp port-object eq www port-object eq https access-list INBOUND permit icmp any any access-list INBOUND permit tcp any object-group WEB object-group WEB_SERVICES access-list INBOUND permit tcp any object-group MAIL object-group MAIL_SERVICES access-list INBOUND permit tcp any object-group FTP range ftp-data ftp access-list nonat permit ip any any pager lines 24 logging on logging console warnings logging monitor warnings mtu outside 1500 mtu inside 1500 ip address outside 10.10.10.2 255.255.255.252 ip address inside 10.10.11.1 255.255.255.0 ip audit info action alarm ip audit attack action alarm pdm location 10.10.11.5 255.255.255.255 inside pdm logging informational 100 pdm history enable arp timeout 14400 nat (inside) 0 access-list nonat access-group INBOUND in interface outside route outside 0.0.0.0 0.0.0.0 10.10.10.1 1 timeout xlate 3:00:00 timeout conn 1:00:00 half-closed 0:10:00 udp 0:02:00 rpc 0:10:00 h225 1:00:00 timeout h323 0:05:00 mgcp 0:05:00 sip 0:30:00 sip_media 0:02:00 timeout uauth 0:05:00 absolute aaa-server TACACS+ protocol tacacs+ aaa-server RADIUS protocol radius aaa-server LOCAL protocol local http server enable http 10.10.11.5 255.255.255.255 inside no snmp-server location no snmp-server contact snmp-server community public no snmp-server enable traps floodguard enable telnet 10.10.11.5 255.255.255.255 inside telnet timeout 5 ssh timeout 5 console timeout 0 dhcpd address 10.10.11.30-10.10.11.254 inside dhcpd dns 1.1.1.2 1.1.1.3 dhcpd enable inside terminal width 80 Cryptochecksum:3d7c056e8f90642f265cf42674b5a878 : end
2. Multiple exit to ISP (Failover Routing), Router performs no NAT/PAT, PIX/ASA performs NAT/PAT
This sample configuration assumes the followings:
* You have one ISP providing multiple path to your router * There is SLA between you and ISP in providing failover routing mechanism * You set the PIX to do the NAT/PAT and to provide stateful firewall features, where you leave the router to do the failover routing (source routing). * There are two ISP IP blocks you receive; the 1.0.0.0/24 and the 1.0.1.0/24 * The ISP path #1 subnet is 1.1.0.0/30 where the 1.1.0.2 is on your side * The ISP path #2 subnet is 1.1.0.4/30 where the 1.1.0.6 is on your side * Both 1.1.0.1 and 1.1.0.5 are on the ISP router that serve as your default gateway to the Internet * ISP router is set to use path #1 primary to reach the 1.0.0.0/24; and to use path #2 as alternate * Likewise, the ISP router is set to use path #2 primary to reach the 1.0.1.0/24; and to use path #1 as alternate * The network visible to your ISP are only the ones that they assign to you, which are the 1.1.0.0/29 and the 1.0.0.0/23. Other IP addresses or subnets are internal and are only visible to your network * You are running servers visible to the public * The servers are using 1.0.0.0/24 block and the workstations are using 1.0.1.0/24 block * The servers are web, mail, and ftp * Your internal webserver IP address is 10.10.11.2 * Your internal ftp server IP address is 10.10.11.3 * Your internal mail server IP address is 10.10.11.4 * You use 1.0.0.3 to be your three server's public IP address (static PAT) * You use a range of 1.0.1.1 to 1.0.1.254 to be your LAN workstations' public IP address (dynamic NAT and PAT) * You permit only internal host of 10.10.11.5 to telnet and to pdm to the PIX * Internal hosts are receiving IP address automatically (as DHCP clients) from the PIX * Since the PIX outside interface subnet is /30, there would be no other IP-based hosts between the PIX and the router within the same subnet
Router Configuration
! version 12.2 no parser cache no service single-slot-reload-enable no service pad service timestamps debug uptime service timestamps log uptime service password-encryption ! hostname Router ! logging buffered 4096 informational enable secret 5 ********** ! ip subnet-zero ! !!!!!!!!!!!!! This is the ISP's DNS IP addresses ip name-server 1.1.1.2 ip name-server 1.1.1.3 !!!!!!!!!!!!! ! ! ! ! ! !!!!!!!!!!!! This is the LAN side facing the PIX outside interface interface Ethernet0 ip address 10.10.10.1 255.255.255.252 no cdp enable ip policy route-map SourceRouting ! !!!!!!!!!!!! This is the ISP path #1 interface Ethernet1 ip address 1.1.0.2 255.255.255.252 no cdp enable ! !!!!!!!!!!!! This is the ISP path #2 interface Ethernet2 ip address 1.1.0.6 255.255.255.252 no cdp enable ! ip classless ip route 0.0.0.0 0.0.0.0 1.1.0.1 ip route 0.0.0.0 0.0.0.0 1.1.0.5 ip route 1.0.0.0 255.255.254.0 10.10.10.2 no ip http server ! access-list 101 remark Primary Route to ISP #1 access-list 101 permit ip host 1.0.0.3 any access-list 102 remark Primary Route to ISP #2 access-list 102 permit ip 1.0.1.0 0.0.0.255 any no cdp run ! route-map SourceRouting permit 10 match ip address 101 set ip next-hop 1.1.0.1 set interface Ethernet2 ! route-map SourceRouting permit 20 match ip address 102 set ip next-hop 1.1.0.5 set interface Ethernet1 ! line con 0 exec-timeout 120 0 stopbits 1 line vty 0 4 exec-timeout 0 0 login local length 0 ! scheduler max-task-time 5000 end
Note: This is just a sample configuration and not intended as working configuration on any network design. Your actual failover routing mechanism might be different than is suggested here due to the SLA between you and your ISP.
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 cableN * 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
service password-encryption ! hostname Router ! boot-start-marker boot-end-marker ! enable password 7 ****** ! memory-size iomem 25 clock timezone eastern -2 no aaa new-model ip subnet-zero ! ! ip name-server 68.87.64.196 ip name-server 68.87.66.196 ip dhcp excluded-address 192.168.100.1 192.168.100.5 ip dhcp excluded-address 192.168.100.254 ! ip dhcp pool INSIDE-LAN network 192.168.100.0 255.255.255.0 default-router 192.168.100.254 dns-server 68.87.64.196 68.87.66.196 ! no ip bootp server ip cef ! ! ! ! interface FastEthernet0 ip address 10.0.0.2 255.255.255.252 no ip redirects no ip proxy-arp speed auto duplex auto no cdp enable ! interface FastEthernet1 ip address 192.168.100.254 255.255.255.0 no ip redirects no ip proxy-arp speed 100 full-duplex no cdp enable hold-queue 100 out ! ip classless ip route 0.0.0.0 0.0.0.0 10.0.0.1 no ip http server ! logging history warnings logging 192.168.100.5 no cdp run ! line con 0 line aux 0 line vty 0 4 exec-timeout 120 0 password 7 ****** login ! end