A Network Tutorial for
Brazil Firewall and Coyote Linux

If your know this stuff skip to BrazilFW install OR Coyote Linux Setup

For Internet connectivity these four requirements are necessary.
1) a TCP/IP stack.
2) an IP address.
3) A gateway on the same network as the IP address.
4) A DNS server.

A typical Coyote Linux/BrazilFW setup has 3 basic scenarios: PPPoE (telephone company high-speed connection), DHCP (cable company connection), and PPP (telephone dial-up) using a standard modem. Both PPPoE and DHCP use a high speed ADSL modem. Both cable and telephone companies also have static connections using a ADSL modem. Administer your ADSL modem with BrazilFW.If you are using a telephone dial-up connection then see my PPP dial-up services page for a description of setting up the modem and PC along with troubleshooting information.

A typical setup (PPPoE or DHCP) works right out of the box as if you had bought a D-Link or Linksys router from a store except that you have better control and options. Try my 2 network trick with a Linksys. The components are a modem usually supplied by the Internet Service Provider (ISP). Then there is your BrazilFW/Coyote Linux computer which will act as a router, firewall, Domain Name System (DNS) server, and Dynamic Host Configuration Protocol (DHCP) server. Lastly there is your client computer(s) to which you want to provide Internet connectivity.

With more than one client PC there will be a switch to which you connect the Network Interface Card (NIC) of each computer and the Local Area Network (LAN) NIC of Coyote Linux/Brazil Firewall. With only one client PC, the NIC of the client can connect to the LAN NIC of your firewall using a crossover cable or normal cable with a crossover adapter. The other firewall NIC is the Wide Area Network (WAN). This is connected to the modem which is connected to your ISP in whichever way you were instructed.

The rules of TCP/IP networking say that all PCs on a network must use IP addresses in the same network range or they can't talk. This is written as 192.168.0.0/24 and it means IPs 192.168.0.1 through 192.168.0.254 and 255.255.255.0 as a network mask. 192.168.0.0 is reserved to mean "the network" and 192.168.0.255 is reserved as a broadcast address. We will not get into subnets.Here are 2 IP calculators to demonstrate netmasks, broadcast address, and stuff.
IP CIDR calculator   IP calculator using an IP address range.It may seem ridiculous to mention but two computers cannot have the same IP address on a network just like two people cannot have the same e-mail address.

A router connects to two (or more) different networks and routes between them. In our case this is your 192.168.0.0/24 and n.n.n.n/n which belongs to the ISP but is assigned to you.Again it may seems ridiculous to mention but a router has a different network addresses on each side. 192.168.0.1 and 192.168.0.100 are not two different networks.Plugging both cables (LAN and WAN) into the same switch along with the ADSL modem is not correct. It may work but is still not correct.

When a PC needs to talk to another network it does this through its default gateway (router). This is BrazilFW/Coyote Linux. A PC also needs a DNS server to resolve domain names (google.ca) to IP addresses. This is also Coyote Linux/Brazil Firewall.All PCs need this configuration to surf so you can hard code each PC or let Coyote Linux/BrazilFW do it for you with DHCP. A standard install will use 192.168.0.1 as its IP address and should have DNS and DHCP enabled.Save yourself headaches and remove all the gateway and DNS addresses on all your clients. No more rules, no nothing. That's it. End of story. It works.

Your ISP will supply your firewall with its configuration via the WAN NIC just like you supply your clients with their configuration via the LAN NIC. If you have a DHCP configuration don't mix up these two ideas even though the same term, DHCP, is used to describe both. The firewall is a DHCP client to the ISP and a DHCP server to the PCs. The PCs are DHCP clients to Coyote Linux/BrazilFW.