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Using Linux To Share An Optus Cable Modem - Part 2

Installing a name server (DNS) & a DHCP server.

By John Bagster.

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Fig.6: you can use the (list) command to check that both named and dhcpd have been installed. You should get responses similar to those shown here in green.

It's always a good idea to install both DNS and DHCP servers when using a Linux gateway to the Internet and that applies whether you are using a cable modem or a dial-up connection. Both servers are easy to get going under Linux and they make setting up your Windows boxes a snack.

So what exactly are the functions of these two server utilities and how do they make life easier? We'll start by explaining the role of the Domain Name server (DNS).

DNS servers play a vital role when it come to navigating the Internet. Basically, their job is to translate domain names into their corresponding IP addresses. This means, for example, that you can go to the SILICON CHIP website by typing in instead of typing the IP address into your web browser: ie,

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Fig.7: use a text editor to modify the /etc/rc.d/init.d/dhcpd file as shown here - ie, append "eth0" after "daemon /usr/sbin/dhcpd" (no quote marks).

Typically, you make use of the DNS servers (also known simply as "name" servers) provided by your ISP. This means that, during setup, you have to enter the IP addresses for these servers at the DNS Configuration tab in the TCP/IP Properties dialog box on each of your Windows machines - see Fig.5 last month. Note that there will usually be at least two name servers - a primary DNS server and a backup DNS server.

One potential problem with this is that the two nameserver lines in /etc/resolv.conf (on the Linux box) may change - eg, if your ISP changes the IP address of one or more of their name servers. This means that you would then have to manually change them on all your Windows PCs or in the DHCP configuration setup that follows. The standard lease time for the Optus modem is 12 hours, meaning that the information in /etc/resolv.conf could change every 12 hours (although this is very unlikely).

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