Appliance Control: Making Things Do Stuff - Smart Home Automation with Linux and Raspberry Pi - page 40

This host section can be included within the subnet section shown previously to create exceptions in the
pooling rule.
You can determine which leases have been granted by typing the following:
more /var/lib/dhcp3/dhcpd.leases
Many other options are available in the DHCP server, but these provide enough to get everything working.
I'll cover the specific extra cases as appropriate.
Computer Names
My name is Steven, often shortened to Steev. My computer's name is 192.168.1.110, which is less easy to remember
for nongeeks. Chances are there will be more nongeeks in your house than geeks who will want to refer to each
computer by a name such as “Holly's computer” or “Angela's laptop.” There are two strains of problem here: getting
the computers in the house to have usable names and getting them to know the names of each computer outside the
house on the Internet.
Computer names are usually distributed automatically around the local network, so they are not a problem,
although it can sometimes take 30 seconds for the information to propagate to all machines. In case of problems, you
can force-feed a mapping between IP addresses and computer names by adding a line like this:
192.168.1.110 mediapc
to the file located at /etc/hosts or C:\WINDOWS\SYSTEM32\DRIVERS\etc\hosts depending on whether you're working
on Linux or Windows, respectively.
Converting Internet domain names into numbers is done through a type of server known as Domain Name
System (DNS). This is a simple client/server process whereby a client provides a domain name, such as google.com ,
and the server returns the globally accessible IPv4 address of the computer. There are many of these servers
throughout the world, arranged in a hierarchy. So, if your local DNS server doesn't know about a particular domain,
it will ask its parent DNS server, and so on, all the way up to the master root zone server. All you need to do is configure
your home machines to use the first DNS server in this chain, and the searches will happen automatically. If your ISP
has provided you with a DNS server address, you can use this directly. Alternatively, if you are using a router, then this
will often configure itself automatically by looking for a DNS server on the external part of the network (which only it
can see) and then act as a DNS relay whereby it pretends to be a DNS server for internal network but instead passes all
requests the ISP's DNS, before returning the results to you.
Having got an IP address of the DNS server (you'll use the 192.168.1.1 of the router in this example), you can
use the DHCP server to distribute this information to each machine when it also requests an IP address of its own.
Because the same DNS server is used for all local machines, this can be done by setting the global option at the top of
the /etc/dhcpd.conf file:
option domain-name-servers 192.168.1.1;
Alternatively, if you are not using DHCP to provide the networking credentials, then you must revert to the same
/etc/network/interfaces file in which you specified its static address and add the following:
dns-nameservers 192.168.1.1