The Debian installation software provides for the configuration of the network as early as possible in the installation process. This creates the potential for performing the remainder of the installation from a network mounted device.
The network installation process is concerned with the construction of three configuration files:
/etc/hosts
/etc/resolv.conf
/etc/init.d/network
It does so by collecting the following information:
Host Name
Domain Name
Full Name
IP address
Netmask
Network Address
Broadcast Address
Gateway Address
Nameserver Addresses
The Host Name is the name given to the machine itself. The installation software provides the name debian as the default value. Any ``reasonable'' string of characters can be used as a host name, but normally this is intended to be readable and should thus be a legitimate name. On some local area networks these names are determined by the network administrator. In this case the name will need to be supplied by the administrator. The Domain Name is typically the name of the network (i.e. planetlinux.com) that the machine is connected to. This will also be supplied by the network administrator. If the machine connects to the Internet through an Internet Service Provider (ISP) then the domain name is typically the domain of the provider.
The Full Name is constructed from the Host Name and the Domain Name. If the machine is named fred and the domain is somewhere.net then the full name becomes: fred.somewhere.net. This is the name that others will use when attempting to contact this machine with telnet or FTP or any other remote login client, so this represents the ``complete address'' of the machine in question. Typically a ``name server'' is used to convert this ``full name'' into an IP address for the site. When a site is not accessible with its full name, but is accessible by its IP address, this indicates that the system being used has no DNS facilities available or the IP address hasn't been registered through the Internic. Declaration of these servers is done in /etc/resolv.conf and will be discussed in detail later in this section.
The IP Address that corresponds to the Full Name is a string made up out of the numbers between 0 and 255 and the dot (.) character. A typical IP address has the form: 192.64.1.1 and represents the ``address'' of the target machine. If your ISP can provide ``static'' IP addresses, you will be able to declare the address that they assign, at installation time. If your connection to the Internet uses dynamic IP addressing, supply the address 0.0.0.0 as a value to fill the entry.
The Netmask is a string of bits used to determine whether a given address is on the local sub-net or outside of it. Debian installation assumes a class C network and provides the default value of 255.255.255.0. This value is used to compute several other addresses for the system. If the machine belongs to a broader (or more restricted) network the system administrator will know the correct value to provide for the netmask.
The Network Address, the Broadcast Address, and the Gateway Address are all constructed from the machine IP Address and the Netmask. In our example above, the Netmask of 255.255.255.0 ``masked'' (logical AND) against the IP Address, 192.64.1.1, gives the Network Address of 192.64.1.0. To obtain the Broadcast Address, the Netmask is first inverted, to become 0.0.0.255 and a logical OR performed with the Network Address, yielding a Broadcast Address of 192.64.1.255 for our example machine. The address of the machine on the local net that connects to the rest of the Internet is know as the Gateway Address. These machines are known as routers and typically are the first (but sometimes the last) address on the local net. This would imply that our example IP address, 192.64.1.1, is that of a router. In this case the machine is its own gateway, which is fine depending on your setup.
The last set of information involves Name Servers. When you can ping an IP Address but can't ping the equivalent Full Name then there is a name server missing or not configured. If the machine connects to the Internet via an ISP, then they will provide the name server and will be able to declare the correct address. If the machine is connected by Ethernet the local system administrator will provide that information. The Debian installation will accept up to 5 name servers for entry into /etc/resolv.conf to be used for name lookup.
The /etc/hosts file from our example above would look like:
127.0.0.1 localhost
192.64.1.1 fred.somewhere.net
While /etc/resolv.conf might look like:
domain somewhere.net
search somewhere.net
nameserver 192.64.1.1
nameserver 199.44.34.2
and, if there is an Ethernet card in the machine
/etc/init.d/network
might look like:
#! /bin/sh
# Configure the loopback device
ifconfig lo 127.0.0.1
route add 127.0.0.1
# Configure the Ethernet device
ifconfig eth0 192.64.1.1
route add -net 192.64.1.0
route add -net 0.0.0.0 gw 192.64.1.1
If you still have questions about the correct values for the various addresses and masks that will be requested during the installation ask the local network administrator or your Internet Service Provider, depending on which provides the Internet access for the machine.