Routers
Routers can pass data from one network to another, and they allow for
filtering of data. Routers are best suited to connect your network to an outside
network, such as the Internet. If you have a web server for an internal intranet
that you do not want people to access from the Internet, for example, you can
use a router’s filter to block port 80 from outside your internal network. These
filters can be used to block specific hosts from accessing the Internet, as well.
For these reasons, routers are also called smart gateways.
Routers range in complexity and price from an enterprise-grade Cisco brand
router that can cost thousands of dollars to consumer brands designed for
home or small office use that can cost less than $50.
Initializing New Network Hardware
All the initial network configuration and hardware initialization for Ubuntu is
normally done during installation. At times, however, you may have to
reconfigure networking on your system, such as when a host needs to be
moved to a different subnet or a different network, or if you replace any of
your computer’s networking hardware.
Linux creates network interfaces in memory when the kernel recognizes that a
NIC or another network device is attached to the system. These interfaces are
unlike other Linux interfaces, such as serial communications ports, and they
do not have a corresponding device file in the /dev directory. Unless support
for a particular NIC is built in to your kernel, Linux must be told to load a
specific kernel module to support your NIC. More than 100 such modules are
located in the /lib/modules/2.6.XX-XX/kernel/net directory
(where XX-XX is your version of the kernel).
You can initialize a NIC in several ways when using Linux. When you first
install Ubuntu, automatic hardware probing detects and configures your
system to use any installed NICs. If you remove the original NIC and replace
it with a different make and model, your system will not automatically detect
and initialize the device unless you configure Ubuntu to use automatic
hardware detection when booting. Ubuntu should detect the absence of the
old NIC and the presence of the new NIC at boot time.
If you do not use automatic hardware detection and configuration, you can
initialize network hardware by doing the following:
Manually editing the /etc/modprobe.conf file to prompt the
system to recognize and support the new hardware upon reboot