3.7 Network Devices
Networks consist of numerous devices which have to be connected to each other. This
happens with the help of a network device. There are different types of network devices
which will be described in the following.
3.7.1 Hub
A hub is a device that combines all the connected network devices into one network segment.
In other words packets that are transmitted through a hub will be forwarded to every
connected network device and not just to the device that is to be addressed. Nowadays hubs
have mainly been replaces by switches.
3.7.2 Switch
A switch is an intelligent hub that remembers the MAC addresses of the connected interface
and can therefore forward packets with a certain destination to that destination without having
to send them to all connected interfaces.
3.7.3 Access Point
A wireless access point is a device that connects WLAN adapters in a wireless network. Often
an access point is connected to a wired network and provides access to this network to the
WLAN adapters.
3.7.4 Router
While hubs and switches connect devices to local networks, routers connect different
networks. In other words routers are devices that make a network seem like a single IP
address to other networks. This is done through a process called NAT.
3.8 NAT (Network Address Translation)
Network Address Translation was introduced to overcome a shortage of IP addresses. It is a
technique which rewrites source and/or destination IP addresses in packets when they pass
through a router or a firewall. This feature is mostly used to allow multiple hosts in a private
network to access the internet.
Normally every host that wants to access the internet has to have a registered IP address.
Unfortunately IP adresses are of limited quantity. NAT makes it possible to have multiple
hosts in a private network (for example in the private IP range 192.168.x.x or 10.x.x.x) which
are connected to a router which is the interface to the internet. The router modifies the packets
in a way that the remote host that should be accessed only sees the external IP address of the
router. Answers are sent to the router which modifies the packets and relays them to the host
in the private network that sent the actual request.
