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Ports
If you accept the analogy of IP addresses being rather like telephone numbers,
then think of ports as extension numbers. In a company of any size, you
generally wouldn’t expect the accounts department to share the same telephone
with the technical department. Although their calls may all be related to the
same company, they concern very different aspects of that company.
It is the same with IP network connections. Although you have only one network
link into your computer and only one IP address (phone number), you are
probably performing many different tasks through that one link, often at the
same time. Thus, when you browse the web your outgoing requests and the
incoming information are all channelled through port 80. When you send an
email, it travels through port 25 and when you transfer files you are, without
knowing it, using port 20.
At the “border crossing” between the wider Internet and every local network
attached to it, there is a router that is usually combined with a firewall. One of
its main tasks is to direct incoming traffic to the correct place within its local
network. A key piece of information to help it do this is the port number:
Security issues with ports
The settings of port numbers become important when the AdderView CATx IP
is situated behind a network firewall. In order for a remote VNC viewer or web
browser to make contact with your AdderView CATx IP, it is necessary for the
firewall to allow communication through a particular numbered port to occur.
One specific function of firewalls is to restrict access to ports in order to prevent
malicious attackers using them as a route into your network. Every new port that
is opened offers a new possibility for hackers and so the number of accessible
ports is purposefully kept to a minimum. In such cases, it may be advantageous
to change one or both AdderView CATx IP ports to use the same number. The
other alternative is to place the AdderView CATx IP unit outside the firewall and
take full advantage of its secure operation features – see
Networking issues for
details.
IMPORTANT: The correct configuration of routers and firewalls requires
advanced networking skills and intimate knowledge of the particular network.
Adder Technology cannot provide specific advice on how to configure your
network devices and strongly recommend that such tasks are carried out by a
qualified professional.
AdderView CATx IP has
the local IP address:
192.168.0.3
User with VNC viewer accesses
IP address: 129.7.1.10 (this
automatically uses port 5900).
Router/firewall address: 129.7.1.10
Router is programmed to send port 5900
VNC traffic to local address 192.168.0.3
and port 80 web traffic to local address
192.168.0.42
User accesses the company
website at: 129.7.1.10 (this
automatically uses port 80).
Web server has the local
IP address: 192.168.0.42