PCs send their requests to the Internet via the firewall, which acts as a representative of the PCs to the Internet. The target system therefore sees only the firewall, which in turn forwards the response packets of the target system to the appropriate PC on the internal network.
Depending on the type of firewall it is able to analyze the network packets in both directions and filter them, even before they reach the actual communication partner. Connection of an external firewall that restricts access between the Internet and the private (self-contained) network as handled by the Computer Service Centre Sydney.
Example configuration: The internet can be accessed via DSL connection, including DSL modem. The firewall could then be installed on a DSL router, which is addressed by the PCs in the private (self-contained) network as a default gateway. The device managed by the network requests the internal PCs and can distinguish between requests to the internal (private) and external network (Internet) and forward them accordingly.
The switch connects the PCs on the internal network with each other and is usually integrated in such a firewall, but is deliberately presented as an independent unit, to clarify that a firewall only allows access between the internal and external network filters, but has no effect on communication in the internal network.
Since the target system from the Internet does not see the internal PC, but only the firewall, possible attacks from the Internet are directed to the predestined firewall and not directly to the computer. Someone trying to intercept this connection by looking for a network address (such as file and printer sharing), will not find it because the service is not running on the PC, but on the firewall.
At this level, the firewall is therefore not vulnerable and the network services of the internal PCs are unreachable. Also, a malicious software that might be secretly installed a network service on the PC, can not alter that state. The network service is accessible only from the private network out, but not vice-versa (the malware can eventually install a service on the firewall, but only on the PC).
For the described functionality, it is necessary that the firewall device has been configured accordingly (the protected computer system must not be used as “standard server” or exposed host as shown by the Computer Service Centre Sydney.
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