Computer Networking And Management
...router and an application gateway (sometimes referred as an application proxy)
What does firewall means? As far as my knowledge goes, firewall is some kind of system or group of systems which enables to control access and sets privileges between two networks. The most common boundary in firewall is between a trusted and an un-trusted network. A perfect and secure firewall would not interfere with users’ activities or any transfers between authorized networks. Network firewalls mainly operate in different layers of the OSI model. The lowest layer in which the firewall operates is in the network layer. In this layer the internet protocol for TCP/IP will determine if the packet is from a trusted source. Special privileges cannot be assigned to grant access or deny in this layer. Firewall which works at the highest layer of OSI layer is on Application layer, where granting access is more easy because at application layer a large collection of information including the source and packet contents will be known. The network would be more secure if packets are intersected and analyzed at lowest levels of OSI model. It is mere impossible to gain access for an intruder pass the third layer of OSI model.
A great feature of router is that it has the ability to block the flow of broadcasts between network segments. Routers also have the ability to filter out certain traffic. That is when two networks are connected there are certain data the destination network should be able to access from the main network. To grant this, IP filtering is configured in to the routers so this would enable encryption and security and will prevent unauthorized access.
Cisco routers provide a couple of methods for filtering traffic. The simplest is Standard Access List, which enables to filter from a certain subnet range to a specific IP address. Extended Access Lists are used for advance IP...
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