The simplest form of a firewall is a packet filtering firewall.
Typically a router works as a packet-filtering firewall and has the capability to filter on some of the contents of packets.
On which of the following layers of the OSI reference model do these routers filter information? Each correct answer represents a complete solution.
Choose all that apply.
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A. B. C. D.DA.
Packet filtering firewall is the most basic form of firewall, which operates by examining the packets that flow in and out of a network and selectively blocking or allowing them based on predefined rules. Packet filtering firewall typically runs on routers, which have the capability to filter on some of the contents of packets.
In the OSI reference model, a router works as a network layer device, which means it operates at the third layer of the OSI reference model. The network layer is responsible for logical addressing and routing, which enables packets to be routed between different networks. The network layer header contains the source and destination IP addresses, which are used to determine the path that the packet should take through the network. The router examines the IP header of each incoming packet and compares it to a set of predefined rules to determine whether the packet should be forwarded or dropped.
Therefore, the correct answer is D. Network layer. Routers do not filter on the transport layer, physical layer, or data link layer. The transport layer is responsible for providing reliable data transfer between applications running on different hosts. The physical layer is responsible for transmitting raw bits over a physical medium. The data link layer is responsible for providing error-free transmission over a physical link. However, routers can filter on the transport layer port numbers, which are included in the TCP and UDP headers, to allow or block traffic based on the application protocol being used.