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firewall
Network Layer
The firewall that only allows packets of registered connection is called packet filter. It is also the central piece in firewalling.
Incoming packets must be legitimate responses to requests from internal hosts. Unsolicited packets are blocked unless permitted specifically. SPI can also include the capability to recognize and filter out specific types of attacks such as DoS.
firewall
Since the fundamental task of a firewall is to filter packets, the weak point in its traditional behavior is the fact that it also must route packets after a decision is made. Can the model be simplified? Of course it can, and the answer comes by stepping down a layer in the OSI model. Instead of the device handling packets at layer 3 (network), what if it merely inspected frames and moved them to the proper interface? Sound familiar? This type of device would continue to filter packets, but operate at layer 2 (data link), like a bridge. Such a device has come to be known by several names: a transparent, in-line, shadow, stealth or bridging firewall. ranajoy karmakar@gmail.com ccna,network engineer
packet filter firewall
Means Firewall Packet Filter.
firewall, router,layer 3 switches and i approve that answer ! NO! In general the firewall is a layer 4 device, it traffics filter incoming and outgoing ports. It uses the function of TCP and UCP. However a Firewall can also be a layer 3 device as in internal firewall in a router. Also a switch is a layer 2 device unless your talking about a Router switch.
Capture filter or a pre-filter