Network Appliance for Packet State Verification

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The network appliance that checks the state of a packet to determine whether the packet is legitimate is a firewall.

A firewall is a network security device that monitors and controls incoming and outgoing network traffic based on predetermined security rules. Firewalls can be hardware, software, or a combination of both.

Firewalls work at different layers of the OSI model, but most commonly at the network and transport layers (layers 3 and 4). They examine each packet that enters or leaves a network and compare it to a set of predefined rules.

The firewall then decides whether to allow or block the packet based on the rules. The rules can be based on various criteria, such as the source and destination IP addresses, the port numbers, and the protocol being used.

Firewalls can also be configured to perform additional security functions, such as intrusion detection and prevention, content filtering, and VPN connectivity.

In summary, a firewall is a network appliance that checks the state of a packet to determine whether the packet is legitimate based on predefined rules and is an essential component of network security infrastructure.