ccna 300-201 dump

ccna 300-201 dump.state firewall and application gateway firewall.4.2.2.2 Packet Filtering FirewallsPacket filtering firewalls work primarily at the network layer of the OSI model. Firewalls are generally considered to be Layer 3 devices, but can also deny or allow traffic based on Layer 4 information (e.g., protocol, source and destination port numbers). Packet filtering uses ACLs and determines whether to allow or deny traffic based on source and destination IP addresses, protocols, source and destination port numbers, and packet types. Packet filtering firewalls are usually part of a router firewall.Services depend on specific ports to function. For example, an SMTP server listens on port 25 by default. Because packet filtering firewalls filter traffic based on static information in packet headers, they are also often referred to as static filters. By restricting specific ports, administrators can limit the services that depend on those ports. For example, blocking port 25 on a workstation can prevent an infected workstation from spreading a virus throughout the network via E-mail.Packet filtering firewalls use simple policy table lookups and determine whether to allow or deny traffic based on specific criteria: source address.the destination IP address; the protocol; the source port number; the destination port number.4.2 Firewall Techniques 103Synchronization/start (SYN) to receive packets.The following are some of the benefits of using a packet filtering firewall. Packet filters can be implemented using a simple allow or deny rule set. Packet filters have a low impact on network performance. Packet filters are easy to implement and are supported by most routers. Packet filters provide a minimum level of security at the network layer. Packet filters can perform almost most of the tasks of a high-end firewall at a low cost.Here are some of the downsides of using a packet filter firewall.