ccna 2020

ccna 2020.As networks continue to evolve, they are increasingly used to transmit and store sensitive data. This has increased the need for security technology, and as a result, firewalls have been created. The term firewall derives from a fireproof wall, usually made of stone or metal, used to stop the spread of flames between connected buildings. Similarly, in networks, firewalls isolate protected areas from unprotected areas, blocking unauthorized users from accessing resources in the protected network.Initially, basic access control lists (ACLs),including standard, extended, numeric, and named, were the only means of providing firewall protection. Other firewall technologies began in the late 1990s. Stateful firewalls use state tables to track the real-elbow state of end-to-end sessions. It takes into account the session-oriented nature of network traffic. The first stateful firewalls used the "TCP established" option of ACLs. Later, self-reversing ACLs are used to dynamically reflect the specific type of outbound traffic when it returns an answer. The purpose of developing dynamic ACLs is to open a. hole in the firewall to release approved traffic over a period of time. The purpose of developing a time-based ACL is to implement an ACLo As the number of ACL types increases, it becomes increasingly important to verify the correct behavior of ACLs with the show and debug commands.Today, many firewalls exist, including packet filtering, stateful inspection, application gateways (proxies), address translation, host-based, transparent, and hybrid firewalls. Modern network design must include the correct placement of one or more firewalls to protect those resources that must be protected, while allowing secure access to them.4.1 Access Control Lists4.1.1 Configuring Standard and Extended IPv4 ACLs with the CLI4.1.1.1 Introduction to ACLsAccess Control Lists (ACLs) are widely used in computer networks to mitigate network attacks and control network traffic in the context of network security. Administrators use ACLs to define and control different kinds of traffic on network devices based on a variety of different parameters. These parameters are specific to layers 2, 3, 4, and 7 of the OSI model.Nearly all types of traffic can be defined explicitly using appropriately numbered ACLs. For example, the type field in the previous Ethernet frame header can be used to define a specific type of traffic. Ethernet Type 0x8035 indicates a reverse address resolution protocol4.1 Access Control Lists 81(RARP) frame. Numbered ACLs in the range 200.299 are used to control traffic based on the Ethernet type.