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CCNA 1.0 Network Hardware Firewall Technology Analysis

Network Security Fundamentals CCNA 1.0 Network Hardware Firewall Technology Analysis

The firewall technology was originally a protective measure taken against the insecure factors of the Internet network. As the name implies, a firewall is an internal network barrier used to block the impact of external insecurity, and its purpose is to prevent unauthorized access by external network users. It is a combination of computer hardware and software, which establishes a Security Gateway between the Internet and the Internet to protect the internal network from illegal users. The firewall is mainly composed of service access policies, authentication tools, and packet filtering. Composed of four parts: an application gateway, a firewall is a piece of software or hardware located between a computer and the network to which it is connected (of which hardware firewalls are rarely used only by the Department of Defense and other places because it is expensive). All network traffic in and out of this computer goes through this firewall.

The firewall has the references of network firewall and computer firewall. Network firewall refers to setting up a network firewall between the external network and the internal network. This firewall is also called a screening router. The network firewall detects the protocol, destination address, port (network layer) and transmitted information form (application layer) of incoming information, and filters out foreign information that does not comply with the regulations.

The firewall is not only used to control the Internet connection, but can also be used to protect the mainframe and important resources (such as data) within the organization’s network. Access to the protected data must be filtered by the firewall. Even if users inside the network want to access the protected data, they must also pass the firewall.

At present, the firewall in the device mainly refers to the following three types:

① Packet filtering firewall, that is, packet filtering based on ACL (Access Control List)

②  State firewall, namely ASPF (Application Specific Packet Filter, packet filtering based on application layer state)

③ Address conversion

Firewall related core technologies:

1. Packet filtering

The data on the network is transmitted in units of packets. Each packet contains some specific information, such as the source address, destination address, source port number, and destination port number of the data. The firewall reads the address information in the data packets to determine whether these packets come from a trusted network, and compares them with preset access control rules to determine whether the data packets need to be processed and operated. Packet filtering can prevent external illegal users from accessing the internal network, but because it cannot detect the specific content of the data packet, it cannot identify packets with illegal content and cannot implement security processing of application layer protocols.

2. Network IP address translation

Network IP address translation is a technology that converts private IP addresses into public network IP addresses. It is widely used in various types of networks and the Internet. On the one hand, network IP address translation can hide the real IP address of the internal network and protect the internal network from direct attacks by hackers. On the other hand, the internal network uses a private IP address, which effectively solves the problem of insufficient public network IP addresses.

3. Virtual private network

The virtual private network virtualizes a dedicated transmission channel through encrypted communication between local area networks or computers distributed in different regions, so as to logically connect them as a whole, not only saves the cost of building a dedicated communication line, but also effectively guarantees The security of network communication.

4. Application Gateway

The application-level gateway can check incoming and outgoing data packets, and pass the data through the gateway replication to prevent direct connection between trusted servers and clients and untrusted hosts. Application-level gateways can understand the protocols on the application layer, can do more complicated access control, and do detailed registration and auditing. It is aimed at a special network application service protocol, that is, data filtering protocol, and can analyze data packets and form related reports.

The English name of the firewall is “FireWall”, it is one of the most important network protection equipment. From a professional perspective, a firewall is a set of components located between two (or more) networks that implement access control between the networks.

A typical firewall has the following basic characteristics.

1. Nodes that the data stream must pass through:

All network data flow between the internal network and the external network must pass through the firewall. This is a characteristic of the network location where the firewall is located, and it is also a prerequisite. Because only when the firewall is the communication channel between the internal and external networks, can the network of the corporate network department be fully and effectively protected from infringement. The network structure of a typical firewall system is connected to the local area network of enterprises and institutions at one end, and the Internet at the other end. All communication between the internal and external networks must pass through the firewall, and only data streams that comply with security policies can pass through the firewall.

2. Make sure that network traffic must be compliant:

The most basic function of the firewall is to ensure the legitimacy of network traffic, and on this premise, the network traffic is quickly forwarded from one link to another link.

3. Anti-attack characteristics

This is the prerequisite for the firewall to be able to take on the important task of internal network security protection. The reason why it has such a strong firewall operating system itself is the key, only the operating system with its own complete trust relationship can talk about the security of the system. Of course, these security can only be said to be relative.

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