计算机网络基础(翻译版)Computer Network Basic青云网
1、 Fundamentals of Communication Protocol Stack
Introduction to OSI protocol stack 2. Detailed explanation of TCP
protocol 3. Detailed explanation of IP address 4. Gateway, DNS, ARP, and
communication foundation2、 Exchange technologyExchange basics 2. VLAN introduction 3. STP detailed explanation3、 Routing technologyStatic routing 2. RIP protocol 3. OSPF protocol4、 Applied TechnologyDHCP principle 2. Telnet principle 3. FTP protocol5、 Access Control Technology and NATACL access control list 2. NAT network address translation1 Fundamentals of Communication ProtocolIntroduction to OSI Protocol StackI. The OSI model is divided into seven layers:Physical layer – Data link layer – Network layer – Transport layer – Session layer – Presentation layer – Application layerII
The OSI seven layer model enables reliable communication between
different systems and networks through seven hierarchical structural
models. Therefore, its main function is to help different types of hosts
achieve data transmission. The node that completes the relay function
is usually referred to as a relay system.Equipment on each layer:Physical layer: network card, network cable, hub, repeater, modemData link layer: bridge, switchNetwork layer: routerThe gateway operates at or above the fourth layer transport layerVI. Functions of each device:Hub: A physical layer device that transmits information through broadcasting.Switch: used for packet exchange.Bridge:
When a bridge works, it determines the forwarding port based on the MAC
header, so it is obviously a device in the data link layer.Router:
One function is to connect different networks, and the other function is
to select the route for information transmission.2、 Exchange technologyExchange FoundationThe exchange technology in computer networks
is actually how the hosts at both ends of the computer network transmit
data packets through the network. For example, in the telephone system,
two main switching technologies are used: circuit switching technology
and packet switching technology.From the perspective of
communication resource allocation, “switching” is to dynamically
allocate the resources of transmission lines in a certain way.VLAN IntroductionVLAN is a virtual local area network, where a
VLAN forms a logical subnet, i.e. a logical broadcast domain. VLANs work
in the second and third layers of the OSI reference model, and
communication between VLANs is completed through routing in the third
layer.The role of VLAN: avoiding broadcast storms, ensuring security, and facilitating managementSTP ExplanationIn order to improve network reliability,
redundant links are usually used in switching networks. However.
Redundant links can bring loop risks to switching networks, leading to
broadcast storms and unstable MAC address tables, which in turn can
affect the communication quality of users. The Spanning Tree Protocol
(STP) can improve reliability while avoiding various issues caused by
loops.The principle of STP protocol: Block a certain interface in
the network (logically), achieve normal physical link connection,
logically close (down), and avoid the harm of the loop.3、 Routing technologyStatic routingA routing method where routing entries are
manually configured rather than dynamically determined. Unlike dynamic
routing, static routing is fixed and will not change, even if the
network conditions have changed or been reconfigured. Generally
speaking, static routing is added item by item to the routing table by
the network administrator.RIP protocolRIP is applied to the application layer of the OSI
network’s seven layer model.. RIP is a distributed distance vector based
routing protocol, which was introduced by Xerox in the 1980s and is
mainly suitable for small-scale network environments.Working principle:Using
neighbor’s routing table to establish its own routing table: When
receiving a routing table from a neighbor, the router will update its
routing table:Firstly, add 1 to the distance of the received route (i.e. the distance of one hop);Reuse the received routing table to modify one’s own routing tableOSPF protocolOpen Shortest Path First (OSPF) was developed in
1989 to overcome the shortcomings of RIP. The principle of OSPF is
simple, but its implementation is complexOSPF routing protocol is a
link state routing protocol used for Internet Protocol (IP) networks.
This protocol uses the Internal Gateway Protocol (IGP) of the Link State
Routing algorithm and operates within a Single Autonomous System (AS)The
OSPF protocol relies on five different types of packets to establish
adjacency relationships and exchange routing information, namely
greeting packets, database description packets, link state request
packets, link state update packets, and link state confirmation packets4、 Applied TechnologyDHCP principleDHCP Dynamic Host Configuration Protocol is a
network protocol for a local area network that operates using the UDP
protocol and has two main purposes: automatically assigning IP addresses
to internal networks or network service providers, and serving as a
central management tool for users or internal network administrators to
manage all computers.Telnet principleRelogin was developed for Berkeley UNIX and is a
relatively simple and stable protocol that has been adopted by users
outside the UNIX community. TELNET is a feature rich TCP/IP standard. It
is the most widely used protocol in the TCP/IP protocol family. Provide
a universal tool for accessing internet resources in a connected
manner, allowing users to communicate with servers on a remote machine,
supporting different physical terminals through a negotiation process,
thereby providing great flexibility. The following diagram shows the
typical structure of TELNET client and server.Working principle:TELNET
maps terminals to a logical device using consistent standards, enabling
data exchange between clients and servers across different types of
terminals.The main body of the TELNET protocol consists of three parts:Ÿ The definition of Network Virtual Terminal (NVT);Ÿ Definition of operation negotiation;Ÿ Negotiate finite automata;FTP protocolThe File Transfer Protocol is a standard protocol
used for file transfer over a network. It operates at the seventh layer
of the OSI model and the fourth layer of the TCP model, which is the
application layer. It uses TCP transmission instead of UDP. Before
establishing a connection with the server, customers need to go through a
“three handshake” process to ensure that the connection between the
client and the server is reliable and connection oriented, providing
reliable guarantees for data transmission.Working principle:It
uses two TCP connections between two communicating hosts, one for data
transmission; The other is the control connection, which is used to
transmit control information (commands and responses). This idea of
separating command and data transmission greatly improves the efficiency
of FTP, while other client server applications generally only have one
TCP connection.5、 Access Control Technology and NATACL access control listAccess Control List (ACL) is a packet
filtering based access control technique that filters packets on an
interface based on set conditions, allowing them to pass or drop. Access
control lists are widely used in routers and layer three switches. With
the help of access control lists, users can effectively control their
access to the network, thereby maximizing network security.Access
control lists have many functions, such as limiting network traffic and
improving network performance; Control of communication flow.NAT network address translationWhen some hosts within the
private network have already been assigned a local IP address (i.e. a
dedicated address used only within the private network), but want to
communicate with hosts on the Internet (without encryption), the NAT
method can be used. This method requires the installation of NAT
software on the router connecting the private network (private IP) to
the internet (public IP).NAT not only solves the problem of
insufficient IP addresses, but also effectively avoids attacks from
outside the network, hides and protects computers inside the network.Broadband sharing: This is the biggest feature of NAT hosts.Security protection: When a PC within NAT is connected to the
Internet, the displayed IP is the public IP of the NAT host, so the
client PC naturally has a certain degree of security. When external
parties perform portscan, the source client PC cannot be detected.
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