Decentralization of tcpip protocol
Publish: 2021-04-15 15:57:06
1. =TEXT(C1*100,"[ Dbnum2] RMB: ten million one hundred thousand yuan and Jiao 0 Fen only
2. The abbreviation of transmission control protocol / Internet protocol, which is translated into Chinese as transmission control protocol / Internet Interconnection Protocol, also known as network communication protocol, is the most basic protocol of Internet and the foundation of Internet. It is composed of IP protocol of network layer and TCP protocol of transmission layer. TCP / IP defines how electronic devices connect to the Internet and how data is transmitted between them. The protocol adopts a four layer hierarchical structure, and each layer calls the network provided by its next layer to fulfill its own requirements. Generally speaking: TCP is responsible for finding the problem of transmission. When there is a problem, it will send out a signal to request retransmission until all data is safely and correctly transmitted to the destination. In terms of protocol layer model, TCP / IP consists of four layers: network interface layer, network layer, transport layer and application layer. TCP / IP protocol does not fully conform to OSI's seven layer reference model. OSI is a traditional open system interconnection reference model, which is a seven layer abstract reference model of communication protocol, in which each layer performs a specific task. The purpose of this model is to make all kinds of hardware communicate with each other at the same level. The seven layers are: physical layer, data link layer, network layer, transport layer, session layer, presentation layer and application layer. The TCP / IP communication protocol adopts a four layer hierarchical structure, and each layer calls the network provided by its next layer to complete its own task. Since the designers of ARPNET pay attention to network interconnection and allow the communication subnet (network interface layer) to adopt various existing or future protocols, there is no special protocol in this layer. In fact, TCP / IP protocol can be connected to any network through the network interface layer, such as X.25 switching network or IEEE802 LAN
the physical layer defines various characteristics of physical media: 1. Mechanical characteristics. 2. Electronic properties. 3. Functional characteristics. 4. Procere characteristics. The data link layer is responsible for receiving IP datagrams and sending them through the network, or receiving physical frames from the network, extracting IP datagrams and delivering them to the IP layer. Common interface layer protocols are: Ethernet 802.3, token ring 802.5, X.25, frame relay, HDLC, PPP ATM, etc< The network layer is responsible for the communication between adjacent computers. Its functions include three aspects. 1、 After receiving the request, the packet is loaded into the IP datagram, the header is filled, the path to the destination machine is selected, and then the datagram is sent to the appropriate network interface. 2、 Processing input datagram: first check its validity, and then carry out pathfinding - if the datagram has arrived at the sink machine, remove the header and hand over the rest to the appropriate transport protocol; If the datagram has not arrived at the sink, the datagram is forwarded. 3、 Deal with path, flow control, congestion and other issues. The network layer includes: IP (Internet Protocol), ICMP (Internet control message protocol), ARP (address resolution protocol) and RARP (reverse ARP). IP is the core of the network layer, and the next hop IP is encapsulated and delivered to the interface layer through routing. IP datagram is a connectionless service. ICMP is a supplement to the network layer and can send back messages. Used to detect whether the network is unobstructed. Ping command is to send ICMP echo packet, and test the network by echo relay. ARP is a forward address resolution protocol, through the known IP, to find the corresponding host MAC address. RARP is a reverse address resolution protocol, which determines IP address by MAC address. Such as diskless workstation and DHCP service
transport layer
provides communication between applications. Its functions include: 1. Format information flow; 2、 Provide reliable transmission. In order to realize the latter, the transport layer protocol stipulates that the receiver must send back an acknowledgement, and if the packet is lost, it must be retransmitted. Transport layer protocol is mainly: transmission control protocol (TCP) and user datagram protocol (UDP)
application layer
provides users with a set of common applications, such as e-mail, file transfer access, remote login, etc. Telnet uses telnet protocol to provide interfaces registered on other hosts in the network. Telnet session provides character based virtual terminal. File transfer access FTP uses FTP protocol to provide file function between machines in the network. The application layer is generally a user oriented service. Such as FTP, Telnet, DNS, SMTP, POP3. FTP (File Transfer Protocol) is a file transfer protocol. Generally, FTP service is used for upload and download. The data port is 20h and the control port is 21h. Telnet service is a user's remote login service, which uses 23h port and clear code transmission, with poor confidentiality, simple and convenient. DNS (domain name service) is a domain name resolution service, which provides domain name to IP address conversion. SMTP (Simple Mail Transfer Protocol) is a simple mail transfer protocol, which is used to control the sending and transferring of mail. POP3 (post office protocol 3) is the third version of post office protocol, which is used to receive mail
the protocols in the network layer mainly include IP, ICMP, IGMP, etc. because it contains IP protocol mole, it is the core of all networks based on TCP / IP protocol. In the network layer, IP mole completes most of the functions. ICMP, IGMP and other IP supporting protocols help IP accomplish specific tasks, such as transmitting error control information and control messages between hosts and routers. The network layer is in charge of the information transmission between hosts in the network. The main protocols on the transport layer are TCP and UDP. Just as the network layer controls the data transmission between hosts, the transport layer controls the data that will enter the network layer. Two protocols are the two ways it manages these data: TCP is a connection based protocol; UDP is a management protocol for connectionless services. The main shortcomings of TCP / IP model are: firstly, the model does not clearly distinguish which is the specification and which is the implementation; Secondly, the host network layer of the TCP / IP model defines the interface between the network layer and the data link layer, which is not a layer in the conventional sense. The difference between the host network layer and the interface layer is very important. The TCP / IP model does not distinguish them
data format
data frame: frame header + IP packet + frame tail (frame header includes MAC address and type of source and target host, frame tail is check word) IP packet: IP header + TCP data information (IP header includes IP address, type, lifetime, etc. of source and target host) TCP data information: TCP header + actual data (TCP header includes port number, sequence number, confirmation number, etc. of source and target host) Background
at the beginning of ARPA, there were not many computers connected by interface signal processor, and most computers were not compatible with each other. It was difficult to get the work done on one computer to another computer, and it was also difficult to connect computers with different hardware and software. At that time, the situation in the United States was that the computers used in the army were Dec series procts, the computers used in the Navy were Honeywell's winning machines, and the computers used in the air force were IBM's winning machines. The computers of each service were running well in their respective departments, but there was a big drawback: they could not share resources. At that time, scientists put forward such a concept: "all computers are born equal." In order for these "born equal" computers to realize "resource sharing", it is necessary to establish a standard that everyone must abide by on top of these system standards, so that different computers can "negotiate" according to certain rules and "shake hands" after negotiation. In the process of determining the "negotiation rules" between computers on the Internet today, the most important person is Vinton g. Cerf. It is his efforts that enable today's various computers to connect to the Internet according to the protocol. As a result, Cerf got the same reputation as Kleinrock ("father of the Internet") "father of the Internet". Since childhood, Cerf likes to be unconventional, strong and enthusiastic. When he was in high school, he was allowed to use the UCLA computer. He thought that "programming a computer is a very exciting thing... As long as you program it well, you can let the computer do anything." In 1965, Cerf graated from Stanford University and worked as a system engineer in an IBM company. Not long after he worked, Cerf felt that his knowledge was not enough, so he went to UCLA to study for a doctorate. At that time, it was the establishment of ARPANET, the research and test of interface signal processor (IMP) and the establishment of network evaluation center, Cerf also became a student of Kleinrock, a famous scientist. Cerf and three other young people (Winfield, Crocker and Braden) participated in the connection of the first node of ARPANET. Shortly after that, Bob Kahn, who has a strong judgment on the development of various situations at work and is recognized as making a great contribution to the construction of ARPANET, also came to UCLA. In those days, it was often Kahn who proposed what software he needed, while Cerf worked all night to compile the software that met the requirements, and then they tested the software together until it worked properly. At that time, the main pattern was as follows: Roberts proposed the network idea to design the network layout, Kahn designed the overall structure of ARPANET, Klein rock was responsible for the network evaluation system, and many scientists and graate students participated in the research and experiment. After ARPANET was born and put into operation in September, 69, it was found that when each imp was connected, it was necessary to consider opening the communication pipeline with signals recognized by all kinds of computers, and closing the channel after the data passed through. Otherwise, these imps will not know when to receive signals and when to end. This is the concept of communication "Protocol". In December of 1970, the original communication protocol was formulated, which was developed by Kahn and participated by Cerf. However, it is not easy to establish a common standard. After the international computer communication conference ended in October of 72, scientists are working hard for this“ The "packet switching" theory provides a theoretical basis for the connection between networks. On the basis of his own research, Kahn realized that only by deeply understanding the details of various operating systems can he establish a universal protocol for various operating systems. In 73, Kahn asked Cerf to consider all the details of this protocol together. The result of their cooperation proced the "transmission control protocol" (TCP), which is currently used by all Internet users and network managers under the open system, Transmission control protocol and internet protocol are TCP / IP protocol. Generally speaking: TCP is responsible for finding the problem of transmission. When there is a problem, it will send out a signal to request retransmission until all data is safely and correctly transmitted to the destination. IP is an address for every computer on the Internet. In December 1974, Kahn and Cerf's first detailed description of TCP protocol was officially published. At that time, the U.S. Department of defense signed the TCP / IP protocol with three teams of scientists. As a result, the team led by Cerf was the first to formulate the TCP / IP protocol standard through detailed definition. At that time, an experiment was carried out to pass packets through a point-to-point satellite network, then through land cables, and then through satellites
the physical layer defines various characteristics of physical media: 1. Mechanical characteristics. 2. Electronic properties. 3. Functional characteristics. 4. Procere characteristics. The data link layer is responsible for receiving IP datagrams and sending them through the network, or receiving physical frames from the network, extracting IP datagrams and delivering them to the IP layer. Common interface layer protocols are: Ethernet 802.3, token ring 802.5, X.25, frame relay, HDLC, PPP ATM, etc< The network layer is responsible for the communication between adjacent computers. Its functions include three aspects. 1、 After receiving the request, the packet is loaded into the IP datagram, the header is filled, the path to the destination machine is selected, and then the datagram is sent to the appropriate network interface. 2、 Processing input datagram: first check its validity, and then carry out pathfinding - if the datagram has arrived at the sink machine, remove the header and hand over the rest to the appropriate transport protocol; If the datagram has not arrived at the sink, the datagram is forwarded. 3、 Deal with path, flow control, congestion and other issues. The network layer includes: IP (Internet Protocol), ICMP (Internet control message protocol), ARP (address resolution protocol) and RARP (reverse ARP). IP is the core of the network layer, and the next hop IP is encapsulated and delivered to the interface layer through routing. IP datagram is a connectionless service. ICMP is a supplement to the network layer and can send back messages. Used to detect whether the network is unobstructed. Ping command is to send ICMP echo packet, and test the network by echo relay. ARP is a forward address resolution protocol, through the known IP, to find the corresponding host MAC address. RARP is a reverse address resolution protocol, which determines IP address by MAC address. Such as diskless workstation and DHCP service
transport layer
provides communication between applications. Its functions include: 1. Format information flow; 2、 Provide reliable transmission. In order to realize the latter, the transport layer protocol stipulates that the receiver must send back an acknowledgement, and if the packet is lost, it must be retransmitted. Transport layer protocol is mainly: transmission control protocol (TCP) and user datagram protocol (UDP)
application layer
provides users with a set of common applications, such as e-mail, file transfer access, remote login, etc. Telnet uses telnet protocol to provide interfaces registered on other hosts in the network. Telnet session provides character based virtual terminal. File transfer access FTP uses FTP protocol to provide file function between machines in the network. The application layer is generally a user oriented service. Such as FTP, Telnet, DNS, SMTP, POP3. FTP (File Transfer Protocol) is a file transfer protocol. Generally, FTP service is used for upload and download. The data port is 20h and the control port is 21h. Telnet service is a user's remote login service, which uses 23h port and clear code transmission, with poor confidentiality, simple and convenient. DNS (domain name service) is a domain name resolution service, which provides domain name to IP address conversion. SMTP (Simple Mail Transfer Protocol) is a simple mail transfer protocol, which is used to control the sending and transferring of mail. POP3 (post office protocol 3) is the third version of post office protocol, which is used to receive mail
the protocols in the network layer mainly include IP, ICMP, IGMP, etc. because it contains IP protocol mole, it is the core of all networks based on TCP / IP protocol. In the network layer, IP mole completes most of the functions. ICMP, IGMP and other IP supporting protocols help IP accomplish specific tasks, such as transmitting error control information and control messages between hosts and routers. The network layer is in charge of the information transmission between hosts in the network. The main protocols on the transport layer are TCP and UDP. Just as the network layer controls the data transmission between hosts, the transport layer controls the data that will enter the network layer. Two protocols are the two ways it manages these data: TCP is a connection based protocol; UDP is a management protocol for connectionless services. The main shortcomings of TCP / IP model are: firstly, the model does not clearly distinguish which is the specification and which is the implementation; Secondly, the host network layer of the TCP / IP model defines the interface between the network layer and the data link layer, which is not a layer in the conventional sense. The difference between the host network layer and the interface layer is very important. The TCP / IP model does not distinguish them
data format
data frame: frame header + IP packet + frame tail (frame header includes MAC address and type of source and target host, frame tail is check word) IP packet: IP header + TCP data information (IP header includes IP address, type, lifetime, etc. of source and target host) TCP data information: TCP header + actual data (TCP header includes port number, sequence number, confirmation number, etc. of source and target host) Background
at the beginning of ARPA, there were not many computers connected by interface signal processor, and most computers were not compatible with each other. It was difficult to get the work done on one computer to another computer, and it was also difficult to connect computers with different hardware and software. At that time, the situation in the United States was that the computers used in the army were Dec series procts, the computers used in the Navy were Honeywell's winning machines, and the computers used in the air force were IBM's winning machines. The computers of each service were running well in their respective departments, but there was a big drawback: they could not share resources. At that time, scientists put forward such a concept: "all computers are born equal." In order for these "born equal" computers to realize "resource sharing", it is necessary to establish a standard that everyone must abide by on top of these system standards, so that different computers can "negotiate" according to certain rules and "shake hands" after negotiation. In the process of determining the "negotiation rules" between computers on the Internet today, the most important person is Vinton g. Cerf. It is his efforts that enable today's various computers to connect to the Internet according to the protocol. As a result, Cerf got the same reputation as Kleinrock ("father of the Internet") "father of the Internet". Since childhood, Cerf likes to be unconventional, strong and enthusiastic. When he was in high school, he was allowed to use the UCLA computer. He thought that "programming a computer is a very exciting thing... As long as you program it well, you can let the computer do anything." In 1965, Cerf graated from Stanford University and worked as a system engineer in an IBM company. Not long after he worked, Cerf felt that his knowledge was not enough, so he went to UCLA to study for a doctorate. At that time, it was the establishment of ARPANET, the research and test of interface signal processor (IMP) and the establishment of network evaluation center, Cerf also became a student of Kleinrock, a famous scientist. Cerf and three other young people (Winfield, Crocker and Braden) participated in the connection of the first node of ARPANET. Shortly after that, Bob Kahn, who has a strong judgment on the development of various situations at work and is recognized as making a great contribution to the construction of ARPANET, also came to UCLA. In those days, it was often Kahn who proposed what software he needed, while Cerf worked all night to compile the software that met the requirements, and then they tested the software together until it worked properly. At that time, the main pattern was as follows: Roberts proposed the network idea to design the network layout, Kahn designed the overall structure of ARPANET, Klein rock was responsible for the network evaluation system, and many scientists and graate students participated in the research and experiment. After ARPANET was born and put into operation in September, 69, it was found that when each imp was connected, it was necessary to consider opening the communication pipeline with signals recognized by all kinds of computers, and closing the channel after the data passed through. Otherwise, these imps will not know when to receive signals and when to end. This is the concept of communication "Protocol". In December of 1970, the original communication protocol was formulated, which was developed by Kahn and participated by Cerf. However, it is not easy to establish a common standard. After the international computer communication conference ended in October of 72, scientists are working hard for this“ The "packet switching" theory provides a theoretical basis for the connection between networks. On the basis of his own research, Kahn realized that only by deeply understanding the details of various operating systems can he establish a universal protocol for various operating systems. In 73, Kahn asked Cerf to consider all the details of this protocol together. The result of their cooperation proced the "transmission control protocol" (TCP), which is currently used by all Internet users and network managers under the open system, Transmission control protocol and internet protocol are TCP / IP protocol. Generally speaking: TCP is responsible for finding the problem of transmission. When there is a problem, it will send out a signal to request retransmission until all data is safely and correctly transmitted to the destination. IP is an address for every computer on the Internet. In December 1974, Kahn and Cerf's first detailed description of TCP protocol was officially published. At that time, the U.S. Department of defense signed the TCP / IP protocol with three teams of scientists. As a result, the team led by Cerf was the first to formulate the TCP / IP protocol standard through detailed definition. At that time, an experiment was carried out to pass packets through a point-to-point satellite network, then through land cables, and then through satellites
3. The abbreviation of transmission control protocol / Internet protocol, which is translated into Chinese as transmission control protocol / Internet Interconnection Protocol, also known as network communication protocol, is the most basic protocol of Internet and the foundation of Internet. It is composed of IP protocol of network layer and TCP protocol of transmission layer. TCP / IP defines how electronic devices connect to the Internet and how data is transmitted between them. The protocol adopts a four layer hierarchical structure, and each layer calls the protocol provided by its next layer to fulfill its own requirements. Generally speaking: TCP is responsible for finding the problem of transmission. When there is a problem, it will send out a signal to request retransmission until all data is safely and correctly transmitted to the destination. IP is to specify an address for each Internet device.
4. Unknown_Error
5. Sorry, I don't know which setting you need to set in TCP / IP, filter or other services based on TCP / IP, please add
ah! You can find the network neighborhood - right click "properties" - and then find "local connection" - "properties" - double click "Internet Protocol (TCP / IP)" to set the IP, mask and DNS of this machine
ah! You can find the network neighborhood - right click "properties" - and then find "local connection" - "properties" - double click "Internet Protocol (TCP / IP)" to set the IP, mask and DNS of this machine
6. Introction to TCP / IP protocol
communication protocol of TCP / IP
this part briefly introces the internal structure of TCP / IP, so as to lay a foundation for the discussion of Internet related security issues. TCP / IP protocol group is popular in part because it can be used on a variety of channels and underlying protocols (such as T1 and X.25, Ethernet and RS-232 serial interface). To be exact, TCP / IP protocol is a group of protocols including TCP protocol and IP protocol, UDP (User Datagram Protocol), ICMP (Internet control message protocol) and other protocols<
overview of the overall architecture of TCP / IP
TCP / IP protocol does not fully conform to the seven layer reference model of OSI. The traditional open system interconnection reference model is a seven layer abstract reference model of communication protocol, in which each layer performs a specific task. The purpose of this model is to make all kinds of hardware communicate with each other at the same level. These seven layers are: physical layer, data link layer, network layer, transport layer, session layer, presentation layer and application layer. The TCP / IP communication protocol adopts a four layer hierarchical structure, and each layer calls the network provided by its next layer to fulfill its own requirements. These four layers are:
application layer: the layer of communication between applications, such as simple e-mail transfer (SMTP), file transfer protocol (FTP), network remote access protocol (telnet), etc
transport layer: in this layer, it provides data transmission services between nodes, such as transmission control protocol (TCP), user datagram protocol (UDP), etc. TCP and UDP add transmission data to the packet and transmit it to the next layer, which is responsible for transmitting data and determining that the data has been delivered and received<
interconnection network layer: it is responsible for providing basic packet transmission function, so that each packet can reach the destination host (but not check whether it is received correctly), such as Internet Protocol (IP)
network interface layer: the management of the actual network media, defining how to use the actual network (such as Ethernet, serial line, etc.) to transmit data<
protocols in TCP / IP
the following is a brief introction to the functions of the protocols in TCP / IP and how they work:
1. IP
IP is the heart of TCP / IP and the most important protocol in the network layer
the IP layer receives the packets sent by the lower layer (network interface layer, such as Ethernet device driver), and sends the packets to the higher layer TCP or UDP layer; On the contrary, IP layer also transfers packets received from TCP or UDP layer to lower layer. IP packets are unreliable because IP doesn't do anything to confirm that the packets are sent in order or are not corrupted. IP packet contains the address of the host sending it (source address) and the address of the host receiving it (destination address)
when receiving packets, TCP and UDP services usually assume that the source address in the packet is valid. It can also be said that IP addresses form the authentication basis of many services, which believe that packets are sent from a valid host. IP confirmation contains an option called IP source routing, which can be used to specify a direct path between the source address and the destination address. For some TCP and UDP services, IP packets using this option seem to be delivered from the last system on the path rather than from its real location. This option exists for testing purposes, indicating that it can be used to spoof the system to make normally forbidden connections. Then, many services that rely on IP source address for confirmation will have problems and will be illegally intruded
2. TCP
if there are sealed TCP packets in IP packets, then IP will "up" them to the TCP layer. TCP sorts packets and checks for errors, and realizes the connection between virtual circuits. TCP packets include sequence number and acknowledgement, so packets not received in order can be sorted, while damaged packets can be retransmitted
TCP sends its information to higher-level applications, such as telnet's service program and client program. Applications send information back to the TCP layer in turn, and the TCP layer sends them down to the IP layer, device drivers and physical media, and finally to the receiver
connection oriented services (such as Telnet, FTP, rlogin, X windows, and SMTP) require a high degree of reliability, so they use TCP. DNS uses TCP (send and receive domain name databases) in some cases, but uses UDP to send information about a single host
3. UDP
UDP and TCP are in the same layer, but the order of packets is wrong or retransmitted. Therefore, UDP is not used for connection oriented services that use virtual circuits. UDP is mainly used for query response oriented services, such as NFS. Compared with FTP or Telnet, these services need to exchange less information. Services that use UDP include NTP (network down time protocol) and DNS (DNS also uses TCP)
spoofing UDP packets is easier than spoofing TCP packets, because UDP does not establish an initial connection (also known as handshake) (because there is no virtual circuit between the two systems), that is to say, UDP related services face greater risks< ICMP
4. ICMP is located in the same layer as IP, which is used to transmit IP control information. It is mainly used to provide information about the path to the destination address. ICMP's "redirect" information informs the host of a more accurate path to other systems, while the "unreachable" information indicates that there is a problem with the path. In addition, if the path is not available, ICMP can terminate the TCP connection "gracefully". Ping is the most commonly used ICMP based service
5. Port structure of TCP and UDP
TCP and UDP services usually have a client / server relationship. For example, a telnet service process starts to be idle on the system, waiting for connection. The user uses the telnet client to establish a connection with the service process. The client program writes information to the service process, the service process reads the information and sends a response, and the client program reads the response and reports it to the user. Therefore, the connection is plex and can be used for reading and writing
How do multiple telnet connections between two systems confirm and coordinate with each other? The TCP or UDP connection uniquely uses the following four items in each message to confirm:
source IP address the IP address of the sending packet
destination IP address the IP address of the received packet
source port the port of the connection on the source system
destination port the port of the connection on the destination system
port is a software structure, which is used by client program or service process to send and receive information. A port corresponds to a 16 bit number. Service process usually uses a fixed port, for example, SMTP uses 25, xwindows uses 6000. These port numbers are "well known" because these addresses and destination addresses are needed to communicate when establishing a connection to a particular host or service
communication protocol of TCP / IP
this part briefly introces the internal structure of TCP / IP, so as to lay a foundation for the discussion of Internet related security issues. TCP / IP protocol group is popular in part because it can be used on a variety of channels and underlying protocols (such as T1 and X.25, Ethernet and RS-232 serial interface). To be exact, TCP / IP protocol is a group of protocols including TCP protocol and IP protocol, UDP (User Datagram Protocol), ICMP (Internet control message protocol) and other protocols<
overview of the overall architecture of TCP / IP
TCP / IP protocol does not fully conform to the seven layer reference model of OSI. The traditional open system interconnection reference model is a seven layer abstract reference model of communication protocol, in which each layer performs a specific task. The purpose of this model is to make all kinds of hardware communicate with each other at the same level. These seven layers are: physical layer, data link layer, network layer, transport layer, session layer, presentation layer and application layer. The TCP / IP communication protocol adopts a four layer hierarchical structure, and each layer calls the network provided by its next layer to fulfill its own requirements. These four layers are:
application layer: the layer of communication between applications, such as simple e-mail transfer (SMTP), file transfer protocol (FTP), network remote access protocol (telnet), etc
transport layer: in this layer, it provides data transmission services between nodes, such as transmission control protocol (TCP), user datagram protocol (UDP), etc. TCP and UDP add transmission data to the packet and transmit it to the next layer, which is responsible for transmitting data and determining that the data has been delivered and received<
interconnection network layer: it is responsible for providing basic packet transmission function, so that each packet can reach the destination host (but not check whether it is received correctly), such as Internet Protocol (IP)
network interface layer: the management of the actual network media, defining how to use the actual network (such as Ethernet, serial line, etc.) to transmit data<
protocols in TCP / IP
the following is a brief introction to the functions of the protocols in TCP / IP and how they work:
1. IP
IP is the heart of TCP / IP and the most important protocol in the network layer
the IP layer receives the packets sent by the lower layer (network interface layer, such as Ethernet device driver), and sends the packets to the higher layer TCP or UDP layer; On the contrary, IP layer also transfers packets received from TCP or UDP layer to lower layer. IP packets are unreliable because IP doesn't do anything to confirm that the packets are sent in order or are not corrupted. IP packet contains the address of the host sending it (source address) and the address of the host receiving it (destination address)
when receiving packets, TCP and UDP services usually assume that the source address in the packet is valid. It can also be said that IP addresses form the authentication basis of many services, which believe that packets are sent from a valid host. IP confirmation contains an option called IP source routing, which can be used to specify a direct path between the source address and the destination address. For some TCP and UDP services, IP packets using this option seem to be delivered from the last system on the path rather than from its real location. This option exists for testing purposes, indicating that it can be used to spoof the system to make normally forbidden connections. Then, many services that rely on IP source address for confirmation will have problems and will be illegally intruded
2. TCP
if there are sealed TCP packets in IP packets, then IP will "up" them to the TCP layer. TCP sorts packets and checks for errors, and realizes the connection between virtual circuits. TCP packets include sequence number and acknowledgement, so packets not received in order can be sorted, while damaged packets can be retransmitted
TCP sends its information to higher-level applications, such as telnet's service program and client program. Applications send information back to the TCP layer in turn, and the TCP layer sends them down to the IP layer, device drivers and physical media, and finally to the receiver
connection oriented services (such as Telnet, FTP, rlogin, X windows, and SMTP) require a high degree of reliability, so they use TCP. DNS uses TCP (send and receive domain name databases) in some cases, but uses UDP to send information about a single host
3. UDP
UDP and TCP are in the same layer, but the order of packets is wrong or retransmitted. Therefore, UDP is not used for connection oriented services that use virtual circuits. UDP is mainly used for query response oriented services, such as NFS. Compared with FTP or Telnet, these services need to exchange less information. Services that use UDP include NTP (network down time protocol) and DNS (DNS also uses TCP)
spoofing UDP packets is easier than spoofing TCP packets, because UDP does not establish an initial connection (also known as handshake) (because there is no virtual circuit between the two systems), that is to say, UDP related services face greater risks< ICMP
4. ICMP is located in the same layer as IP, which is used to transmit IP control information. It is mainly used to provide information about the path to the destination address. ICMP's "redirect" information informs the host of a more accurate path to other systems, while the "unreachable" information indicates that there is a problem with the path. In addition, if the path is not available, ICMP can terminate the TCP connection "gracefully". Ping is the most commonly used ICMP based service
5. Port structure of TCP and UDP
TCP and UDP services usually have a client / server relationship. For example, a telnet service process starts to be idle on the system, waiting for connection. The user uses the telnet client to establish a connection with the service process. The client program writes information to the service process, the service process reads the information and sends a response, and the client program reads the response and reports it to the user. Therefore, the connection is plex and can be used for reading and writing
How do multiple telnet connections between two systems confirm and coordinate with each other? The TCP or UDP connection uniquely uses the following four items in each message to confirm:
source IP address the IP address of the sending packet
destination IP address the IP address of the received packet
source port the port of the connection on the source system
destination port the port of the connection on the destination system
port is a software structure, which is used by client program or service process to send and receive information. A port corresponds to a 16 bit number. Service process usually uses a fixed port, for example, SMTP uses 25, xwindows uses 6000. These port numbers are "well known" because these addresses and destination addresses are needed to communicate when establishing a connection to a particular host or service
7. The abbreviation of transmission control protocol / Internet protocol, which is translated into Chinese as transmission control protocol / Internet Interconnection Protocol, also known as network communication protocol, is the most basic protocol of Internet and the foundation of Internet. It is composed of IP protocol of network layer and TCP protocol of transmission layer. TCP / IP defines how electronic devices connect to the Internet and how data is transmitted between them. The protocol adopts a four layer hierarchical structure, and each layer calls the protocol provided by its next layer to fulfill its own requirements. Generally speaking: TCP is responsible for finding the problem of transmission. When there is a problem, it will send out a signal to request retransmission until all data is safely and correctly transmitted to the destination. IP is an address for every computer on the Internet< br />
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8. Ha ha, forget it. I'll give you an answer when I'm free
1. Whether the IP of these three devices is randomly assigned by telecom depends on whether you pull the optical fiber or PPPoE dial-up Internet access. If you pull the optical fiber, it is the fixed IP. If you are broadband dial-up Internet access, the external IP is randomly assigned. You have a mistake about the port. The TCP / IP port is not assigned by the router, but the port used by the process on your computer
2; B\ C devices go online and use the same external IP.
1. Whether the IP of these three devices is randomly assigned by telecom depends on whether you pull the optical fiber or PPPoE dial-up Internet access. If you pull the optical fiber, it is the fixed IP. If you are broadband dial-up Internet access, the external IP is randomly assigned. You have a mistake about the port. The TCP / IP port is not assigned by the router, but the port used by the process on your computer
2; B\ C devices go online and use the same external IP.
9. TCP is a connection oriented communication protocol. The connection is established through three handshakes. When the communication is completed, the connection must be removed. Because TCP is connection oriented, it can only be used for end-to-end communication
TCP provides a reliable data stream service, which uses "positive acknowledgement with retransmission" technology to achieve the reliability of transmission. TCP also uses a method called "sliding window" to control the flow. The so-called window actually represents the receiving ability, which is used to limit the sending speed of the sender.
TCP provides a reliable data stream service, which uses "positive acknowledgement with retransmission" technology to achieve the reliability of transmission. TCP also uses a method called "sliding window" to control the flow. The so-called window actually represents the receiving ability, which is used to limit the sending speed of the sender.
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