TCP/IP BASICS (I), tcpip Basics

TCP/IP BASICS (I), tcpip Basics

1. Architecture and main protocols of TCP/IP protocol family

The TCP/IP protocol family is a layer-4 protocol system.

Data link layer: implements network drivers for Nic interfaces to process data transmission on physical media (such as Ethernet and Token network. The two common protocols on the data link layer are ARP (Address Resolve Protocol) and RARP (Revers Address Resovle Protocol ). Converts IP addresses to physical addresses.

Network Layer: select and forward data packets. The network layer has two major protocols: the IP Protocol (Internet Protocol) and the ICMP Protocol (Internet Control Message Protocol). The IP Protocol is the core.

Transport Layer: Provides end-to-end communication for applications on two hosts. The transport layer has three main Protocols: TCP, UDP, and SCTP.

Application Layer: responsible for processing application logic. The application layer is mainly implemented in user space and is responsible for processing a large number of logics, such as file, name query, and network management.

Ii. Encapsulation

Before an application is sent to a physical network, it is transmitted from top to bottom along the protocol stack.

The data encapsulated by TCP is called a TCP packet segment. There are also UDP datagram and IP datagram. The data encapsulated by the data link layer is called a frame ).

An Ethernet frame uses a 6-byte physical address and a 6-byte source physical address to represent both Parties to the communication.

Frames are the sequence of bytes that are finally transmitted over the physical network.

Iii. Sub-Use

When the frame arrives at the target host, it is transferred from the bottom to the top of the protocol stack. The use of this function depends on the Type field in the header information.

The IP protocol, ARP protocol, and RARP protocol are both frame transmission data. The header of the frame needs fields to distinguish them. For example, the value of the Ethernet frame field type is:

0x8000, the data part of the frame is IP datagram, And the Ethernet Program delivers the frame to the IP module.

0x806 indicates the ARP request or response packet.

0x835, which is the RARP request or response program.

After the frame is used, the original data before encapsulation is finally sent to the target service.

Iv. Port

Well-known ports: from 0 to 1023, which are allocated and controlled by IANA and bound to some services.

Registered Ports (Registered Ports): from 1024 to 49151. These Ports are not controlled by IANA, but are Registered by IANA and provide a usage list. For example, 1433 Microsoft SQL server port.

Dynamic or Private Ports: From 49152 to 65535. IANA regardless of these Ports.

What is the TCP/IP group?

TCP/IP Protocol Introduction

TCP/IP communication protocol

This section briefly introduces the internal structure of TCP/IP and lays the foundation for discussing Internet-related security issues. TCP/IP protocol groups are popular in part because they can be used on a variety of channels and underlying protocols (such as T1 and X.25, Ethernet, and RS-232 serial interfaces. Specifically, TCP/IP is a set of protocols, including TCP and IP, UDP (User datainprotocol), and ICMP (Internet Control Message Protocol) protocol and other protocol groups.

Overview of TCP/IP architecture

The TCP/IP protocol does not fully comply with the OSI Layer-7 Reference Model. The traditional Open System Interconnection Reference Model is a layer-7 abstract reference model of communication protocols, where each layer executes a specific task. This model aims to make various hardware communicate with each other at the same level. These seven layers are: physical layer, data link layer, network layer, transmission layer, voice layer, presentation layer and application layer. The TCP/IP communication protocol uses a layer-4 hierarchy. Each layer calls the network provided by its next layer to meet its own needs. The four layers are:

Application Layer: layer for communications between applications, such as simple Email transmission (SMTP), file transfer protocol (FTP), and network remote access protocol (Telnet.

Transport Layer: In this layer, it provides data transmission services between nodes, such as transmission control protocol (TCP) and User Datagram Protocol (UDP, TCP and UDP add transmitted data to the data packet and transmit it to the next layer. This layer is responsible for transmitting data and confirming that the data has been delivered and received.

Interconnect Network Layer: provides basic data packet transmission functions so that each data packet can reach the target host (but does not check whether it is correctly received), such as Internet Protocol (IP ).

Network Interface Layer: manages the actual network media and defines how to transmit data using the actual network (such as Ethernet and Serial Line.

Protocols in TCP/IP

The following is a brief introduction of what functions are available in TCP/IP protocols and how they work:

1. IP

Internet Protocol IP is the heart of TCP/IP and the most important protocol in the network layer.

The IP layer receives a packet from a lower layer (network interface layer, such as an Ethernet device driver) and sends the packet to a higher layer-TCP or UDP layer, the IP layer also sends packets received from the TCP or UDP layer to the lower layer. IP packets are unreliable because the IP does not do anything to confirm that the packets are sent in order or are not damaged. An IP packet contains the address (source address) of the host that sent the packet and the address (Destination Address) of the host that received the packet ).

When receiving data packets, high-level TCP and UDP services generally assume that the source address in the packet is valid. It can also be said that IP addresses form the authentication basis for many services. These services believe that data packets are sent from a valid host. IP validation 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, the IP packet with this option is transmitted from the last System in the path, rather than from its actual location. This option exists for testing, indicating that it can be used to fool the system for a normally prohibited connection. Therefore, many services that rely on the IP Source Address for confirmation will have problems and will be illegally infiltrated.

2. TCP

If an IP packet contains a TCP packet that has been blocked, the IP will send them to the upper layer. TCP sorts packets and checks errors to connect virtual circuits. TCP packets include serial numbers and validation, so packets not received in order can be sorted, and damaged packets can be re-transmitted.

TCP sends its information to higher-level applications, such as Telnet service programs and customer programs. The application takes turns to take the rest of the full text...>

What is the basis for TCP/IP explanation? The knowledge in this article is becoming increasingly incomprehensible.

TCP/IP volume is a good book. We recommend that you read this book systematically after you finish learning CCNA or CCNP.
If you are new to the Internet, this book will certainly be difficult to read.