Shulou(Shulou.com)06/01 Report--

2.1 Network Interconnection Foundation

Collision domain: each network segment connected to the switch is a separate collision domain

The reasons why LAN traffic is blocking the network:

1. Too many hosts are installed in a broadcast domain or conflict domain

2. Broadcast storm

3. Excessive multicast traffic

4. Low bandwidth

5. Use hubs in the network

Hub: only responsible for connecting network segments, and will not split network segments. For home networks only

Router: by default, the broadcast domain is isolated and links to WAN services are provided. The router uses a serial interface to provide WAN connectivity.

Advantages:

1. Do not forward broadcasts by default

2. Network traffic can be filtered according to the third layer (network layer) information.

Features:

1. Packet exchange

2. Packet filtering

3. Internet communication

4. Path selection

Internet: a router provides packet filtering through an access list. When a router connects two or more networks together, it uses logical addressing technology (IP or IPV6), which is called the Internet.

Switch: add network LAN function to divide collision domain (each port of the switch is a collision domain) responsible for forwarding or filtering data frames

Features:

1. Optimize LAN work

2. Optimize the performance of LAN

3. Provide more bandwidth for LAN users

# Bridge refers to the previous switch, which works basically the same as the switch!

2.2.1 hierarchical model:

It solves all the processes required for effective communication and logically classifies these processes into layers

2.3OSI reference model

One of the most important functions is to solve the data transmission between different hosts.

OSI has seven layers and is divided into two groups

The upper three layers define how applications of terminal workstations communicate with each other and how to communicate with users.

Application layer: provide user interface

Presentation layer: represents processes such as data management encryption

Session layer: independently manage the processes of different applications

# the role of the upper layer is to realize the communication between the application and the host

# the lower four layers define how to transmit data through physical cables or through switches and routers, and how to re-establish the connection between the application of the transmission host and the destination host

Transport layer: provides reliable or unreliable transmission to perform error correction before transmission

Network layer: provides logical addressing routers use logical addresses to determine the transmission path

Data link layer: turns packets into bytes and bytes into data frames using MAC addresses to provide media access for error detection without error correction

Physical layer: transmits bits between devices to determine the voltage, line rate, and transmission pins on the cable

# the following devices work on the "all" layer 7 of the OSI model:

Network management station [NMS]

Web and Application Server

Gateway (not the default gateway)

Network host

Application layer: (Application Layer)

In fact, where the communication between the user and the computer is handled, the application layer is the interface of the actual application, and the next layer of the application layer sends the application information down to the protocol stack.

Responsible for identifying and establishing the possibility of communication between the parties who intend to establish communication, and determining whether there are sufficient resources to support communication between the two parties

Presentation layer (Presentation)

Presents the data to the application layer and is responsible for providing the data conversion and encoding format. Essentially a converter defines a standard data format associated with data compression, decompression, encryption, and decryption. The presentation layer standard also involves media services.

Session layer (Session Layer)

Responsible for establishing, managing and dismantling the dialogue between the presentation layer, providing the session control function between the device meeting nodes

# three modes are used to manage communications:

Simplex (Simplex)

Half-duplex (Half Duplex)

Full duplex (Full Duplex)

Distinguish the data of different applications from the data of other applications

Transport layer (Transport Layer)

Segment and combine the data in higher-level applications, and put the data into the same data flow to provide end-to-end data transmission services, in the network, establish a logical connection transport layer provides a mechanism to reuse the higher layer should establish a session and remove the virtual line to hide all the details of network-related information from the higher layer, thus providing transparent transmission

# reliable network communication can be used at the transport layer, which means that this protocol uses acknowledgement, sorting and flow control mechanisms.

# the transport layer can be connectionless or connection-oriented. Understand connection orientation in Cisco:

Flow control:

Flow control prevents the sending host at one end of the connection from overflowing the reception of the receiving host-a situation that can lead to packet loss

Connection-oriented communication:

In a reliable transmission operation, the device that transmits the data establishes a call: establishes a connection-oriented communication session

This behavior becomes:

Call connection or three-way handshake (the process of creating this virtual line becomes an overhead)

Cause of blockage:

The speed of data stream generated by computer is faster than that of network processing and transmission.

Connection-oriented service features:

Establish a virtual link

Use the sequence mechanism

Use the confirmation mechanism

Use flow control

Flow control mechanism:

Caching

Sliding window

Congestion avoidance

Slide the window:

Before receiving the confirmation message, the number of data segments that the transmission device can send becomes a window.

Responsible for controlling the number of unacknowledged packet segments

Confirmation mechanism:

A reliable data transmission mechanism ensures the integrity of the data and ensures that the data flow will not be repeated or lost, which is guaranteed by an active confirmation mechanism with retransmission function.

Network layer:

Manage device addressing, track the location of the device in the network, and be responsible for determining the best path to transmit data

The network layer uses two packet types:

Data packets: the protocol used to support data traffic is called the routed protocol (a protocol that defines the format of fields in a Datagram and provides a mechanism for user communication transmission)

Routing update packet: used to update the information of neighboring routers, and the protocol used to send routing update packets becomes a routing protocol. Routing update packets are used to help build and maintain routing tables on each router

The routing table contains:

Network address: related to the protocol. Routers must maintain separate routing tables for each routed protocol, because different routed protocols use completely different addressing mechanisms to build the network topology

Interface: the exit used by the packet

Metric: the distance to the remote network

Data Link layer:

Responsible for providing physical transmission of data, handling error notifications, network topology, and implementing flow control

It is responsible for converting messages from the network layer into bit formats for transmission at the physical layer.

IEEE defines the Ethernet data link layer as two layers:

Media access Control (MAC) 802.3: defines how packets are placed in the media

Logical Link Control (LLC) 802.2: responsible for identifying network layer protocols and encapsulating them.

The LLC header is responsible for telling the data link layer what to do with a data frame after it is received

Physical layer:

Send bits and receive bits, different media types will express these bits in different ways.

Defines all electrical, mechanical, procedural and functional requirements for activating, maintaining, and closing physical links between two end systems

Responsible for distinguishing DTE (data terminal equipment) and DCE (data communication equipment) interfaces. The DCE is usually located at the operator, and the DTE is the device connected to it

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