CSMA/CD 载波侦听，多路访问，冲突，冲突检测(回退算法)
CSMA/CD stands for Carrier Sense Multiple Access/Collision Detection. It is a media access control method used in Ethernet networks. In CSMA/CD, multiple devices share a common communication channel, and each device listens to the channel before transmitting data. If a device detects another transmission on the channel, it waits for a random period of time before attempting to transmit again.
If two devices transmit data simultaneously and a collision occurs, the devices detect the collision and stop transmitting. They then wait for a random period of time before attempting to transmit again. This process of detecting collisions and retransmitting data is known as collision detection.
CSMA/CD is used in half-duplex Ethernet networks where multiple devices share a single communication channel. In full-duplex Ethernet networks, collision detection is not required, as each device has its own dedicated transmit and receive channels.
frame structure of ethernet
Ethernet is a widely used networking technology that uses frames to transmit data over a network. The frame structure of Ethernet consists of the following components:
Preamble: The preamble is a sequence of 7 bytes (56 bits) that precedes the frame. It is used to signal the start of the frame and to synchronize the clocks of the sender and receiver.
Start Frame Delimiter (SFD): The SFD is a single byte (8 bits) that marks the end of the preamble and the beginning of the frame.
Destination Address: The destination address field is a 6-byte (48-bit) field that specifies the MAC address of the destination device.
Source Address: The source address field is a 6-byte (48-bit) field that specifies the MAC address of the sender.
Length/Type: The Length/Type field is a 2-byte (16-bit) field that specifies either the length of the data field or the type of protocol being used.
Data: The Data field is a variable length field that contains the actual data being transmitted.
Frame Check Sequence (FCS): The FCS is a 4-byte (32-bit) field that is used to verify the integrity of the data being transmitted.
The Ethernet frame structure can vary depending on the specific type of Ethernet being used. For example, in the case of IEEE 802.3 Ethernet, the Length/Type field is used to indicate the length of the data field, while in the case of IEEE 802.2 Ethernet, the Length/Type field is used to indicate the type of protocol being used.
communication types among LAN
单播，组播，广播
There are three main types of communication that can occur among devices on a Local Area Network (LAN):
Unicast: Unicast communication involves a single sender and a single receiver. In this type of communication, the sender sends a message to a specific device on the network, and only that device receives and processes the message.
Multicast: Multicast communication involves a single sender and multiple receivers. In this type of communication, the sender sends a message to a specific group of devices on the network, and all devices that are part of that group receive and process the message.
Broadcast: Broadcast communication involves a single sender and all devices on the network. In this type of communication, the sender sends a message to every device on the network, and all devices receive and process the message.
The choice of communication type depends on the specific requirements of the application or service being used on the network. For example, unicast communication is commonly used for peer-to-peer file sharing or for sending messages to a specific device, while multicast communication is often used for streaming video or audio content to a group of devices. Broadcast communication is typically used for network discovery or for sending important notifications to all devices on the network.
how many bits of a mac address
A MAC address is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within a network segment.
A MAC address is 48 bits long, represented in hexadecimal format with each byte separated by a colon or a hyphen. The first 24 bits (first 3 bytes) of a MAC address identify the manufacturer of the NIC, while the last 24 bits (last 3 bytes) are unique to the device itself.
Yes, that's correct. The first 24 bits (3 bytes) of a MAC address represent the Organizationally Unique Identifier (OUI), which identifies the manufacturer or vendor of the network interface card (NIC). The remaining 24 bits (3 bytes) are used to identify the specific device, and are assigned by the manufacturer.
The OUI is assigned by the Institute of Electrical and Electronics Engineers (IEEE), which is responsible for maintaining the global registry of MAC addresses. This helps to ensure that each MAC address is unique and avoids conflicts between devices on a network.
48bits, 6个byte。
90-0F-0C-45-EE-DB
MAC地址查询 - 90-0F-0C - 在线工具 (itool.co)
RJ-45 connector
RJ-45 (Registered Jack-45) is a type of connector commonly used for Ethernet network cables. It has eight pins and is used to connect twisted pair cables, such as Cat5, Cat5e, and Cat6, to network devices such as switches, routers, and computers. The connector is similar in appearance to a standard phone jack, but has more pins and a wider body. RJ-45 connectors can be either shielded or unshielded, with shielded connectors providing better protection against electromagnetic interference. The connectors can be crimped onto the end of the cable using a specialized tool.
以太网使用双绞线作为物理介质。要求使用的双绞线必须符合特定的技术规范，包括线材的直径、颜色编码、长度等。常见的双绞线规范有以下几种：
Cat5双绞线：这是最常见的双绞线类型之一，支持传输速率高达100Mbps。
Cat5e双绞线：这种双绞线规范支持传输速率高达1Gbps，是一种更高效的选择。
Cat6双绞线：这种双绞线规范支持传输速率高达10Gbps，是一种最新的高速传输技术。
另外，以太网使用的双绞线要求有正确的接头和连接器，如RJ-45连接器，以保证良好的信号质量和连接稳定性。还需要使用合适的物理介质转换器和延长器，以支持跨越不同类型的网络介质和设备之间的连接。
EIA/TIA T56A communicate EIA/TIA T56B, explain in English
EIA/TIA T568A and T568B are two different wiring standards used for terminating Ethernet cables. T568A and T568B both define the pinout (i.e., the order in which the wires are connected to the pins) for terminating eight-wire twisted pair copper cables.
Both standards are compatible and can be used to make Ethernet connections, as long as both ends of the cable are terminated with the same standard. This means that a T568A terminated cable can only be connected to another T568A terminated cable or to a device that follows the T568A wiring standard. Similarly, a T568B terminated cable can only be connected to another T568B terminated cable or to a device that follows the T568B wiring standard.
UTP-实现 直通与交叉， explain in English
UTP cables can be wired as either straight-through or crossover cables.
A straight-through cable is used to connect devices of different types, such as a computer to a switch or a router to a modem. In a straight-through cable, the wire connections at one end of the cable are the same as the connections at the other end.
On the other hand, a crossover cable is used to connect devices of the same type, such as two computers or two switches. In a crossover cable, the wire connections at one end of the cable are reversed from the connections at the other end. For example, the transmit wires at one end are connected to the receive wires at the other end, and vice versa.
UTP（Unshielded Twisted Pair，无屏蔽双绞线）是一种常见的局域网传输介质，常用于以太网。在使用UTP线缆时，需要实现直通和交叉两种线序。
直通线是指在一端用1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8的顺序连接到另一端。直通线常用于将计算机与交换机、路由器等设备连接。
交叉线是指将一端的1-2, 2-3, 3-6, 4-5线序调换到另一端的3-6, 1-2, 2-3, 4-5上。交叉线常用于将两台计算机直接连接，实现文件共享、网络打印等功能。
为了便于识别，直通线一般采用绿色或灰色外壳，交叉线则采用橙色或红色外壳。
The maximum length of an Ethernet cable depends on the type of Ethernet being used and the transmission speed. Here are the maximum cable lengths for some common Ethernet standards:
10BASE-T (Ethernet): 100 meters (328 feet)
100BASE-TX (Fast Ethernet): 100 meters (328 feet)
1000BASE-T (Gigabit Ethernet): 100 meters (328 feet)
10GBASE-T (10 Gigabit Ethernet): 100 meters (328 feet)
It's important to note that these cable lengths are for a single cable segment without any repeaters or other network devices in between. If you need to extend the network beyond the maximum cable length, you can use a repeater or switch to regenerate the signal and extend the range.
交换机分隔冲突域的，路由器分隔广播域的。
fping is a command-line utility used to ping multiple hosts at once. It is similar to the traditional ping utility but allows for sending pings to a group of hosts instead of just one host at a time. The output of fping can be used for network troubleshooting and monitoring purposes. It is available for various operating systems including Linux, Windows, and macOS.
Arpspoof is a command-line tool used to perform an ARP spoofing attack. ARP spoofing is a type of attack where an attacker sends fake Address Resolution Protocol (ARP) messages on a local area network (LAN) to link the attacker's MAC address with the IP address of another device on the network. This allows the attacker to intercept, modify, or even stop the communication between the two devices. Arpspoof is often used as a tool for network testing, but it can also be used maliciously in a network attack.
fping and arpspoof are not recognized on win10
Both fping and arpspoof are command-line utilities typically used in Linux and Unix-like operating systems. They may not be recognized on Windows 10 by default as they are not built-in Windows utilities.
To use these utilities on Windows 10, you need to install them manually. One way to do this is to install a Unix-like environment on Windows, such as Cygwin, which provides a set of Linux/Unix-like utilities and tools that can be used on Windows. Another way is to use a virtual machine with a Linux or Unix-like operating system installed.
Alternatively, you can use Windows alternatives to these utilities, such as ping for fping and ARPing for arpspoof. These utilities are built-in to Windows and can be run from the command prompt or PowerShell.
Arp spoofing or ARP poisoning is a type of attack that involves falsifying ARP messages on a LAN in order to associate the attacker's MAC address with the IP address of another host on the network. This can allow the attacker to intercept network traffic, launch a man-in-the-middle attack, or steal sensitive information.
There are several ways to detect ARP attacks:
Monitor ARP cache: By monitoring the ARP cache on your computer or router, you can detect if there are multiple MAC addresses associated with the same IP address. This can indicate an ARP spoofing attack.
Use ARPwatch: ARPwatch is a tool that monitors ARP activity on a network and can alert you to any changes in the ARP table. It can also be configured to send email alerts when suspicious activity is detected.
Use a network intrusion detection system: Network intrusion detection systems (NIDS) can detect ARP spoofing attacks by analyzing network traffic for unusual patterns or anomalies. There are several open-source and commercial NIDS solutions available.
Use static ARP entries: By configuring static ARP entries on your computer or router, you can prevent ARP spoofing attacks by ensuring that only the authorized MAC address is associated with a particular IP address.
It's important to note that ARP attacks can be difficult to detect, especially if they are carried out by a skilled attacker. Implementing good network security practices, such as using strong passwords and encryption, can also help protect against ARP attacks.
Will the device send arp broadcast periodically?
No, devices typically only send ARP broadcasts when they need to resolve the MAC address of a particular IP address, such as when sending a packet to a device on a different subnet or when the MAC address of a device is not already in the ARP cache. The device will then update its ARP cache with the MAC address it receives in response to the broadcast. The frequency of ARP broadcasts will depend on the network traffic and the frequency of devices joining or leaving the network.
driftnet 嗅探工具
Driftnet watches network traffic, and picks out and displays JPEG and GIF images for display.
Driftnet is a network tool that captures and displays images transferred over a network. It is commonly used as a security tool to monitor network traffic and detect any inappropriate use of images or visual content.
Driftnet operates by capturing and analyzing network traffic in real-time, and identifying and extracting any images that are being transferred over the network. The captured images are then displayed in a graphical user interface, allowing the user to view the images and determine if they are appropriate or not.
Driftnet can be used to monitor any network interface and can capture images from a wide variety of protocols, including HTTP, FTP, and SMTP. It is often used by security professionals and network administrators to monitor network activity and detect any unauthorized use of visual content.
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