Vro with network Basics

Vro is the main node device on the Internet. The router determines data forwarding through routing. A forwarding rule is called routing, which is also the origin of the router name (router, forwarder ). As a hub connecting different networks, the router system forms the main context of the TCP/IP-based Internet. It can also be said that the router forms the backbone of the Internet. The processing speed is one of the major bottlenecks of network communication. Its Reliability directly affects the quality of network interconnection. Therefore, in the field of campus network, Regional Network, and even Internet research, router technology is always at the core position, and its development history and direction have become a microcosm of Internet research. As China's network infrastructure and information construction are in the ascendant, we will discuss the role, position, and development direction of routers in the interconnected networks, it is of great significance to clarify the plausible concepts of vrouters and network interconnection in the network market.

Vro Functions

One role of a router is to connect different networks, and the other is to select the information transmission line. Selecting smooth and fast routes can greatly improve the communication speed, reduce the communication load of the network system, save network system resources, and improve the network system accessibility rate, so that the network system can exert greater benefits.

From the perspective of filtering network traffic, the role of a router is very similar to that of a switch and a bridge. However, unlike switches that work on the physical layer and divide network segments physically, vrouters use specialized software protocols to logically divide the entire network. For example, a router that supports the IP protocol can divide the network into multiple sub-network segments. Only network traffic directed to a Special IP Address can pass through the router. For each received packet, the router recalculates its verification value and writes it to a new physical address. Therefore, the speed of data forwarding and filtering by vro is usually slower than that of A vswitch that only views the physical address of a data packet. However, vrouters can improve the overall efficiency of networks with complex structures. Another obvious advantage of a vro is that it can automatically filter network broadcasts. In general, the installation process of adding a vro to a network is much more complex than that of a plug-and-play vswitch.

Generally, a vro should be used to connect a heterogeneous network to multiple subnets.

The main task of a router is to find an optimal transmission path for each data frame passing through the router and transmit the data to the destination site effectively. It can be seen that the routing algorithm is the key to selecting the optimal path. To achieve this, the route Table is stored in the router for Routing selection. The path table contains the subnet flag information, the number of online routers, and the name of the next router. The path table can be set by the system administrator or dynamically modified by the system. It can be automatically adjusted by the router or controlled by the host.

1. Static path table

The system administrator sets a fixed path table in advance, which is called a static path table. It is generally set in advance according to the network configuration during system installation, it will not change as the network structure changes in the future.

2. Dynamic Path table

The Dynamic (Dynamic) path table is the path table automatically adjusted by the router according to the running status of the network system. The router automatically learns and remembers network running conditions based on the functions provided by the Routing selection Protocol (Routing Protocol), and automatically calculates the optimal data transmission path as needed.

Vro Structure

Router Architecture

From the perspective of architecture, routers can be divided into the first generation single-CPU Single-structure router, the second generation single-bus master-slave CPU Structure router, and the third generation single-bus symmetric multi-CPU Structure router; the fourth generation multi-bus multi-CPU Structure router, the fifth generation shared-memory structure router, the sixth generation cross-Switch Architecture router, and the vro Based on the cluster system.

Router Composition

A vro has four elements: the input port, the output port, the switch, and the route processor.

The input port is the entrance of the physical link and input package. A port is usually provided by a line card. A line card generally supports 4, 8, or 16 ports. An input port has many functions. The first function is to encapsulate and deencapsulate the data link layer. The second function is to find the destination address of the input package in the forwarding table to determine the destination port (called route lookup). routing lookup can be implemented using common hardware, alternatively, you can embed a microprocessor into each line card. Third, to provide QoS (Service Quality), the port should divide the received packet into several predefined service levels. Fourth, ports may need to run data link-level protocols such as SLIP (Serial Line Internet Protocol) and PPP (Point-to-Point Protocol) or network-level protocols such as PPTP (Point-to-Point Tunneling Protocol. Once the route query is complete, you must use the switch to send the packet to its output port. If a router is added to a queue at the input end, several inputs share the same switch. In this way, the last function of the input port is to participate in the arbitration agreement for public resources (such as the switch.

The switch can be implemented using different technologies. So far, the most widely used switch technology is bus, cross switch and shared storage. The simplest switch uses a bus to connect all input and output ports. The disadvantage of the bus switch is that its switching capacity is limited by the capacity of the bus and the additional overhead for shared bus arbitration. The crossover switch provides multiple data paths through the switch. A crossover switch with N × N intersections can be considered to have 2N buses. If a crossover is closed, the data on the input bus is available on the output bus; otherwise, the data is unavailable. The scheduler controls the closing and opening of intersections. Therefore, the scheduler limits the switching speed. In the shared Storage Router, the incoming package is stored in the shared storage, and only the packet pointer is exchanged, which improves the switching capacity. However, the switch speed is limited by the storage device access speed. Although the storage capacity can double every 18 months, the storage access time is reduced by only 5% each year, which is an inherent limitation of the shared storage switch.

The output port stores packets before the packets are sent to the output link. complex scheduling algorithms can be implemented to support priorities and other requirements. Like the input port, the output port must also support encapsulation and encapsulation of the data link layer, as well as many advanced protocols.

The Route Processor calculates the forwarding table to implement the routing protocol and runs the software that configures and manages the router. At the same time, It also processes packages whose destination addresses are not in the wire adapter forwarding table.

Vro types can be seen everywhere in various levels of Internet networks. The access network allows families and small enterprises to connect to an Internet service provider. routers in the enterprise network connect to thousands of computers on a campus or enterprise. The router Terminal System on the backbone network is usually not accessible directly, they connect ISP and enterprise networks on the long-distance backbone network. The rapid development of the Internet poses different challenges to backbone networks, enterprise networks, and access networks. The backbone network requires the vro to be able to forward high-speed routes to a few links. Enterprise-level routers require a large number of ports and a low price. They also require easy configuration and QoS.

1. Access vro

Connect a vro to a small enterprise customer in a home or ISP. The Access Router does not only provide SLIP or PPP connections, but also supports VPC protocols such as PPTP and IPSec. These protocols must run on each port. Technologies such as ADSL will soon increase the available bandwidth of various families, which will further increase the burden on access routers. As a result of these trends, the Access Router will support many heterogeneous and high-speed ports in the future, and can run multiple protocols on each port, while also avoiding the telephone exchange network.

2. enterprise-level Routers

An enterprise or campus-level router connects to many terminal systems. Its main goal is to achieve as many endpoints as possible and further support different service quality. Many existing enterprise networks are Ethernet segments connected by hubs or bridges. Although these devices are cheap, easy to install, and do not require configuration, they do not support service levels. On the contrary, networks with vrouters can divide machines into multiple collision domains and thus control the size of a network. In addition, a vro supports a certain level of service and can be divided into at least multiple priority levels. However, the cost per port of the router is higher, and a lot of configuration work is required before it can be used. Therefore, the success or failure of an enterprise router lies in whether a large number of ports are provided, the cost per port is low, whether it is easy to configure, and whether QoS is supported. In addition, enterprise-level routers are required to effectively support broadcast and multicast. Enterprise networks also need to deal with various legacy LAN technologies and support multiple protocols, including IP, IPX, and Vine. They also support firewalls, packet filtering, and a large number of management and security policies and VLANs.

3. Backbone Router

Backbone routers enable enterprise-level network interconnection. The requirements for it are speed and reliability, and the cost is secondary. Hardware reliability can be achieved through technologies used in the telephone exchange network, such as hot backup, dual power supply, and dual data path. These technologies are almost standard for all backbone routers. The main performance bottleneck of a backbone IP router is the time it takes to find a route in the forwarding table. When a packet is received, enter the port in the forwarding table to find the destination address of the packet to determine its destination port. When the packet is shorter or the packet is sent to many destination ports, it is bound to increase the cost of Route Search. Therefore, placing some frequently accessed destination ports in the cache can improve the routing search efficiency. Whether it is an input buffer or an output buffer router, there is a bottleneck in route search. In addition to performance bottlenecks, the stability of routers is also a common concern.

4. Tbit Router

Fiber optic and DWDM are mature and ready-made among the three main technologies used by core internet in the future. If there is no router corresponding to the original bandwidth provided by the existing optical fiber technology and DWDM technology, the new network infrastructure will not be able to fundamentally improve the performance, therefore, developing high-performance backbone switches/routers (vrouters) has become an urgent requirement. The Tbit router technology is still in the development experiment stage.

Vro basic protocols and technologies

VPN

A VPN (Virtual Private Network) solution is an important feature of a router. The solution is roughly as follows:

1. Access Control

It is generally divided into PAP (Password Authentication Protocol) and CHAP (Advanced Password Authentication Protocol. PAP requires the hacker to provide the user name and password to the target router and allow the hacker to log on only when they match the information in the Access List. Although it provides a certain degree of security, user login information is not encrypted and easily stolen. CHAP came into being. It translates a random initial value with the user's original login information (username and password) by Hash algorithm to form a new login information. In this way, the user login information transmitted on the Internet is not transparent to hackers. Because the random initial values are different each time, the user's final login information will also be different, even if a user's login information is stolen, hackers cannot reuse the information. Note that due to the different Hash algorithms adopted by each vendor, CHAP is non-interoperable. To create a VPN, You need to place the same brand of routers on both sides of the VPN.

2. Data Encryption

In the encryption process, the number of encrypted bits is a very important parameter, which is directly related to the difficulty of decryption. Among them, Intel 9000 Series routers have the most outstanding performance, and are more than one hundred bits encrypted.

3. NAT (Network Address Translation-Network Address Translation protocol)

Like user login information, it is not safe to transmit IP addresses and MAC addresses without encryption on the Internet. NAT can translate valid IP addresses and MAC addresses into illegal IP addresses and MAC addresses for online transmission. After arriving at the target vro, it is translated into valid IP addresses and MAC addresses. This process is like CHAP, translation Algorithm vendors have different standards and cannot implement interoperability.

QoS

QoS (Quality of Service-Quality of Service) is a special term in Asynchronous Transmit Mode. QoS is not mentioned in IP addresses, however, the use of IP to transmit VOD and other multimedia information is increasingly used. As a packaged protocol, IP addresses seem to be unable to handle the problem: the delay is long and not a fixed value. packet loss leads to discontinuous and distorted signals. To solve these problems, the vendor provides several solutions: the first solution is based on the priority of different objects, and data packets sent by some devices (mostly multimedia applications) can be uploaded first. The second scheme is based on the protocol priority. You can define which Protocol has a higher priority. The protocol can be uploaded first. Both Intel and Cisco support this scheme. The third solution is to implement Multi-Link Point to Point Protocol (MLPPP). Cisco supports bandwidth aggregation by connecting multiple lines connected to two points to increase the bandwidth. The fourth solution is to reserve Resource RSVP (Resource Reservation Protocol), which distributes a portion of the bandwidth to multimedia signals. Other protocols are not allowed to occupy the bandwidth regardless of the congestion. These solutions can effectively improve the transmission quality.

RIP, OSPF, and BGP protocols

A large number of Routing protocols running on the Internet are RIP (Routing Information Protocol-Routing Information Protocol) and OSPF (Open Shortest Path First -- Open Shortest Path First) and BGP (Border Gateway Protocol-Border Gateway Protocol ). RIP and OSPF are internal gateway protocols and are applicable to the operation of unified routing protocols of a single ISP. A network operated by an ISP is called an autonomous system. BGP is a routing protocol between autonomous systems and an external gateway protocol.

RIP is the longest route protocol and the simplest route protocol. It mainly transmits route information (route table) to broadcast routes. Route tables are broadcast once every 30 seconds to maintain the relationship between neighboring routers, and their route tables are calculated based on the received route table. RIP is easy to run and applies to small networks. RIP is still used on the Internet.

OSPF protocol is short for "Open Shortest Path First. "Open" is for some manufacturers of "private" routing protocols at that time, and it is precisely because of the openness of the Protocol that makes OSPF powerful vitality and a wide range of uses. It obtains the network information by transmitting the link status (connection information), maintains a network directed topology, and uses the Minimum Spanning Tree Algorithm to obtain the route table. OSPF is a relatively complex routing protocol.

In general, OSPF and RIP are the internal routing protocols of autonomous systems and are suitable for a single ISP (Autonomous System. Generally, the entire Internet is not suitable for running a single routing protocol, because each ISP has its own interests and is unwilling to provide detailed routing information of its own network. To ensure the interests of various ISPs, the Standardization Organization has developed the BGP protocol between ISPs.

BGP processes route transmission between ISPs. It is characterized by a variety of routing policies, which cannot be achieved by RIP, OSPF, and other protocols, because they require global information to calculate the route table. BGP adds a certain policy to the router at the ISP border, selects a filter route, and sends routes such as RIP, OSPF, and BGP to the peer. The global and extensive Internet is an instance where BGP processes routes between multiple ISPs. The emergence of BGP has led to a major revolution in the Internet. It connects multiple ISPs and truly becomes a global network. The side effect is the Internet route explosion. Currently, there are about 60000 routes on the Internet, which is still the number after "aggregation. Configuring BGP requires a good understanding of user requirements, network conditions, and BGP protocols. You also need to be very careful. BGP runs at a core position. Once an error occurs, the loss may be very high! IPv6 technology

In the rapid development, the Internet will no longer just connect to computer networks, and it will develop into an information communication infrastructure similar to that of telephone networks and cable television networks. As a result, the IP (Internet Protocol) being used is no longer competent, and we are eager to see the emergence of the next generation of IP, namely IPv6.

IPv6 is a version of IP. In the Internet communication protocol TCP/IP, It is the transport protocol of the OSI model layer 3rd (Network Layer. Compared with the widely used IPv4 address proposed in 1974, the address is expanded from 32-bit to 128-bit. Theoretically, the number of addresses has increased from 4.3X109 to 4.3X1038. There are two main reasons why IPv6 must be switched from the current IPv4 address.

1. Due to the rapid development of the Internet, the number of addresses is insufficient, which makes the energy and cost of Network Management unbearable. Address depletion is the primary reason for the transition to a space with 128-bit addresses.

2. As the number of hosts increases, the route table for data transmission routes is constantly increasing. The processing performance of the router cannot keep up with this rapid growth. In the long run, it is difficult for Internet connections to provide stable services. Through IPv6, the number of routes can be reduced by an order of magnitude.

IPv6 is required to simplify Internet connection and make it easy to use. IPv6 can achieve this because it uses four technologies: address space expansion, address construction that can reduce the number of Route tables, automatic address setting, and improved security and confidentiality.

IPv6 inherits the advantages of IPv4 in routing technology and represents the future direction of routing technology. Many router manufacturers have invested a lot in the production of IPv6. Of course, IPv6 is also worth noting and inefficient. IPv4/NAT and IPv6 will coexist for a long time.

Vro configuration and debugging

Routers play an important role in computer networks and serve as a bridge between computer networks. It not only connects to different networks, but also selects data transmission paths and blocks illegal access.

Router configuration is not very easy for beginners. We will introduce general configurations and simple debugging of routers for your reference When configuring routers. This article uses Cisco2501 as an example.

Cisco2501 has an Ethernet port (AUI), a Console port (RJ45), an AUX port (RJ45), and two synchronous serial ports. It supports DTE and DCE devices, supports EIA/TIA-232, EIA/TIA-449, V.35, X.25, and EIA-530 interfaces.

1. Configuration

1. Configure the Ethernet port

# Conf t (configure the vro from the terminal)

# Int e0 (specified E0 port)

# Ip addr abcd xxxx (ABCD is an ethernet address and XXXX is a subnet mask)

# Ip addr abcd xxxx secondary (E0 port supports two address types at the same time. If the first one is A Class address, the second one is B or C Class address)

# No shutdown (activate E0 port)

# Exit

After completing the preceding configuration, run the ping command to check whether the E0 port is normal. If the port is not activated, it is often overlooked by beginners. Use the no shutdown command to activate the E0 port.

2. X.25 Configuration

# Conf t

# Int S0 (S0 port specified)

# Ip addr abcd xxxx (ABCD is the ip address of Ethernet S0, and XXXX is the subnet mask)

# Encap X25-ABC (encapsulate X.25 protocol. ABC specifies that X.25 is a DTE or DCE operation. The default value is DTE)

# X25 addr ABCD (ABCD is the X.25 port address of S0, provided by the Post Office)

# X25 map ip abcd xxxx br (mapped X.25 address. ABCD is the IP address of the Peer router (for example, S0) and XXXX is the X.25 port address of the Peer router (for example, S0)

# X25 htc X (configure the maximum number of two-way channels. The value range of X is 1-4095. It must be configured according to the number actually provided by the Post Office)

# X25 nvc X (the number of virtual circuits configured, X cannot exceed the number actually provided by the post office; otherwise, normal data transmission will be affected)

# Exit

After the S0 port is configured, use the no shutdown command to activate the E0 port. If the ping to port S0 is normal, the ping to the mapped X.25 IP address, that is, the IP address of the Peer router port, may be caused by the following situations: 1) Local X.25 address configuration error, check with the Post Office again (the length of X.25 address is 13 characters); 2) the local ing IP address or X.25 address is incorrectly configured, And the configuration is correct; 3) the peer IP address or X.25 address is incorrectly configured; 4) the local or peer route configuration is incorrect.

Can communicate with the other party, but packet loss occurs. In this case, there are generally the following possibilities: 1) Poor line conditions, or poor contact between the NIC and RJ45 plug; 2) the value range of x25 htc's maximum two-way channel number X and the number of x25nvc virtual circuits X exceed the number actually provided by the post office. The larger the maximum number of two-way channels and the number of virtual circuits, the better, but it must not exceed the number actually provided by the post office. Otherwise, packet loss may occur.

3. leased line configuration

# Conf t

# Int S2 (specifying S2 port)

# Ip addr abcd xxxx (ABCD is an ip address of S2 and XXXX is a subnet mask)

# Exit

After the leased line port is configured, use the no shutdown command to activate the S2 port.

4. Frame Relay Configuration

# Conf t

# Int s0

# Ip addr abcd xxxx (ABCD is an ip address of S0, and XXXX is a subnet mask)

# Encap frante_relay (encapsulate the frante_relay Protocol)

# No nrzi_encoding (NRZI = NO)

# Frame_relay lmi_type q933a (LMIS uses the Q933A standard. There are three types of LMIS (Local management Interface): ANSI: T1.617, CCITTY: Q933A and Cisco-specific standards)

# Fram-relay intf-typ ABC (ABC is the frame relay device type, which are supported by DTE devices, DCE switches, or NNI (Network Contact Interfaces)

# Frame_relay interface_dlci 110 br (configure DLCI (data link connection identifier ))

# Frame-relay map ip abcd xxxx broadcast (establishes a frame relay ing. ABCD is the IP address of the other party, XXXX is the local DLCI number, and broadcast allows the broadcast to forward or update the route)

# No shutdown (activate this port)

# Exit

After configuring the S0 port for Frame Relay, run the ping command to check the S0 port. If the port is not activated, use the no shutdown command to activate the S0 port. If the ping to port S0 is normal and the IP address mapped by ping is abnormal, it may be a frame relay switch or the other party's configuration error. Comprehensive troubleshooting is required.

5. Configure synchronous/asynchronous ports (applicable to 2522)

# Conf t

# Int s2

# Ph asyn (configure S2 as an asynchronous port)

# Ph sync (configure S2 as the synchronization port)

6. Dynamic Route Configuration

# Conf t

# Router VPN 20 (using the OSPF routing protocol. Common routing protocols include RIP, IGRP, and IS-IS)

# Passive-interface serial0 (if S0 is connected to X.25, enter this command)

# Passive-interface serial1 (if S1 is connected to X.25, enter this command)

# Network ABCD (ABCD is the local ethernet address)

# Network XXXX (IP address with XXXX being S0)

# No auto-summary

# Exit

7. Static route Configuration

# Ip router abcd xxxx yyyy 90 (ABCD is the ethernet address of the Peer router, XXXX is the subnet mask, and YYYY is the WAN port address of the Peer router)

# Dialer-list 1 protocol ip permail

Ii. Integrated debugging

After all the vrouters are configured, you can perform a comprehensive debugging.

1. Activate the Ethernet port of the router and all the serial ports to be used. The method is to enter this port and execute no shutdown.

2. Add the default route (the ethernet address of the central router) to the host connected to the router ). Run the following command under a Unix Super User: router add default XXXX 1 (XXXX is the E0 port address of the router ). Add a default route to each host. Otherwise, communication will fail.

3. ping the Ethernet port of the local router. If the port fails, the Ethernet port may not be activated or is not in the same network segment. Ping the wide area network port. If the port fails, no default route is added. Ping the WAN port of the other Party. If no connection is available, the router configuration is incorrect. Ping the Ethernet port of the host. If the port fails, no default route is added to the host.

4. Add a gateway (static route) to the host X.25 of the leased line card ). The method is to execute: router add X. x. x. X Y.Y. y.Y 1 (X. x. x. X is the peer ethernet address, Y.Y. y.Y is the WAN address of the other party ).

5. Use Tracert to track the route to determine the CIDR block.

Q: What is a gateway?

-- A: A Gateway is an important part of a network connection device. It not only provides routing functions, but also converts between two different protocol sets, thus, different networks are interconnected. For example, a Net-ware LAN can access the ibm sna network through a gateway, so that the PC Using IPX can communicate with the IBM host on the SNA network.

Q: What is a vswitch?

-- A: a switch is also called a switch-type hub. It re-generates the information and forwards it to the specified port after internal processing. It can automatically address and exchange the information, because the switch sends each information package to the destination port independently from the source port according to the destination address of the information package, it avoids collision with other ports, the switch can transmit these packets without affecting each other at the same time, and prevent transmission collisions, improving the actual network throughput.

Q: What is Cascade?

-- Answer: cascade connects devices to be cascaded through cascade ports through twisted pair wires to increase the number of ports on the same network.

Q: What is a hub?

-- Answer: A hub is the smallest unit for centralized network management. It is only a device for signal amplification and transfer, and does not have automatic addressing and switching capabilities, as all data transmitted to the hub is broadcasted to each port connected to it, it is easy to cause data congestion.

Q: What is a server?

-- A: a server is a node with a fixed address that provides services to network users. It is an important part of resource sharing, servers include network servers, printing servers, terminal servers, disk servers, and file servers.

Q: What is a workstation?

-- A: workstation is a high-end microcomputer, usually equipped with a high-resolution Large Screen Display and a large volume of internal and external memory, it also has strong information processing and high-performance graphics, image processing and networking functions.

Q: What is a MAC address?

-- A: the MAC address is generally a 12-bit hexadecimal address used to identify the NIC. Generally, the MAC address of each Nic is unique.

What is an independent redundant disk array (RAID) technology an independent redundant disk array (RAID) is a public system used for high-capacity data storage at the server level. The RAID system uses many small-capacity disk drives to store a large amount of data and enhances reliability and redundancy. For computers, such an array is like a logical unit consisting of multiple disk drives.

RAID storage methods are diverse. Some types of RAID emphasize performance, while others emphasize reliability, fault tolerance, or error correction. Therefore, you can select a type based on the task to be completed. However, the common feature of all RAID systems-and its true advantage is the "Hot Swap" capability: users can take out a defective drive and insert a new one for replacement. For most types of RAID, data on a faulty disk can be automatically rebuilt without interrupting the server or system.

RAID is not the only way to protect large volumes of data. However, conventional backup and image software are slow, and if a drive fails, the system is often interrupted. Even if the disk does not cause server interruption, IT staff still need to disconnect the server to replace the drive. Instead, RAID uses images or parity information to reconstruct Data from the remaining drive without interrupting the system.

Level0, 3, and 5 are the three most common RAID implementation methods:

RAIDLevel0 is the most basic method for data segmentation. On a general hard drive, data is stored in the continuous sector of the same disk. RAID0 uses at least two disk drives and splits the data into several blocks ranging from 512 bytes to several megabytes. These data blocks are repeatedly written to the disk. Segment 1st is written to disk 1, segment 2nd is written to Disk 2, and so on. When the system reaches the last disk in the array, it is written to the next segment of Disk 1. Split data to evenly distribute I/O loads to all drives. Because the drive can be written or read at the same time, the performance is significantly improved. However, it does not have data protection capabilities. If a disk fails, data will be lost. RAID 0 is not applicable to critical task environments, but is suitable for video production and editing or image editing.

RAIDLevel3 includes data splitting. In addition, it also specifies a drive to store parity information. This provides a fault tolerance function, which is especially beneficial to access long continuous records in a data-intensive environment or a single user environment. RAID 3 needs to synchronize the spindle drive to prevent performance degradation for shorter records.

RAIDLevel5 is similar to Level0, but instead of dividing data into blocks, it splits the bit of each byte into multiple disks. This will increase the management cost. However, if a disk fails, it can be changed and the data can be rebuilt from the parity and Error Correction Codes. RAID 5 includes all read/write operations. It requires three to five disks to form an array, which is most suitable for multi-user systems that do not require key features or require almost no write operations.

Other uncommon RAID types:

RAIDLevel1 is a disk image. Everything written to disk 1 is also written to Disk 2 and can be read from any disk. In this way, instant backup is provided, but the maximum number of disk drives is required, which cannot improve performance. RAID 1 Provides optimal performance and fault tolerance in multi-user systems and is the easiest configuration to implement, which is best suited to financial processing, payroll, financial and high-availability Data Environments.

RAIDLevel2 is developed for the mainframe and supercomputer. It can correct data without interrupting work, but RAID2 tends to have a high data checksum and error correction rate.

RAIDLevel4 contains large data entries so that records can be read from any drive. This type is not supported for multiple simultaneous write operations, so it is rarely used.

RAIDLevel6 is rarely commercially available. It uses a second parity scheme allocated on different drives, extending RAID5. It can withstand failures of multiple drives at the same time, but performance-especially write operations-is poor, and the system needs an extremely complex controller.

RAIDLevel7 has a real-time embedded operating system used as the controller and a high-speed bus used for caching. It provides fast I/O but is expensive.

RAIDLevel10 consists of an array of data entries, each of which is a RAID 1 array of the drive. Similar to the fault tolerance capability of RAID1, it is designed for database servers that require high performance and redundancy, but do not require high capacity.

RAIDLevel53 is the latest type, and its implementation is the same as the Level0 data bar array. Each segment is a RAID3 array. Its redundancy and fault tolerance capabilities are the same as RAID3. This is beneficial to IT systems that require RAID 3 configurations with high data transmission rates, but it is expensive and inefficient.

WINS service

WINS is short for Windows Internet Name Server (Windows Internet Name Service. WINS provides name registration, update, release, and Conversion Services for NetBIOS names. These services allow the WINS server to maintain a dynamic database that links NetBIOS names to IP addresses, greatly reducing the network traffic burden.

I. Why do we need the WINS service?

By default, the NetBIOS name of each computer on the network is updated through broadcast. That is to say, if there are n computers on the network, so every computer needs to broadcast n-1 times. For small networks, this does not seem to affect network traffic, but when large networks are concerned, the network burden is increased. Therefore, WINS is especially important for large and medium-sized enterprises.

Ii. How WINS works

As mentioned above, the WINS server provides the client with the following basic services:

1. Name Registration

Name Registration is the process in which the client obtains information from the WINS server. In the WINS service, name registration is dynamic.

When a client starts, it sends a name registration information (including the Client IP address and computer name) to the configured WINS server. If the WINS server is running, if no other client computer has registered the same name, the server returns a message (including the name registration period-TTL) to the client computer ).

Like an IP address, each computer must have a unique computer name. Otherwise, communication will fail. If the name has been registered by another computer, the WINS service will verify that the name is in use. If the name is in use, registration fails (a message of Negative confirmation is returned); otherwise, registration can continue.

2. Name update

Because the client is assigned a TTL (storage period), all its registration has a certain period of time. After this period, the WINS server will delete the registration information of this name from the database. The process is as follows:

(1 ). after 1/8 of the current period, the client continuously tries to update its name registration. If no response is received, the WINS client repeats the update every two minutes until the current period has passed half.

(2) When the current period is over half, the WINS client will try to update its lease with the secondary WINS server. The process is the same as that of the preferred WINS server.

(3) If the client still fails after half of the time, the client returns to its preferred WINS server.

In this process, whether it is the preferred or secondary WINS server, once the name registration is successful, the name registration of the WINS client will be provided with a new TTL value.

WINS service Introduction (2)

3. Release the name

During the normal shutdown of the client, the WINS client sends a name release request to the WINS server to release the IP address and NetBIOS name mapped to the WINS Server database. After receiving the release request, the WINS server verifies whether the IP address and NetBIOS name exist in its database. If yes, the server can be released normally, otherwise, an error occurs (the WINS server sends a negative response to the WINS client ).

If the computer is not properly shut down, the WINS server will not know that its name has been released, and the name will not expire until the WINS name registration record expires.

4. name resolution

When the client needs the WINS server to resolve the name in many network operations, for example, when using shared files from other computers on the network, you need to specify two things to get shared files: the system name and the shared name must be converted to an IP address.

The name resolution process is as follows:

(1) When the client computer wants to convert a name, it first checks the local NetBIOS name cache.

(2 ). if the name is not in the local NetBIOS name cache, a name is sent to the preferred WINS Server (sent every 15 seconds, three times in total). If the request fails, the same request is sent to the selected WINS.

(3) If all of them fail, you can use other methods for name resolution (such as local broadcast, lmhosts file and hosts file, or DNS.

Iii. Requirements for WINS servers and clients

1. Microsoft's requirements for Servers

(1). At least one preferred WINS server and one secondary WINS server are provided to provide fault tolerance.

(2) a wins server can process nearly 1500 name registration and about 4500 name queries every minute. Therefore, we strongly recommend that you use a preferred server and a secondary WINS server to drive up to 10000 clients.

(3) If the WINS server and the client are not on the same subnet, the performance of the router must be taken into account.

2. Client Requirements

Almost all Microsoft clients supporting network interconnection can be WINS clients. The following lists clients that can work with WINS:

* Windows NT Server 3.5x, 4.0

* Windows NT Workstation 3.5x, 4.0

* Windows 9x/me/2000

* Windows for Workgroups with TCP/IP-32

* Microsoft Network Client 3.0 for MS-DOS

* LAN Manager 2.2c for MS-DOS

DOS-based clients can also use the WINS server for name resolution, but you must add static entries to the WINS server.

Q: What is "DNS "? Why is it Chinese?

A: DNS, simply put, is the Domain Name System. If it is translated into Chinese, it is the "Domain Name System ".

Q: What is the purpose of DNS?

A: In a TCP/IP network (such as the Internet) Environment, DNS is a very important and common system. The main function is to convert Domain names that are easy to remember and IP addresses that are hard to remember. The network host that runs the DNS service above can be called the DNS Server. Basically, we usually think that DNS only converts Domain Name to IP Address, and then uses the IP Address to connect (commonly known as "forward resolution "). In fact, the function of converting an IP Address to a Domain Name is also quite common. When login is sent to a Unix workstation, the workstation will perform reverse lookup, find out where you are connecting (commonly known as "reverse resolution ").

Q: How does DNS work?

A: DNS operates in layers. For example, the Domain Name of the Harbin Institute of Technology is bbs.hit.edu.cn. This Domain Name is not from the air, but is allocated from .edu.cn .. Edu.cn is also granted from. cn (delegation .. Where does cn come from? The answer is from ".", that is, the so-called "root domain. The root Domain is already the top layer of Domain Name. The "." layer is managed by InterNIC (Internet Network InFORMation Center. Domain names all over the world are granted at one layer.

Q: When I check a Domain Name, how does DNS find its IP address?

A: for example, if the Domain Name we checked today (as a dns query) is bbs.hit.edu.cn, the DNS Server will handle this:

(1) Your Computer (either a PC or a workstation) sends a question to the DNS Server set for this computer. Question: What is the IP address of bbs.hit.edu.cn?

(2) This DNS will first check whether it is in its cache. If so, the answer will be lost. If not, check the top header. On the DNS Server, you must set "." To ask who to ask. So at this time, it will go to any DNS on the "." layer (currently "." has 13 servers) and ask: Who should I ask?

(3) The DNS at the "." layer will answer to who the. cn Domain is going to query (and the DNS you are using will cache the answer ).

(4) Next, the DNS you use will ask the DNS at the. cn layer: .edu.cn who will ask?

(5) On this layer of. cn, the answer will be .edu.cn to whom you want to query (and the DNS you use also caches the answer ).

(6) until bbs.hit.edu.cn replied: the IP address of bbs.hit.edu.cn is 202.118.224.2 (cache again ).

After so many processes, I finally got this IP address, and then I can make further connections. It should be noted that a question is asked at each layer, and the answer is recorded (cache starts), and it will be forgotten (it depends on how long it takes to cache the layer ).

Q: How do I configure DNS?

A: If you only want to use DNS, you only need to set it in the Network Properties of TCP/IP. The setting method is related to the operating system used. For example, for Windows 9x, find the DNS part in "Control Panel"> "network"> "TCP/IP"> "properties" and set it. Unix is set in the/etc/resolv. conf file (if you want to set up a DNS Server, it is not discussed here ).

Q: Which DNS is the latest?

A: If you know that DNS runs in a hierarchical architecture, you should know that the DNS closest to you is the best.

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