Computer Network Technology and Application

Chapter 18 Network Interconnection Technology (3)
【例5-4】　路由表是路由器R2的，一个数据包到达R2后，可以通过直接路由到达网络20.0.0.0和30.0.0.0；但要通过路由器R1和R3，才能把数据报转发给网络10.0.0.0和40.0.0.0，即要使用间接路由。

The routing table includes the destination network and the next forwarding router, "direct delivery" means direct routing, 20.0.0.1 is the IP address of the R1 router in the network 20.0.0.0, similarly, 30.0.0.2 is the R3 router in the network 30.0.0.0 IP address in . R2 can only recognize the IP addresses of other devices in the same network as itself.

5.5 Cases of Internet using routers
5.5.1 Using Access Router

The access router is very important for a local area network, and the router can be used as a front-end firewall to improve the security factor of the local network.

The following is an example of establishing a router connecting an enterprise to the Internet.

Because the router can have firewall, domain name filter, MAC address filter, prevent DoS (denial of service) attack, support user access management functions, fully guarantee the security of Internet cafes; moreover, routers with high performance and high stability can also be very Good guarantee of network speed.

Through this example, if you want to protect the local network, such as campus network, enterprise network, hospital network, community network, etc., you must choose a router with excellent performance before accessing the Internet. There are two purposes, one is to protect the local network, and the other is Then increase the network speed of Internet access.

On the router, there are at least two interfaces, one is connected to the outside, and the other is connected to the local network switch. The corresponding two ports are respectively configured with externally applied IP addresses (select fixed or dynamic IP according to the network service provider), and the other port is configured with the internal local network. IP address.Routing can also be configured according to the software of the router.

5.5.2 Enterprise Network Interconnection

This section uses the enterprise internal network as an example to introduce the interconnection between networks.

Suppose a company has its headquarters in Beijing and two other branches in Shanghai and Wuhan. The company needs to set up its own network so that employees in the three places can share information resources and access the Internet.In this example, only the backbone network is considered, not the computer connections.

The specific plan is as follows:

1. Headquarters network
The backbone adopts advanced network management switches, and the VLAN technology is used to limit the accessible range of each computer.

At the same time, it supports the port aggregation function, which can effectively improve the bandwidth of the backbone part and the reliability of the connection, which meets the needs of modern enterprises for reliability and speed.

Use a VPN router to directly access the WAN or use the ADSL service to access the Internet.

For the computer system within the department, different departments use series of intelligent switches or series of ordinary layer-100 switches as networking equipment to achieve [-]Mbps speed to the desktop according to the needs.

The server adopts gigabit network card, and the workstation adopts 10M/100M adaptive network card, which meets the requirements of fast Ethernet and is very practical.

For meeting rooms or exhibition halls, use wireless connection to maintain seamless connection with existing wired networks.

2. Branch network
Gigabit switches are used as the backbone; several Layer [-] switches are used to distribute in different departments; VPN routers are used to directly access the WAN.

For the computer system inside the headquarters, different departments use series of intelligent switches or series of ordinary layer-100 switches as networking equipment to achieve [-]Mbps speed to the desktop according to needs.

The server adopts gigabit network card, and the workstation adopts 10M/100M adaptive network card, which meets the requirements of fast Ethernet and is very practical.

For meeting rooms or exhibition halls, use wireless connection to maintain seamless connection with existing wired networks.

3. Interconnection between headquarters and branches
In this example, the intranet VPN technology is used to interconnect the networks in three regions.

Intranet VPN is a network connection method between the headquarters and branches of an enterprise through a VPN virtual network. This VPN is connected through the public Internet or a third-party private network. Enterprises with conditions can use optical fiber as a transmission medium.It is characterized by easy connection establishment and fast connection speed, and its biggest feature is that it provides the access authority of the entire network for each branch.

When the number of branches increases and the business development becomes more and more extensive, the network structure tends to be complicated and expensive.Using the VPN feature can set up a worldwide Intranet VPN on the Internet.Use Internet lines to ensure the interconnectivity of the network, and use VPN features such as tunnels and encryption to ensure the safe transmission of information on the entire Intranet VPN. IntranetVPN connects corporate headquarters, remote offices, and branch offices over a shared infrastructure using dedicated connections.Enterprises have the same policies as private networks, including security, quality of service (QoS), manageability, and reliability.

The focus of this case is to solve the problem of stable, high-speed, safe, and economical remote interconnection operation in the network environment, and secure management of access users to use the application system.

A server with Windows Server 2005 or above is installed in the intranet of the Beijing headquarters, and a routing and remote access server is established as the management center of the VPN network. The gateway of the headquarters application software database server points to the VPN server.

Equip a computer with Windows Server 2005 operating system in the intranet of Shanghai and Wuhan branches, and install "VPN dial-up". Notebooks and PDAs can also be interconnected with the corporate network in this way.The specific implementation is shown in Figure 5.6.

Or use the following options:
Both the Shanghai and Wuhan branches use routers with VPN dial-up function as access VPN gateway devices to establish connections between the branches and the headquarters.

This solution seems to be better than the previous one, but in actual networking, there is a problem with using a router to establish a VPN connection, that is, the dynamic nature of the address will make the VPN connection unstable, so this book recommends using the previous solution. functions of switches and routers.

【chapter summary】

The main contents of this chapter include network interconnection protocols, IPv4 IP address types and addressing methods, IP protocol, ARP protocol and ICMP protocol, routers and routing protocols RIP and OSPF.

【Difficulties in this chapter】

(1) Functions and applications of routers.

(2) No classification address.

(3) Routing protocol OSPF.

Exercise 5
[-]. Multiple choice questions

1. Which part of the IP address 205.140.36.86 represents the host number? ()
A.20 5
B.20 5.1 40
C.86
D.36.86
2. Which part of the IP address 129.66.51.89 represents the network number? ()
A.129.66
B.129
C.192.66.51
D.89
3. Suppose the IP address of a host is 192.168.5.121, and the subnet mask is 255.255.255.248, then the subnet number of the host is . ()

A.192.168.5.12
B.121
C.15
D.168
4. Under normal circumstances, which of the following statements is wrong? ()
A. The ARP table in the high-speed buffer is created manually.

B. The ARP table in the high-speed buffer is automatically established by the host.

C. The ARP table in the high-speed buffer is dynamic.

D. The ARP table in the high-speed buffer stores the mapping relationship between the host IP address and the physical address.

5. The router forwards the packet according to the grouping of the message ().

A. Port number

B. MAC address
C.IP address
D.Domain name
6. In the process of establishing routing, it is necessary to use algorithm selection () to make the transmission of packets more efficient.

A. Best route

B. Virtual Routing
C. Shortest route

D. Optimal memory allocation

7. There is a router Q between the two interconnected networks, and the IP of Q should have ().

A. The IP addresses assigned by the two networks respectively
B. Only one IP
C. Two different LLC addresses
D. A combination of two physical and one logical address

Two, short answer questions
1. Compare the difference between static and dynamic routing.

2. The characteristics and applicability of the short-answer RIP protocol.

3. What is direct routing?What is indirect routing?

4. In the routing table entry, what is the role of the default route?
5. What are the advantages of non-categorical addressing?
6. What is the applicable environment of OSPF protocol?
Experiment [-] to learn simple network settings
【Purpose】

(1) Learn how to configure the IP address.

(2) Learn simple routing settings.

【Experimental content】

(1) Configure a fixed IP address.

(2) Configure a dynamic IP address.

(3) Set the Windows2005Server computer as a software router.

[class hours] 2
【Experimental Requirements】

(1) Master the configuration method of IP address.

(2) Master the simple configuration method of routing.

【Experimental conditions】

At least two computers, one with Windows2003/2005Server operating system.

【Experimental steps】

1. Configure the fixed IP address of the computer
(1) On the WindowsXP/VISTA desktop, right-click "My Network Places" and click "Properties".

(2) In the My Network Places Properties dialog box, right-click the "Local Area Connection" icon and select the "Properties" option.

(3) Select the TCP/IP protocol.

(4) Click "Internet Protocol (TCP/IP)", click "Properties", select "Use the following IP address", fill in the IP address, subnet mask, default gateway, etc.

prompt:

The address in the figure is the internal network address, you need to choose a different IP address for each computer; the masks are all 255.255.255.0. For example, no settings are made; DNS is the server for resolving domain names; this example takes the internal network as an example, and if it is changed to other types of addresses, the method is similar.

(5) Click the "OK" button to complete the configuration.

2. Configure dynamic IP address
The method of configuring a dynamic IP address is as follows: in (1) of 4, select to obtain an address automatically, configure a dynamic IP address, and the other steps are the same.

3. View the IP parameters currently set by the computer
This experiment utilizes the "ipconfig" command.

(1) Enter the command prompt, click "Start" → "Programs" → "Accessories" → "Command Prompt"; (2) Enter ipconfig in the window and press the Enter key, you can see the current IP of each network connection Address, default gateway, DNS resolution and other items; (3) Enter ipconfig /all and press Enter to view detailed information.

4. Set up the router

The Microsoft Windows Server operating system has a "routing and remote access" service, which provides many economical functions and can work with a variety of hardware platforms and different types of network cards. The "Routing and Remote Access" service provides multi-protocol routing services, including LAN to LAN, LAN to WAN, virtual private network (VPN) and network address translation (NAT). The VPN service has been used in the experiments in Chapter 4. This chapter My experiment was to build a software router for two LANs.

The current experimental environment is two network segments, one is 192.168.1.0 and the other is 192.168.2.0.

Without a router, only hosts in the same IP subnet can communicate; if the hosts are not in the same network segment, they cannot communicate with each other even if they are connected through the same switch or hub.

The following methods can be used to realize the interconnection of two networks:

Bind two IP addresses on a Windows Server server, namely 192.168.1.1 and 192.168.2.1; start the routing service in this Server, and use Windows Server 2003 as a router to realize the interconnection of the two network segments.

(1) Click "Start" → "All Programs" → "Administrative Tools" → "Routing and Remote Access" to open the "Routing and Remote Access" management window.

(2) Select the "Routing and Remote Access" root directory, right-click the mouse, click to select "Add Server", select "This Computer", and click "OK".

(3) Configure and enable the router, select the server added in (2), right-click the mouse, and click to select the "Configure and enable routing and remote access" option.

(4) When the "Routing and Remote Access Setup Wizard" dialog box appears, click "Next", select "Secured connection between two private networks", and click "Next".

(5) In the "Demand-Dial Connection" dialog box, select the "No" radio button, and then click the "Next" button to continue.

(6) The wizard pops up a dialog box, click the "Finish" button, and the server installation is complete until now.

(7) Configure the IP address of the Server
Configure two IP addresses of the Windows Server server, 192.168.1.1 and 192.168.2.1 respectively.

① Configure the first IP address 192.168.1.1 for the Server according to the method of configuring the fixed IP address of the computer.

② Click Advanced in the dialog box, click the "Add" button under the "IP Address" item, enter the second IP address 2, and click "Add"→"OK".

(8) Configure static routing

① Click "Start" → "All Programs" → "Administrative Tools" → "Routing and Remote Access" to open the "Routing and Remote Access" management window.

② Select the sub-item "Static Route" under "IP Routing Selection", right-click the mouse, and click "New Static Route".

③Select the local connection interface, fill in the target network, and the corresponding target network mask, and fill in the IP address of the gateway. This experiment assumes that 192.168.1.1 is the gateway address; Click "OK" to complete the route configuration.

【Questions and Thoughts】

(1) What are the differences between the router function and the VPN in this experiment?
(2) If ADSL is used to connect to China Telecom's network, do I need to set a fixed IP address?

(End of this chapter)