Charpter six Applications of internet

Keywords:
VPN 虚拟专用网
public network 公用网
gateway 网关
router 路由器
firewall 防火墙
protocol 协议
link 链路 链接
encryption 加密
authentication 验证
tunneling 隧道技术
ISP 因特网服务提供商
POP 接入点
roaming user 漫游用户
intranet 英特网内部网
extranet 英特网外部网
web server 万维网服务器
laptop 膝上

6.1 Virtual Private Network(vpn)
1.why build a virtual private network
Unitil now there has always been a clear divsion between public and private networks, A public network, like the public telephone system and the internet, is a large collection of unrelated peers that exchange information more or less freely with each other, the people with access to the public network may not have anything in common, and any given person on that network may only communicate with a small fraction of his potential users.

A private network is composed of computers owened by a single organization that share information specifically with each other, They’re assured that thay are going to be the only be seen by other in the group, The typical corpate Local Area network or wide Area network is an example of a private network, The line between a private and public network has always been drawn at the gateway touter, where a company will erect a firewall to keep intruders from the public network out of their private network, or to keep their owen internal users from perusing to the public network.

There also was a time, not too long ago, when companies could allow their lans to operate as sparate, isolate islands. each branch office might have its own favorite network protocok none of which might be compatible with other office’setups, As more company resources moved to computers, however, there came a need for these offices to interconnect, this was traditionally done using lased phone lines of varying speeds, By using leased lines, a company can be assured that the connection is always available, and private, leased phone lines. however. can be expenses, if a company has offices across the country, the cost can be prohibitive, private networks also have trouble handling moving users, sunch as traveling salespeople, if the salesoerson dones’t happen to be near one of the corpate computers, he or she have a dial into a corporation’s modem long-distance, which is an extremly expensive proposition.
The virtual privte network is a concept that blurs the line between a public and private network. vpns allow you to create a secure, private network over a public network sunch as the internet, they can be created using software, hardware, or a combination of the two the creates a secure link between peers over a publix network. this is done through encryption, authentication,packet tunneling, and firewalls.

2.what does a vpn do?
A virtual private network is a way to simulate a private network over a public network, sunch as the internet, it is called “virtual” because it depends on the use of virtual connections -that is, temporary connections that have no real physical presence, but consisit of packets rounted over various machines on the internet on an ad hoc basic. secure virtual connections are created between two machines ,a machine and a network. or two network.
Using the internet for remote access saves a lot of money, you’ll be able to dial in wherever your internet service provide has a point of presense. if you choose an isp with nationwide pops. there’s good chance your lan will be a local phone call away, some isps have expended internationally as well, or have alliance with isps overseas, even many of this writing, unlimited access dial up ppp accounts, suitable for business use, are around $25 per month per user, At any rate, well choen ISP accounts should be cheaper than setting up a modem pool for remote users and playing the long-distance bill for roaming users, Even toll free access from an ISP is typically cheaper than having your own toll-free number, because ISPs purchase hours in bulk from the long-distance companies.

3.How VPNs relate to internets
Virtual private networks can be used to expand the reach of an intranets, Since Intranets are typically used to communicate proprietary information, you don’t want them accessible from the internet, They may be cases. however, where you’ll want far- flung offices to share date to remote users to connect to your internet, and these users may be using the internet as their means of connection, A VPN will allow them to connect to the internet securely, so there are no fears of sensitive information leaving the network uprotected, you might see this connection also referred to as an “extranet”.
Using our previous example of the customer database, it’s easy to see how to a VPN could expand the internet application’s functionality, Suppose most of your salespeople are on the road, or work from home, There’s no reason why shouldn’t be able to use the internet to access the web server that houses the customer datebase application, you don’t want just anyone to be able to access the information, however, and you’re also worried about the information itself flowing unencrypted over the internet, A VPN can provide a secure link between the salespeople’laptop and the internet wen server runing the database, and encrypt the data going between them. VPNs give you flexibility, and allow practivally any corporate network service to be used to access the internet.