How Virtual Private Networks Work.
The world has changed a lot in the last couple of decades. Instead of simply dealing with local or regional concerns, many businesses now have to think about global markets and logistics. Many companies have facilities spread out across the country or around the world, and there is one thing that all of them need: A way to maintain fast, secure and reliable communications wherever their offices are.
Until fairly recently, this has meant the use of leased lines to maintain a wide area network (WAN). Leased lines, ranging from ISDN (integrated services digital network, 128 Kbps) to OC3 (Optical Carrier-3, 155 Mbps) fiber, provided a company with a way to expand its private network beyond its immediate geographic area. A WAN had obvious advantages over a public network like the Internet when it came to reliability, performance and security. But maintaining a WAN, particularly when using leased lines, can become quite expensive and often rises in cost as the distance between the offices increases.
As the popularity of the Internet grew, businesses turned to it as a means of extending their own networks. First came intranets, which are password-protected sites designed for use only by company employees. Now, many companies are creating their own VPN (virtual private network) to accommodate the needs of remote employees and distant offices.
Basically, a VPN is a private network that uses a public network (usually the Internet) to connect remote sites or users together. Instead of using a dedicated, real-world connection such as leased line, a VPN uses"virtual"connections routed through the Internet from the company's private network to the remote site or employee. In this article, you will gain a fundamental understanding of VPNs, and learn about basic VPN components, technologies, tunneling and security
What Makes a VPN ?
A well-designed VPN can greatly benefit a company. For example, it can:
Extend geographic connectivity
Improve security
Reduce operational costs versus traditional WAN
Reduce transit time and transportation costs for remote users
Improve productivity
Simplify network topology
Provide global networking opportunities
Provide telecommuter support
Provide broadband networking compatibility
Provide faster ROI (return on investment) than traditional WAN
What features are needed in a well-designed VPN? It should incorporate:
Security
Reliability
Scalability
Network management
Policy management
There are three types of VPN. In the next couple of sections, we'll describe them in detail.
Remote-Access VPN
There are two common types of VPN. Remote-access, also called a virtual private dial-up network (VPDN), is a user-to-LAN connection used by a company that has employees who need to connect to the private network from various remote locations. Typically, a corporation that wishes to set up a large remote-access VPN will outsource to an enterprise service provider (ESP). The ESP sets up a network access server (NAS) and provides the remote users with desktop client software for their computers. The telecommuters can then dial a toll-free number to reach the NAS and use their VPN client software to access the corporate network.
A good example of a company that needs a remote-access VPN would be a large firm with hundreds of sales people in the field. Remote-access VPNs permit secure, encrypted connections between a company's private network and remote users through a third-party service provider.
Site-to-Site VPN
Through the use of dedicated equipment and large-scale encryption, a company can connect multiple fixed sites over a public network such as the Internet. Site-to-site VPNs can be one of two types:
Intranet-based - If a company has one or more remote locations that they wish to join in a single private network, they can create an intranet VPN to connect LAN to LAN.
Extranet-based - When a company has a close relationship with another company (for example, a partner, supplier or customer), they can build an extranet VPN that connects LAN to LAN, and that allows all of the various companies to work in a shared environment.
VPN Security: Firewalls
A well-designed VPN uses several methods for keeping your connection and data secure:
Firewalls
Encryption
IPSec
AAA Server
In the following sections, we'll discuss each of these security methods. We'll start with the firewall.
A firewall provides a strong barrier between your private network and the Internet. You can set firewalls to restrict the number of open ports, what type of packets are passed through and which protocols are allowed through. Some VPN products, such as Cisco's 1700 routers, can be upgraded to include firewall capabilities by running the appropriate Cisco IOS on them. You should already have a good firewall in place before you implement a VPN, but a firewall can also be used to terminate the VPN sessions
VPN Security: Encryption
Encryption is the process of taking all the data that one computer is sending to another and encoding it into a form that only the other computer will be able to decode. Most computer encryption systems belong in one of two categories:
Symmetric-k*y encryption
Public-k*y encryption
In symmetric-k*y encryption, each computer has a secret k*y (code) that it can use to encrypt a packet of information before it is sent over the network to another computer. Symmetric-k*y requires that you know which computers will be talking to each other so you can install the k*y on each one. Symmetric-k*y encryption is essentially the same as a secret code that each of the two computers must know in order to decode the information. The code provides the k*y to decoding the message. Think of it like this: You create a coded message to send to a friend in which each letter is substituted with the letter that is two down from it in the alphabet. So"A"becomes"C,"and"B"becomes"D". You have already told a trusted friend that the code is"Shift by 2". Your friend gets the message and decodes it. Anyone else who sees the message will see only nonsense.
The sending computer encrypts the document with a symmetric k*y, then encrypts the symmetric k*y with the public k*y of the receiving computer. The receiving computer uses its private k*y to decode the symmetric k*y. It then uses the symmetric k*y to decode the document.
Public-k*y encryption uses a combination of a private k*y and a public k*y. The private k*y is known only to your computer, while the public k*y is given by your computer to any computer that wants to communicate securely with it. To decode an encrypted message, a computer must use the public k*y, provided by the originating computer, and its own private k*y. A very popular public-k*y encryption utility is called Pretty Good Privacy (PGP), which allows you to encrypt almost anything. You can find out more about PGP at the PGP site.
VPN Security: IPSec
nternet Protocol Security Protocol (IPSec) provides enhanced security features such as better encryption algorithms and more comprehensive authentication.
IPSec has two encryption modes: tunnel and transport. Tunnel encrypts the header and the payload of each packet while transport only encrypts the payload. Only systems that are IPSec compliant can take advantage of this protocol. Also, all devices must use a common k*y and the firewalls of each network must have very similar security policies set up. IPSec can encrypt data between various devices, such as:
Router to router
Firewall to router
PC to router
PC to server
VPN Security: AAA Servers
AAA (authentication, authorization and accounting) servers are used for more secure access in a remote-access VPN environment. When a request to establish a session comes in from a dial-up client, the request is proxied to the AAA server. AAA then checks the following:
Who you are (authentication)
What you are allowed to do (authorization)
What you actually do (accounting)
The accounting information is especially useful for tracking client use for security auditing, billing or reporting purposes.
VPN Technologies
Depending on the type of VPN (remote-access or site-to-site), you will need to put in place certain components to build your VPN. These might include:
Desktop software client for each remote user
Dedicated hardware such as a VPN concentrator or secure PIX firewall
Dedicated VPN server for dial-up services
NAS (network access server) used by service provider for remote-user VPN access
VPN network and policy-management center
Because there is no widely accepted standard for implementing a VPN, many companies have developed turn-k*y solutions on their own. In the next few sections, we'll discuss some of the solutions offered by Cisco, one of the most prevelant networking technology companies.
The world has changed a lot in the last couple of decades. Instead of simply dealing with local or regional concerns, many businesses now have to think about global markets and logistics. Many companies have facilities spread out across the country or around the world, and there is one thing that all of them need: A way to maintain fast, secure and reliable communications wherever their offices are.
Until fairly recently, this has meant the use of leased lines to maintain a wide area network (WAN). Leased lines, ranging from ISDN (integrated services digital network, 128 Kbps) to OC3 (Optical Carrier-3, 155 Mbps) fiber, provided a company with a way to expand its private network beyond its immediate geographic area. A WAN had obvious advantages over a public network like the Internet when it came to reliability, performance and security. But maintaining a WAN, particularly when using leased lines, can become quite expensive and often rises in cost as the distance between the offices increases.
As the popularity of the Internet grew, businesses turned to it as a means of extending their own networks. First came intranets, which are password-protected sites designed for use only by company employees. Now, many companies are creating their own VPN (virtual private network) to accommodate the needs of remote employees and distant offices.
Basically, a VPN is a private network that uses a public network (usually the Internet) to connect remote sites or users together. Instead of using a dedicated, real-world connection such as leased line, a VPN uses"virtual"connections routed through the Internet from the company's private network to the remote site or employee. In this article, you will gain a fundamental understanding of VPNs, and learn about basic VPN components, technologies, tunneling and security
What Makes a VPN ?
A well-designed VPN can greatly benefit a company. For example, it can:
Extend geographic connectivity
Improve security
Reduce operational costs versus traditional WAN
Reduce transit time and transportation costs for remote users
Improve productivity
Simplify network topology
Provide global networking opportunities
Provide telecommuter support
Provide broadband networking compatibility
Provide faster ROI (return on investment) than traditional WAN
What features are needed in a well-designed VPN? It should incorporate:
Security
Reliability
Scalability
Network management
Policy management
There are three types of VPN. In the next couple of sections, we'll describe them in detail.
Remote-Access VPN
There are two common types of VPN. Remote-access, also called a virtual private dial-up network (VPDN), is a user-to-LAN connection used by a company that has employees who need to connect to the private network from various remote locations. Typically, a corporation that wishes to set up a large remote-access VPN will outsource to an enterprise service provider (ESP). The ESP sets up a network access server (NAS) and provides the remote users with desktop client software for their computers. The telecommuters can then dial a toll-free number to reach the NAS and use their VPN client software to access the corporate network.
A good example of a company that needs a remote-access VPN would be a large firm with hundreds of sales people in the field. Remote-access VPNs permit secure, encrypted connections between a company's private network and remote users through a third-party service provider.
Site-to-Site VPN
Through the use of dedicated equipment and large-scale encryption, a company can connect multiple fixed sites over a public network such as the Internet. Site-to-site VPNs can be one of two types:
Intranet-based - If a company has one or more remote locations that they wish to join in a single private network, they can create an intranet VPN to connect LAN to LAN.
Extranet-based - When a company has a close relationship with another company (for example, a partner, supplier or customer), they can build an extranet VPN that connects LAN to LAN, and that allows all of the various companies to work in a shared environment.
VPN Security: Firewalls
A well-designed VPN uses several methods for keeping your connection and data secure:
Firewalls
Encryption
IPSec
AAA Server
In the following sections, we'll discuss each of these security methods. We'll start with the firewall.
A firewall provides a strong barrier between your private network and the Internet. You can set firewalls to restrict the number of open ports, what type of packets are passed through and which protocols are allowed through. Some VPN products, such as Cisco's 1700 routers, can be upgraded to include firewall capabilities by running the appropriate Cisco IOS on them. You should already have a good firewall in place before you implement a VPN, but a firewall can also be used to terminate the VPN sessions
VPN Security: Encryption
Encryption is the process of taking all the data that one computer is sending to another and encoding it into a form that only the other computer will be able to decode. Most computer encryption systems belong in one of two categories:
Symmetric-k*y encryption
Public-k*y encryption
In symmetric-k*y encryption, each computer has a secret k*y (code) that it can use to encrypt a packet of information before it is sent over the network to another computer. Symmetric-k*y requires that you know which computers will be talking to each other so you can install the k*y on each one. Symmetric-k*y encryption is essentially the same as a secret code that each of the two computers must know in order to decode the information. The code provides the k*y to decoding the message. Think of it like this: You create a coded message to send to a friend in which each letter is substituted with the letter that is two down from it in the alphabet. So"A"becomes"C,"and"B"becomes"D". You have already told a trusted friend that the code is"Shift by 2". Your friend gets the message and decodes it. Anyone else who sees the message will see only nonsense.
The sending computer encrypts the document with a symmetric k*y, then encrypts the symmetric k*y with the public k*y of the receiving computer. The receiving computer uses its private k*y to decode the symmetric k*y. It then uses the symmetric k*y to decode the document.
Public-k*y encryption uses a combination of a private k*y and a public k*y. The private k*y is known only to your computer, while the public k*y is given by your computer to any computer that wants to communicate securely with it. To decode an encrypted message, a computer must use the public k*y, provided by the originating computer, and its own private k*y. A very popular public-k*y encryption utility is called Pretty Good Privacy (PGP), which allows you to encrypt almost anything. You can find out more about PGP at the PGP site.
VPN Security: IPSec
nternet Protocol Security Protocol (IPSec) provides enhanced security features such as better encryption algorithms and more comprehensive authentication.
IPSec has two encryption modes: tunnel and transport. Tunnel encrypts the header and the payload of each packet while transport only encrypts the payload. Only systems that are IPSec compliant can take advantage of this protocol. Also, all devices must use a common k*y and the firewalls of each network must have very similar security policies set up. IPSec can encrypt data between various devices, such as:
Router to router
Firewall to router
PC to router
PC to server
VPN Security: AAA Servers
AAA (authentication, authorization and accounting) servers are used for more secure access in a remote-access VPN environment. When a request to establish a session comes in from a dial-up client, the request is proxied to the AAA server. AAA then checks the following:
Who you are (authentication)
What you are allowed to do (authorization)
What you actually do (accounting)
The accounting information is especially useful for tracking client use for security auditing, billing or reporting purposes.
VPN Technologies
Depending on the type of VPN (remote-access or site-to-site), you will need to put in place certain components to build your VPN. These might include:
Desktop software client for each remote user
Dedicated hardware such as a VPN concentrator or secure PIX firewall
Dedicated VPN server for dial-up services
NAS (network access server) used by service provider for remote-user VPN access
VPN network and policy-management center
Because there is no widely accepted standard for implementing a VPN, many companies have developed turn-k*y solutions on their own. In the next few sections, we'll discuss some of the solutions offered by Cisco, one of the most prevelant networking technology companies.
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