Virtual Private Networks is a concept introduced to implement global Wide Area Network(WAN) on the Internet. This way enormous costs involved in the traditional implementation of these networks i.e. through dedicated lines or satellite links is reduced considerably. A way to maintain fast, secure and reliable communications is attained wherever the offices are.
In the VPN, Internet is used as the data pipelined replacing the traditional datalines. This approach is just right for small and medium sized business firms. Now, many companies are creating their own VPN (virtual private network) to accommodate the needs of remote employees and distant offices. Each remote member of your network can communicate in a secure and reliable manner using the Internet as the medium to connect to the private LAN, by simply making a contract with the ISP. A VPN can grow to accommodate more users and different locations much easier than a leased line. In fact, scalability is a major advantage that VPNs have over typical leased lines. Unlike with leased lines, where the cost increases in proportion to the distances involved, the geographic locations of each office matter little in the creation of a VPN.
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.
A simple VPN model is shown below.
VIRTUAL PRIVATE NETWORKS
A company has its Main office, Remote office, Home office at various sites and these can interact with each other via the virtual network.
2. VPN TYPES
We all know WAN is simply the collection of local area networks,each located in geographically diverse locations connected to each other to form a single network. Leased lines which were initially used though forms a private network,it ought to be expensive. But VPN,using the power of the public medium,it helped to create a private connection called tunnel to switch data from one geographical location to the other.
A VPN provides network to network or remote user to network connectivity via the encrypted tunnel.Datas must be encapsulated in a IP packet before it can be sent across a VPN.Network users use various encryption and authentication schemes to provide security.Some VPN require specialisedv hardware,while some may require specialised software or some both that adds VPN capabilities to firewall,server or router.
Since VPN depends critically on the Internet,ISP becomes drivers of VPN technology. Therefore organisation using VPN becomes dependent on the ISP.If ISP faces bandwidth limitation or technical difficulties, the VPN will also face the same.
VPN can be of following types:
SITE TO SITE
Also called a virtual private dial-up network (VPDN), this 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.
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 either:
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.
The following is the examples of the three types of VPN.
Virtual Private Network protect tunelled dat through a combination of encryption, mutual host authentcation and protocol tunelling. One of the most basic method of protecting transmitted data is encryption.This involves scrambling the transmitted data using mathematical formula,so that even though the data transmission may be intercepted, it cannot be recovered without the correct key.
Encryption can be either be hardware enabled through network devices like routers or through software.While in the case of software,encryption takes place when you correct through the tunneling protocol like PTTP,in the case of router encryption it is performed on the fly.
One of the biggest difficulty encountered over the Internet is identifying the person or a computer at the other end of the wire.This is addressed by the authentication,a process where the two hosts verify eachother.This can be done through the X.2509 standard digital certificate which exchages electronic signatures between the two parties.This electronic signature is then verified by a trust third party,usually a public-certifying authority or the company`s own certificate server.
Alternatively,the host can also verify each other using protocols like Secure Shell(SSH).In this case the hosts exchange two keys, a host key and a server key. The receiving computer compares the host key with the keys inthe database. If the keys chacks out, the computer at the other end is validated as a genuine case.The PC then generates a session key using the host an the server key which is used to encrypt data transmission between the two computers.To ensure a high level of protection,the server key is changed on an hourly basis.
Finally there is a protocol tunneling. When data is transmitted on a network in the form of packets, the header-which gives information on the packet source, destination and number of packets transmitted- is in text format. The information can be used by hackers to gain access to either the system or the data being transmitted. Protocol tunneling takes data packets, encrypts them and then encapsulates them again in another clear text packet. This ensures that even if data transmission is intercepted the original header information is not available.Once these packets reach their destination,a router equipped with encryption and decryption capabilities decrypts the packet restoring the original data packets.
The too old trend or large companies to have own Ëœfully privateâ„¢ dial â€œin networks(completely with modem banks, access servers and technical service personnel deployed at each company sites is being reversed as the ubiquitious presence of Internet access site makes it attractive to use the resources offered by the Internet service providers(ISP).Such outsourcing allows employees to dial-in to an access server at a nearby ISP site and send packets over the Internet router for delivery to their Co. home networks. The very router vendor who provide VPN tunnels between permanent Co. sites are also competing for the oppurtuinity to provide VPN tunnels for dial-in users as well.But they are handicapped in the solution they can offer because they model tunnels as router-to-router constructs though there`s no router at the user end.If these vendors are to have a share in the outsourcing of a company`s dial-in service,this has to be achieved using one of the following models:
Outsource a private site
Share an outsourced site
Outsource a private access server
Share an access server
OUTSOURCE A PRIVATE SITE
A company desiring to outsource its access responsibility can ask an ISP to manage a site for it.ISPs themselves generally put their own dial-up equipment in the locations are termed as points of presence(POP).Under this model,a company may enter into a contract with the ISP to establish private POPs for its employees.This really moves the company`s private dial-up equipment to the site which is managed by the ISP.
If the resources of a POP are dedicated to a single company, then the POP is not different from a remote company site, and therefore the same routing equipment used at the company`s headquarters can be used at the POP. Since the site is private, all packets at the site can be in the clear. Tunnels only run between the router at the POP and the router at the company`s headquarters.
This approach offloads the access responsibility to the ISP, but it is likely to be more expensive than any other option because equipment cost are not shared. It has the further disadvantage that it require private facilities at as many POP as needed to provide local access to employees. Such an arrangement also locks employees.
Finally, an ISP has to manage a list of authorized user name and password on behalf of the company to help control access to the private site.All this necessitates that a very close relationship exists between the outsourcing company and the ISP for this model to succeed.In this model,if the company employees want to simultaneously access company and Internet resources,they tunnel to the company ,and then venture out to the Internet as though they were initiating contact from their place of work.
SHARE AN OUTSOURCED SITE
This model is an extension of the previous one in that a number of companies enter into a contract with an ISP to avail of the latterâ„¢s access service not privately, but in a shared manner. The major benefit, of course. is the resulting cost saving for the outsourcing company. In this model, we presume that each company using the shared site provides a router to tunnel its private traffic back to its headquarters.
If the equipment at the POP is not dedicated to a single company, the shared access server and LAN element need to be trusted, since company packets will be vulnerable on their way to and from the companyâ„¢s dedicated router. Such packets are exposed to ISP personnel at the site, and are subject to routing misadventures that expose them more generally to the entire Internet, and in particular to other companies who have their own encrypting routers on the POPâ„¢s shared LAN. If access servers are shared then user and password databases will be co-mingled at the site, and the access server software will have to be careful enough to direct all packets from a given dial-in port to the one and only one tunneling router. If packets go through the wrong tunnel, They will end up at the wrong headquarters.
In this model, users cannot go through their tunnel to work, and then on to the Internet without running the risk that their return packets will be routed back through a wrong tunnel. This means that an Internet access all tunneling routers at the site are exposed to an arbitrary Internet packet traffic. This makes security considerations a major issue for outsourcing companies, and hence this model is not workable in many scenarios.
OUTSOURCE A PRIVATE ACCESS SERVER
The previous models are not very attractive in that they are expensive, restrictive, and in some cases not very secure. They treat the ISP as a trusted extension of the outsourcing company. Though site outsourcing may make sense in certain situations, it is not likely to become a common practice. Site outsourcing may not be favoured by router vendors, except when they can sell a bunch of new routers to ISPs. All this brings us to another approach.
Instead of beginning the tunnel at the site router on behalf of all access servers with the ISP, it should be possible to begin a tunnel at each access server. This way, packets received at a dial-in port can be encrypted and encapsulated, and thus enter the tunnel before leaving the server so that they are never in the clear on the ISP LAN. Placing the tunnel function in the access server is such a compelling improvement over the earlier two models that it has received a focal attention of all vendors. It has also provided the impetus for many new or proposed standards that may offer a multivendor interoperability for server-router tunnels.
This model assumes that an outsourcing company asks an ISP to deploy some access servers at each POP, and dedicate them for the companyâ„¢s employees. The phone numbers of these dedicated resources are made available only to company personnel. Of course, the ISP must know employee names and passwords so as to guard access to these servers, but if the servers are effectively protected, the company does not have to worry about uses on other servers getting into one of their tunnels. Under this scheme, new codes are required for both access servers and the HQ (headquarters) router.
This is because, among other things, there is more than one tunnel from all ISP sites. The router itself becomes just another dial-in server, having logical ports in place of physical ports. Each tunnel terminates at one of the routerâ„¢s logical ports, and from there the de-encapsulated, decrypted packets are gated on to the company LAN. To distinguish such a logical access server from routers, an increasingly popular term Ëœhome gatewayâ„¢ is being used. Almost all of these server-to-home gatewayâ„¢ tunneling schemes are direct outgrowths of ubiquitous PPP (point-to point protocol) schemes used for exchanging packets between desktops and access servers over telephone lines.
In tunneling schemes, the access server and the home gateway assume the roles played in PPP by the dialing desktop and the dialed access server respectively. Tunnel protocols allow for the user name and password originally collected by the ISP to be forwarded to the home gateway so that the company can perform user authentication if it wants to. However, the access server must not only perform the new tunnel functions, but also IPX and Appletalk encapsulation functions (these Ëœfunnyâ„¢ packets must be handled on the PPP link with the user. but are encapsulated in IP packets so that they never hit the ISP LAK). Also the company itself must worry about providing full service desktop software to all its employees as before. It is possible for employees to have two different accounts with the ISP so that they can alternately receive tunnel, or clear Internet service. Current approaches do not offer a way to support both tunnelled and clear traffic services simultaneously.
SHARE AN OUTSOURCED ACCESS SERVER
Because the new access servers are able to establish tunnels on behalf of each dial-in port, there is no reason why each tunnel cannot go to a different home gateway. Home gateways can be selected on the basis of user identity as authenticated by the ISP, and so tunnels from a single access server can go to different companies at the same time. Economy apart, this functionality is not necessarily any better than the prior scheme, and may be inferior in many ways. For example. in this model, company authentication data does need to be held by the ISP, and access servers need to be trusted more than ever before. In addition until tunneling protocols are truly interoperable, it may not be possible for access serves from vendor A to talk to home gateways from vendor B. This implies many constraints for ISPs in the deployment of servers and allocation of phone numbers, modem types, etc.
4. VPN PROTOCOLS
The term VPN has taken on many different meanings in recent years. VPNC has a white paper about VPN technologies (PDF format) that describes many of the terms used in the VPN market today. In specific, it differentiates between secure VPNs and trusted VPNs, which are two very different technologies.
For secure VPNs, the technologies that VPNC supports are
IPsec with encryption
L2TP inside of IPsec
For trusted VPNs, the technologies that VPNC supports are:
MPLS with constrained distribution of routing information.
IPsec is by far the most dominant protocol for secure VPNs. L2TP running under IPsec has a much smaller but significant deployment. For trusted VPNs, the market is split on the two MPLS-based protocols.
The various VPN protocols are defined by a large number of standards and recommendations that are codified by the Internet Engineering Task Force (IETF). There are many flavors of IETF standards, recommendations, statements of common practice, and so on. Some of the protocols used in IPsec are full IETF standards; however, the others are often useful and stable enough to be treated as standard by people writing IPsec software. Neither of the trusted VPN technologes are IETF standards yet, although there is a great deal of work being done on them to get them to become standards.
The IETF codifies the decisions it comes to in documents called "Requests For Comments". These are almost universally called by their acronym "RFCs". Many RFCs are the standards on which the Internet is formed.
The level of standardization that an RFC reaches is determined not only by how good the RFC is, but by how widely it is implemented and tested. Some RFCs are not solid standards, but they nonetheless document technologies that are of great value to the Internet and thus should be used as guidelines for implementing VPNs. For the purpose of defining VPNs, any protocol that has become an IETF Request For Comments (RFC) document can be treated as some what of a standard. Certainly, any IPsec-related RFC that has been deemed to be on the IETF "standards track" should certainly be considered a standard.
Before a document becomes an RFC, it starts out as an Internet Draft (often called "IDs" or "I-Ds"). IDs are rough drafts, and are sometimes created for no other benefit than to tell the Internet world what the author is thinking. On the other hand, there is often very good information in some IDs, particularly those that cover revisions to current standards.
Some Internet Drafts go along for years, but are then dropped or abandoned; others get on a fast track to becoming RFCs, although this is rare. Internet Drafts are given names when they first appear; if they become RFCs, the I-D name disappears and an RFC number is assigned.
It should be emphasized here that it is unwise to make any programming decisions based on information in Internet Drafts. Most IDs go through many rounds of revisions, and some rounds make wholesale changes in the protocols described in a draft. Further, many IDs are simply abandoned after discussion reveals major flaws in the reasoning that lead to the draft.
That being said, it is worthwhile to know which IDs pertain to areas of interest. The following is a list of the IDs that are related to Internet mail. Some of these drafts will likely become RFCs in the months or years to come, possibly with heavy revision; some will be merged with other drafts; others will be abandoned.
5. VPN SECURITY
A VPN uses several methods for keeping your connection and data secure:
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.
If you have been using the Internet for any length of time, and especially if you work at a larger company and browse the Web while you are at work, you have probably use firewall. For example, you often hear people in companies say things like, I can't use that site because they won't let it through the firewall.If you have a fast Internet connection into your home (either a DSL connection or a cable modem), you may have found yourself hearing about firewalls for your home network as well. It turns out that a small home network has many of the same security issues that a large corporate network does. You can use a firewall to protect your home network and family from offensive Web sites and potential hackers.
Basically, a firewall is a barrier to keep destructive forces away from your property. In fact, that's why its called a firewall. Its job is similar to a physical firewall that keeps a fire from spreading from one area to the next.
This 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:
In symmetric-key encryption, each computer has a secret key (code) that it can use to encrypt a packet of information before it is sent over the network to another computer. Symmetric-key requires that you know which computers will be talking to each other so you can install the key on each one. Symmetric-key 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 key to decoding the message. For example: 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 key, then encrypts the symmetric key with the public key of the receiving computer. The receiving computer uses its private key to decode the symmetric key. It then uses the symmetric key to decode the document.
Public-key encryption uses a combination of a private key and a public key. The private key is known only to your computer, while the public key 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 key, provided by the originating computer, and its own private key. A very popular public-key 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.
IPSEC FAVOURING FOR A SECURE SYSTEM
Internet 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 key 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
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.
6. RELIABILITY AND PERFORMANCE
Because VPN uses the Internet, they can incure reliability and performance problems due to congestion,dropped packets and other factors.This could cause problems for real time applications,such as telephony and video conferencing.
Some large ISPs are trying to alleviate reliability concerns by keeping all customer VPN traffic on their own backbone.
The primary advantage of a VPN is that it cut cost. Compared to the traditional WAN,VPN are a cheap way to build global networks,It partially eliminates the modem banks, access server, phone lines and other types of hardware organisations must install to provide remote access to traditional private networks. To connect two far flung networks, all that is the dedicated link or backbone between these two networks. Since the Internet is a public network, cost are shared by all Internet users, resulting in low access cost.
Another advantage is that network expansion becomes a function of how quickly one can get a leased data connection to the nearest ISP. For the sharing of networked resources by business partners is facilitated since the question of incompatible system is already addressed in the Internet. Remote entry by authorised users with Internet access is possible.
A well-designed VPN can benefit a company by the following factors.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 and Security.
And farall practical purposes a VPN is a transperent as a traditional WAN.Whatever can be done on a WAN can be done n a VPN
If the level of security provided is insufficient, then it can be hazardeous. Since VPN is connected to the public network-Intrnet, it is prone to be hacked. Though all the network have some basic security-user authentication thru password verification that prevents such access, they are often insufficient.
Therefore two key security issues are protecting the network from breaking and also protecting the integrity of data being transmitted and validate the identity of the user over the Internet. This can be achieved by using a combination of encryption, host authentication and protocol tunneling.
As the cost of setting up the global network is prohibitively costly for small and medium sized business, Virtual private network offers cheap way to build WAN. The problems accomplished by VPN concerns security and performance. The standardisation of VPN technology will lead to its wide spread use among network users.
1. The book titled Security VPNs by Carton R Davis
2. The book titled computer Networks by Halsaal
3. The book titled computer Networks by Andrews Tanenbaum
2. VPN TYPES:
2.1. REMOTE ACCESS
2.2. SITE TO SITE
3.1. PRIVATE NETWORKS
3.2. OUTSOURCED SHARED MODELS
3.2.1. OUTSOURCE A PRIVATE SITE
3.2.2. OUTSOURCE A PRIVATE SITE
3.2.3. SHARE AN OUTSOURCED SITE
3.2.4. OUTSOURCE A PRIVATE ACCESS SERVER
3.2.5. SHARE AN ACCESS SERVER
4.1.2. INTERNET DRAFTS
5.3. IPSec PROTOCOL
5.4. AAA SERVER
6. RELIABILITY N PERFORMANCE
I would like to express my gratitude to our principal, Prof. K. Achuthan for providing the adequate facilities required for the completion of the seminars.
Next, I would like to thank the Head of the Computer Department
Mr. Agni Sarman Namboodiri, I would also like to thank my seminars conductor Mr. Zaheer and also Ms. Deepa for their excellence guidance in preparation and presentation of the topic.
And finally, to the most important person, the God Almighty, for without his blessings, all this wouldnâ„¢t have been possible.