VPN Access Strategies

VPN accessA virtual private network (VPN) is exactly what it sounds like: the network connection you create is virtual, because you can use it over an otherwise public network. Basically, you take two endpoints for the VPN tunnel, and all traffic between these two endpoints will be encrypted so that the data being transmitted is private and unreadable to the system in between. Different VPN solutions use different protocols and encryption algorithms to accomplish this level of privacy. VPNs tend to be protocol independent, at least to some degree, in that the VPN configuration is not on a per-port basis. Rather, once you have established the VPN tunnel, all applicable traffic will be routed across the tunnel, effectively extending the boundaries of your internal network to include the remote host. In this article, we will examine some of the issues involved in implementing VPN access.

VPN Access: Network Design

One of your first considerations when planning to provide for VPN access is the network design. Because the VPN tunnel needs two endpoints, one will be the remote workstation. The other will be a specially configured device for that purpose. This is generally called a VPN concentrator, because it acts as a common endpoint for multiple VPN tunnels. [As noted previously in this blog, Soekris makes affordable VPN cards that offload the CPU of the the computing intensive tasks of encryption and compression.] The remote system will effectively be using the concentrator as a gateway into the internal network; as such the placement of the concentrator is important: in a highly secured environment, the concentrator is placed in a DMZ sandwiched between two firewalls, one firewall facing the Internet, and the other facing internally. While this type of arrangement is the most secure, it takes more hardware to implement.


Another way to place the VPN concentrator inside a DMZ is to use an additional interface on the firewall as the DMZ in a “one-legged” configuration. This saves you having to implement an additional firewall, but still provides some isolation between the concentrator and the rest of the internal network. If an attacker compromised a remote host who was VPNed into the concentrator or compromised the concentrator itself, they would still have a firewall between them and the internal network. The least preferable option is to place the concentrator inside the internal network. With this type of design, if the concentrator is compromised, the attacker would have full access to the internal network, with no firewalls to inhibit their activities. With any of these designs, you will have to permit the required ports through the firewall and forward them to your VPN concentrator in order to ensure VPN access.

VPN Access: Protocols

Another consideration in providing VPN access is the type of VPN protocol you want to use. IPsec is still the most widely deployed VPN technology for good reason. One is interoperability. As a widely used and tested standard, IPsec will work with virtually any modern firewall and operating system. The disadvantage of IPsec is that it can sometimes be difficult to configure properly, and there is zero margin for error on the configuration. Both ends have to se the same parameters for encryptions, hashing, and so forth, or the tunnel cannot be established. SSL is an increasingly popular choice for VPNs, largely because of its simplicity to implement.

Once you have chosen a design and VPN technology, you need to consider the administrative ramifications of offering remote access. Some level of training will be required. At the very least, they may require training to use the VPN software. It is a good idea to educate your users on good security habits as well. A determination will also need to be made as to whether remote users are allowed to use their own personal computers and/or laptops, or if they must use a company-provided computer for remote access. The former option carries with it many risks. When a remote user connects their personal computer to the corporate network, they may have spyware, a virus, or any number or potentially damaging conditions present on their system. Due to the fact that you probably do not have any administrative access to their systems, you may have no way to secure the personal systems even if you wanted. This is why most companies require that only corporate resources be allowed to connect to the company network.

VPN Access: Hardware

One last consideration for VPN access is hardware selection. Normal workplace desktop applications place very little strain on even a remotely modern processor. The same is not true when it comes to VPN connections. A single VPN connection requires little overhead and rarely impacts the remote user’s system unless it is especially underpowered. For the VPN concentrator, however, it will handle the encryption and decryption of multiple connections, in addition to managing the volume of network data that will be accessed through it. For this reason, if you anticipate more than just a couple of VPN connections to be used simultaneously, you will want to test and evaluate your hardware needs.


Internal Links:

pfSense VPN: Part One

pfSense VPN: Part Two

pfSense VPN: Part Three (PPTP)

External Links:

An Overview of VPN Concentrators at YouTube (from CompTIA’s Network+ certification training)

How the VPN Concentrator Works at networkingtechnicalsupport.blogspot.com

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