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Virtual Private Networks¶
VPNs provide a means of tunneling traffic through an encrypted connection, preventing it from being seen or modified in transit. pfSense® software offers three VPN options: IPsec, OpenVPN, and L2TP. This chapter provides an overview of VPN usage, the pros and cons of each type of VPN in pfSense, and how to decide which is the best fit for a particular environment. Subsequent chapters discuss each VPN option in detail.
L2TP is purely a tunneling protocol and does not offer any encryption of its own. It is typically combined with some other method of encryption such as IPsec in transport mode. Because of this, it doesn’t fit in with most of the discussion in this chapter. See L2TP VPN for more information on L2TP.
PPTP server support has been removed from pfSense software. Despite the attraction of its convenience, PPTP must not be used under any circumstances because it is no longer secure. This is not specific to the implementation of PPTP that was in pfSense; Any system that handles PPTP is no longer secure. The reason for the insecurity is that PPTP relies upon MS-CHAPv2 which has been completely compromised. Intercepted traffic can be decrypted by a third party 100% of the time, so consider any traffic carried in PPTP unencrypted. Migrate to another VPN type such as OpenVPN or IPsec as soon as possible. More information on the PPTP security compromise can be found at https://isc.sans.edu/diary/End+of+Days+for+MS-CHAPv2/13807 and https://www.cloudcracker.com/blog/2012/07/29/cracking-ms-chap-v2/.
There are four common uses of the VPN capabilities of pfSense, each covered in this section.
Site-to-site connectivity is primarily used to connect networks in multiple physical locations where a dedicated, always-on, connection between the locations is required. This is frequently used to connect branch offices to a main office, connect the networks of business partners, or connect a network to another location such as a data center environment.
Before the proliferation of VPN technology, private WAN circuits were the only solution to connect multiple locations. These technologies include point-to- point dedicated circuits, packet switching technologies such as frame relay and ATM, and more recently, MPLS (Multiprotocol Label Switching) and fiber and copper based metropolitan Ethernet services. While these types of private WAN connectivity provide reliable, low latency connections, they are also very costly with recurring monthly fees. VPN technology has grown in popularity because it provides the same secure site to site connectivity using Internet connections that are generally much less costly.
Limitations of VPN connectivity¶
Performance is an important consideration when planning a VPN solution. In some networks, only a private WAN circuit can meet the requirements for bandwidth or latency. Latency is usually the biggest factor. A point to point DS1 circuit has end to end latency of about 3-5 ms, while the latency to the first hop on an ISP network will generally be at least that much if not higher. Metro Ethernet services or fiber circuits have end to end latency of about 0-3 ms, usually less than the latency to the first hop of an ISP network. That will vary some based on geographical distance between the sites. The stated numbers are typical for sites within a couple hundred miles of each other. VPNs usually see latency of around 30-60 ms depending on the Internet connections in use and the geographical distance between the locations. Latency can be minimized and VPN performance maximized by using the same ISP for all VPN locations, but this isn’t always feasible.
Certain protocols perform very poorly with the latency inherent in connections over the Internet. Microsoft file sharing (SMB) is a common example. At sub-10 ms latency, it performs well. At 30 ms or higher, it’s sluggish, and at more than 50 ms it’s painfully slow, causing frequent hangs when browsing folders, saving files, etc. Getting a simple directory listing requires numerous round trip connections between the client and server, which significantly exacerbates the increased delay of the connection. In Windows Vista and Server 2008, Microsoft introduced SMB 2.0 which includes new capabilities to address the issue described here. SMB 2.0 enables the sending of multiple actions in a single request, as well as the ability to pipeline requests, meaning the client can send additional requests without waiting for the response from prior requests. If a network uses exclusively Vista and Server 2008 or newer operating systems this won’t be a concern, but given the rarity of such environments, this will usually be a consideration. SMB 3.0 further improves in this area with support for multiple streams.
Two more examples of latency sensitive protocols are Microsoft Remote Desktop Protocol (RDP) and Citrix ICA. There is a clear performance and responsiveness difference with these protocols between sub-20 ms response times typically found in a private WAN, and the 50-60+ ms response times common to VPN connections. If remote users work on published desktops using thin client devices, there will be a notable performance difference between a private WAN and VPN. Whether that performance difference is significant enough to justify the expense of a private WAN will vary from one environment to another.
There may be other network applications in an environment that are latency sensitive, where the reduced performance of a VPN is unacceptable. Or all locations may be within a relatively small geographical area using the same ISP, where the performance of a VPN rivals that of private WAN connections.
Remote access VPNs enable users to securely connect into a network from any location where an Internet connection is available. This is most frequently used for mobile workers (often referred to as “Road Warriors”) whose job requires frequent travel and little time in the office, and to give employees the ability to work from home. It can also allow contractors or vendors temporary access to a network. With the proliferation of smart phones, users have a need to securely access internal services from their phones using a remote access VPN.
Protection for wireless networks¶
A VPN can provide an additional layer of protection for wireless networks. This protection is two-fold: It provides an additional layer of encryption for traffic traversing the wireless network, and it can be deployed in such a way that it requires additional authentication before access to network resources is permitted. This is deployed mostly the same as remote access VPNs. This is covered in Additional protection for a wireless network.
Remote access VPNs can be configured in a way that passes all traffic from the client system over the VPN. This is nice to have when using untrusted networks, such as wireless hotspots as it lets a client push all its Internet traffic over the VPN and out to the Internet from the VPN server. This protects the user from a number of attacks that are possible on untrusted networks, though it does have a performance impact since it adds additional hops and latency to all connections. That impact is usually minimal with high speed connectivity when the client and VPN server are relatively close geographically.