TweetFollow Us on Twitter

Virtual Private Networks

Volume Number: 21 (2005)
Issue Number: 3
Column Tag: Programming

Virtual Private Networks

by Brad Belyeu

Secure E-commuting

How to securely get to the office on the information super-highway

Introduction

Let's say your working on a big project at the office. Of course, the project is saved on the fileserver for security and accessibility reasons. The big deadline is Friday at five, and you or one of your team-members becomes deathly ill a couple days before. Or what if there was a blizzard? How in the world are you going to work on this project for your biggest client when you can't make it to the office? Create a virtual office! Using a virtual private network, you could access the network file, application, & print servers just as if you were there. When you connect to a VPN, it appears as though your computer sits right on the local network. Access is not as fast as physically being on the LAN, but when you can't be there it's the next best thing.

Defining VPN

VPNs (or Virtual Private Networks) come in many shapes and sizes. It has been a buzzword that is fairly ambiguous and has taken on different meanings over time. VPNs provide secure remote access to internal (private) networks over public networks, usually the Internet. The problem in defining VPNs has to do with its ambiguity. Virtually all networks are virtual in some sense of the word. I don't have a direct cable connection to all the Internet resources I use on a daily basis. But I get to those resources through a public network, and they are often located on someone else's private network. Besides, what one person considers private is often not private enough for someone else. VPNs can't be defined by any specific software protocols because there are several different common protocols that work effectively.

Virtual private networks can be hardware or software based. Using Mac OS X Server or a software application like VPN Tracker Server allows you to create a software VPN server, but most VPN servers are pieces of hardware external to your computer. VPN hardware is often included inside a firewall or router. For example, I use the Linksys WRV54G, which is an Internet connection-sharing router, wireless access point, VPN endpoint, & firewall all wrapped up in a single box. Cisco makes some very powerful VPN hardware for large networks. Most software servers are created for a one to one connection using client-server based technology.

There are two main types of VPNs and I will define them by the endpoints they connect. The first is the client to LAN (local area network) connection. A local area network is your private internal network. You normally use this connection for remote users to connect to a single office from anywhere with Internet access. This is useful for telecommuting. If you have employees that work in the field but need access to office databases, this is the type of VPN that you need. The other VPN type is LAN to LAN. This VPN type is usually used to connect the resources at two office locations so they look like a single LAN. This is often used when a company has a corporate location and other locations that need access to the corporate resources, or when resources are distributed across a couple of locations.

But Why?

When companies wanted to connect different office locations together before the Internet was widespread, they normally had to lease lines from a cable company to connect the locations. This kind of a network is referred to as a trusted VPN. This was a secure way to build a network since no one outside the buildings had access to the network as long as the cable company protected their switches, but it was also a very expensive way to share resources. With the advancement of the Internet, it became clear that using public lines instead of privately leased lines could connect offices much less expensively. But could a network over public lines be trusted for private (secure) communication? Because of the need to protect data, secure VPNs were developed. Secure VPNs use network protocols to encrypt data as it leaves the originating network and then decrypt it when it arrives at its destination. If you are using a combination of both trusted and secure VPN technology, it is referred to as a hybrid VPN.

VPN Protocols

PPP (point-to-point protocol) is a protocol that allows users to dial-up a connection to access the Internet. This connection is basically a VPN. You're using public telephone lines to access the Internet, but the access is insecure. Point-to-point tunneling protocol (PPTP) is a protocol developed by several companies but usually associated with Microsoft. Microsoft added it into every OS release since Windows 98. PPTP was built on PPP technology to create a "tunnel" allowing secure passage of information. PPP is the parent technology of PPTP, and PPTP couldn't exist without PPP. PPTP sends data in encapsulated PPP packets, which are then encapsulated within IP packets. Encapsulation allows you to send different protocols over IP. That means you can send more than just IP packets over the VPN. It's like wrapping presents. You normally use different kinds of wrapping paper for different occasions, Christmas paper, birthday paper, etc. PPTP can only deliver IP packets over the Internet, which would be like demanding a present be wrapped in Christmas paper to be delivered. But if it's really a birthday present, PPTP allows you to wrap the present in birthday paper, then wrap it in Christmas paper for delivery. After the packet is delivered, the packet header knows that it is really a birthday present and takes off the Christmas wrapping paper at its final destination. That is how you can send IPX or NetBEUI packets over IP with PPTP. The trick of PPTP being able to send other packets over IP lies in the fact that it runs at the OSI (open systems interconnection) layer 2, or link layer. PPTP relies on PPP for its authentication and encryption methods. PPTP can be used to create a 'tunnel' between two locations using TCP port 1723. Once the TCP connection is established, both control messages and data packets are sent from one endpoint to the other. These control messages do everything from initializing the VPN, to keeping it alive, and closing the VPN session. Control messages also serve other maintenance functions for the VPN. The weaknesses of PPTP are that it does not provide strong encryption for protecting data nor does it support any token-based methods of authenticating users.

L2TP (layer 2 tunneling protocol) combines the best features of PPTP and L2F from Cisco Systems into one protocol. The Internet Engineering Task Force (IETF) standardized L2TP for tunneling PPP across a public network. The main two components of L2TP are the Access Controller (LAC) and the Network Server (LNS). L2TP is similar to PPTP and runs over the OSI layer 2 so it can also route other protocols through IP packets. Data is forwarded from the LAC, which can be your own computer or your ISPs, to the LNS. If you're inside a private network, L2TP may be fine by itself. Because L2TP can't prevent packets from being changed, stolen, or faked, it is usually combined with IPSec when used across the Internet.

IPSec is the most secure way to connect to a VPN network. There are two components to IPSec: the authentication header (AH) and the Encapsulating Security Payload (ESP). The AH creates a special hashing algorithm and a specific key known only to the source and destination, which is used to check for packet integrity. A security association is setup between the devices and the AH stores the output of the special computation. Then the receiving device does the same computations, it checks the AH to make sure the computations are the same. This verifies that the packet has not been altered from its original state. It is a checksum type of authentication. The AH provides authentication but not privacy; the ESP does that by encrypting the data. The ESP encryption algorithm is a key known only to the source and destination so no one in-between can decrypt the transmitted data.

IPSec can run in two different modes. These modes relate to how IPSec is set up. If two routers are creating a VPN connection, it uses tunnel mode; but if the VPN is host to host, it uses transport mode. In transport mode, only the data portion of the packet is encrypted. To obtain maximum security, one should use tunneling mode where the entire IP packet is encrypted and authenticated. The only downfall of IPSec is that it runs on OSI layer 3 and only supports IP packets. There is a way to overcome this however. Bundling L2TP with IPSec allows a VPN with maximum security and multiple protocols. Because IPSec by itself has no way of tunneling, it is normally only used with L2TP. L2TP creates the tunnel and IPSec allows it to be secure. This is the most secure way to create a private network and is being adopted as the best standard. RFC 3193 describes the standard for bundling L2TP & IPSec. (http://www.faqs.org/rfcs/rfc3193.html)

OS 10.3 & VPNS

OS 10.3 Panther has built in VPN client support through the Internet Connect application (see figure 1). It currently allows for two different kinds of VPN connections: PPTP or L2TP over IPSec in transport mode.


Figure 1. VPN Connections

Apple doesn't allow for plain IPSec connections because, "Pure IPSec only provides user authentication or configuration of the client machine through protocols which are either proprietary or defined by the long-expired IETF drafts, which are not standards. Using PPP/L2TP over IPSec is the only "standard" way of doing remote access with user authentication and IP address assignment over IPSec at this time." (http://docs.info.apple.com/article.html?artnum=108088) What Apple means by "Pure IPSec" is using IPSec without the internal encapsulation. The built-in functionality of the VPN client for OS X is very limited, but there are good applications for expanding that functionality. VPN Tracker (http://www.apple.com/downloads/macosx/networking_security/vpntracker.html) is an excellent application for customizing your VPN connection. VPN Tracker is one of many products developed by equinux for VPNs. VPN Tracker allows you to customize every option of the connection (see figure 2). It also has built in support for a large number of VPNs from major vendors. If you choose the option for that specific VPN server, it will automatically set all the necessary options for you.


Figure 2. VPN Tracker

Equinux also makes a VPN Tracker Server in case you want to setup a VPN connection to a specific computer on your network. If you decide to setup a software VPN and you are behind a NAT (Network Address Translation) router, you need to make sure it has VPN pass-through enabled or the proper TCP/UDP ports are being forwarded.

Conclusion

Setting up a VPN can be complicated; but with the proper hardware & software, the average Macintosh user can do it. With all the different protocols, setup needs to be thought out before hand. If you choose a hardware router/VPN, research the manufacturers products first to see which protocols they work with. I've had no problem with my Linksys router, and I've setup other common brands that have worked as well (D-Link, Netgear, etc.) I would suggest viewing equinux's website at http://www.equinux.com/us/products/vpntracker/interoperability.html for a list of products that work with VPN Tracker. If you're going to use Internet Connect, it is very compatible with a large range of products; but doesn't offer near as much customization as VPN Tracker. I strongly suggest downloading and trying out equinux's VPN Tracker to keep those private networks secure!


Brad Belyeu is the President of ABConsulting based out of Oklahoma City, OK. He is an Apple Certified Technician and a member of the Apple Consultant Network.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Latest Forum Discussions

See All

Six fantastic ways to spend National Vid...
As if anyone needed an excuse to play games today, I am about to give you one: it is National Video Games Day. A day for us to play games, like we no doubt do every day. Let’s not look a gift horse in the mouth. Instead, feast your eyes on this... | Read more »
Old School RuneScape players turn out in...
The sheer leap in technological advancements in our lifetime has been mind-blowing. We went from Commodore 64s to VR glasses in what feels like a heartbeat, but more importantly, the internet. It can be a dark mess, but it also brought hundreds of... | Read more »
Today's Best Mobile Game Discounts...
Every day, we pick out a curated list of the best mobile discounts on the App Store and post them here. This list won't be comprehensive, but it every game on it is recommended. Feel free to check out the coverage we did on them in the links below... | Read more »
Nintendo and The Pokémon Company's...
Unless you have been living under a rock, you know that Nintendo has been locked in an epic battle with Pocketpair, creator of the obvious Pokémon rip-off Palworld. Nintendo often resorts to legal retaliation at the drop of a hat, but it seems this... | Read more »
Apple exclusive mobile games don’t make...
If you are a gamer on phones, no doubt you have been as distressed as I am on one huge sticking point: exclusivity. For years, Xbox and PlayStation have done battle, and before this was the Sega Genesis and the Nintendo NES. On console, it makes... | Read more »
Regionally exclusive events make no sens...
Last week, over on our sister site AppSpy, I babbled excitedly about the Pokémon GO Safari Days event. You can get nine Eevees with an explorer hat per day. Or, can you? Specifically, you, reader. Do you have the time or funds to possibly fly for... | Read more »
As Jon Bellamy defends his choice to can...
Back in March, Jagex announced the appointment of a new CEO, Jon Bellamy. Mr Bellamy then decided to almost immediately paint a huge target on his back by cancelling the Runescapes Pride event. This led to widespread condemnation about his perceived... | Read more »
Marvel Contest of Champions adds two mor...
When I saw the latest two Marvel Contest of Champions characters, I scoffed. Mr Knight and Silver Samurai, thought I, they are running out of good choices. Then I realised no, I was being far too cynical. This is one of the things that games do best... | Read more »
Grass is green, and water is wet: Pokémo...
It must be a day that ends in Y, because Pokémon Trading Card Game Pocket has kicked off its Zoroark Drop Event. Here you can get a promo version of another card, and look forward to the next Wonder Pick Event and the next Mass Outbreak that will be... | Read more »
Enter the Gungeon review
It took me a minute to get around to reviewing this game for a couple of very good reasons. The first is that Enter the Gungeon's style of roguelike bullet-hell action is teetering on the edge of being straight-up malicious, which made getting... | Read more »

Price Scanner via MacPrices.net

Take $150 off every Apple 11-inch M3 iPad Air
Amazon is offering a $150 discount on 11-inch M3 WiFi iPad Airs right now. Shipping is free: – 11″ 128GB M3 WiFi iPad Air: $449, $150 off – 11″ 256GB M3 WiFi iPad Air: $549, $150 off – 11″ 512GB M3... Read more
Apple iPad minis back on sale for $100 off MS...
Amazon is offering $100 discounts (up to 20% off) on Apple’s newest 2024 WiFi iPad minis, each with free shipping. These are the lowest prices available for new minis among the Apple retailers we... Read more
Apple’s 16-inch M4 Max MacBook Pros are on sa...
Amazon has 16-inch M4 Max MacBook Pros (Silver and Black colors) on sale for up to $410 off Apple’s MSRP right now. Shipping is free. Be sure to select Amazon as the seller, rather than a third-party... Read more
Red Pocket Mobile is offering a $150 rebate o...
Red Pocket Mobile has new Apple iPhone 17’s on sale for $150 off MSRP when you switch and open up a new line of service. Red Pocket Mobile is a nationwide MVNO using all the major wireless carrier... Read more
Switch to Verizon, and get any iPhone 16 for...
With yesterday’s introduction of the new iPhone 17 models, Verizon responded by running “on us” promos across much of the iPhone 16 lineup: iPhone 16 and 16 Plus show as $0/mo for 36 months with bill... Read more
Here is a summary of the new features in Appl...
Apple’s September 2025 event introduced major updates across its most popular product lines, focusing on health, performance, and design breakthroughs. The AirPods Pro 3 now feature best-in-class... Read more
Apple’s Smartphone Lineup Could Use A Touch o...
COMMENTARY – Whatever happened to the old adage, “less is more”? Apple’s smartphone lineup. — which is due for its annual refresh either this month or next (possibly at an Apple Event on September 9... Read more
Take $50 off every 11th-generation A16 WiFi i...
Amazon has Apple’s 11th-generation A16 WiFi iPads in stock on sale for $50 off MSRP right now. Shipping is free: – 11″ 11th-generation 128GB WiFi iPads: $299 $50 off MSRP – 11″ 11th-generation 256GB... Read more
Sunday Sale: 14-inch M4 MacBook Pros for up t...
Don’t pay full price! Amazon has Apple’s 14-inch M4 MacBook Pros (Silver and Black colors) on sale for up to $220 off MSRP right now. Shipping is free. Be sure to select Amazon as the seller, rather... Read more
Mac mini with M4 Pro CPU back on sale for $12...
B&H Photo has Apple’s Mac mini with the M4 Pro CPU back on sale for $1259, $140 off MSRP. B&H offers free 1-2 day shipping to most US addresses: – Mac mini M4 Pro CPU (24GB/512GB): $1259, $... Read more

Jobs Board

All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.