Building Linux Virtual Private Networks

Richard Miller contributed this review of New Riders' entry to the field of VPN books. No suspense, he gives the book a big thumbs up -- read on below for his reasoning, in particular a comparison to the previously available alternatives. Building Linux Virtual Private Networks author Brian Hatch, Oleg Kolesnikov pages 408 publisher New Riders rating 10 reviewer Richard Miller ISBN 1578702666 summary Finally, a VPN book you can use.

Rants

I've been on the lookout for a good VPN book since I first bought the O'Reilly VPN book in 1998. Yes, that book shattered my long standing belief that O'Reilly could do no wrong. The technical descriptions of VPN technologies were flawed and confusing, and they seemed to think that the only usable VPN technologies were commercial products. They only showed you implementations via screen shots of point-and-click GUI sessions. The one potentially portable section describing PPP over SSH was practically copyright infringement from the HOWTO, but with enough errors that they could make the case they had never actually read it.

For a while the O'Reilly VPN book was the only one out there. Then a few other publishers got into the mix. Unfortunately their results were no better. I could never find a book that had both a description of the protocols that would allow you to debug problems and implementation details that weren't so vague that they could apply to the installation of my washing machine. I must have bought half a dozen VPN books, all of which were severly lacking in crucial aspects that would make them usable. I had little stickies placed in them showing me which parts were correct and helpful, and would flop between them all whenever I needed to do something, because nothing got it all right.

Now I'm not here just to flame these other books, but I must let you get an idea for how I was feeling, because only then can you understand how much happier I am now. Now I can finally throw away all those other books.

Building Linux VPNs was written by Brian Hatch (of Hacking Linux Exposed fame) and Oleg Kolesnikov, and published by the New Riders, the same guys who do the SANS publications. It's not as thick as you might expect, coming in at 408 pages, but it's remarkably dense in a good way. No wasted space for boring screen shots, instead concentrating on well tailored diagrams when needed, code listings, and command line sessions.

Overview

Part one, the first two chapters, teaches you everything you need to know about general VPN technology, and discusses all the VPN issues you're going to face: various different network topologies you could use, how to get your routing set up on both servers and clients, DNS setups, how to use VPNs with firewalls (and where they could go) and more. These are the issues that the trickiest to get right when actually setting up a VPN, and something most other VPN books leave up to the reader to figure out.

Part two discusses standard VPN protocols. The first two chapters of this section discuss creating a VPN with PPP over SSH and SSL. For those of us who have implemented PPP over SSH following the HOWTO before, you'll remember how hackish it felt. The authors have come up with a much more modular (you can have any number of VPNs easily) and secure (they teach you how to set up your SSH keys or SSL certificates securely) method, and provide you all the code to do it. Following the step-by-step instructions, you could make a PPP over (SSH/SSL) VPN in about 30 minutes. Rock on.

They then dedicate two chapters to IPSec: one for the description of the protocol itself (which definitely deserves a chapter) and then one for the implementation of FreeS/WAN. IPSec is known to be a difficult beast to ride, and they do a really great job of giving you the information needed to get it right.

The last chapter of this part covers PPTP for both server and client. I was shocked to see PPTP discussed in a Linux book, but I guess the authors say it best when they said:

"There are times when you must support PPTP, either because you are forced to connect to a server that only runs PPTP or because you need to support remote Windows machines. In either of these cases, we offer our deepest sympathies."

Part three discusses non-standard VPN protocols. In the same detailed fashion, the authors devote three chapters to alternative VPN technologies VTun, CIPE, and tinc. While these technologies do not have IETF protocol drafts, they are nonetheless well defined, and work on multiple Unix platforms.

Analysis

In this day and age of '2nd/3rd/4th Edition' it's good to see a book that really hit the nail on the head the first time. Building Linux Virtual Private Networks has all the technical information you need to understand the protocols, set up your networks, and troubleshoot, and has the implementation details to get it all done almost entirely pain free.

It's extreemly easy to read, has a consistent style and tone, and uses just the right amount of humor to keep you interested in something that could be an extreemly boring technical topic.

One nice thing is that they defined their network early in the book, and they implemented each separate VPN technology using the same network, including host names, IP addresses, etc. This consistency really pays off in clarity to the reader.

Beefs

There's a good bit of code in the book, which is a great thing. They mention throughout that you can download the code online at their website, but it doesn't seem to be there yet. Hopefully this will get rectified. (You can still get a preview, though, at the book's official website. Good to see folks who don't blindly use ".com" for everything. )

Also, a lot of the software they discuss works on *BSD, Solaris, some even on Windows. Why does every book need to include the magic 'L' word in the title nowadays?

Kudos.

You can purchase Building Linux VPNs from Fatbrain. Want to see your own review here? Just read the book review guidelines, then use Slashdot's handy submission form.

Comments

Re:What's complicated about FreeSWAN?

[Starship Trooper]

What's complicated about FreeSWAN?

Well, a LOT. Not if you're deeply involved technically in the project, but if you back out and take the perspective of someone who's never used a VPN, plenty.

A lot of people don't even think about the fact that there's a separate protocol field in IP, or that people run any IP protocol but UDP or TCP. Getting 50/51 through your existing firmware firewall can be a real trick. FreeSWAN requires you to be able have the GNU Multi-Precision library installed for the crypto calculations before you compile it. Unless your distro can with FreeSWAN, you have to recompile your kernel with modifications.

And, like many tools, there's no single graphical GUI; unlike SAMBA's excellent SWAT, there's nothing to lead you to ipsec.conf or ipsec.secrets. There's a LOT of reading to be done.

Ok, so, for you or me, it's easy. Maybe a day of reading tops. But compare that to the commercial world where an application must install and be configured from a GUI in a few hours, and FreeSWAN is... nearly a toy. It's unusable in a business environment. As soon as you say "compile", a CTO is going to turn down your volume.

It's cool, but don't call it uncomplicated. That's part of it's coolness (-;

The main problem with IPSEC...

[Junta]

IPSEC is wonderful, but many businesses don't think things through and use it for telecommuting. Why is this bad? Well, the way this works is that someone connects to the VPN system and gets a full tunnel that allows the authorized client to behave on the internal network as if it was actually there, bypassing the firewall. The problem here is pretty obvious. The client machine is not protected by a firewall,a nd so if the client is compromised, an attacker has a clear path straight past the firewall. So the effectiveness of the firewall is greatly reduced.

Now if you don't have a firewall protectecting the network, this won't hurt, but if you do, then a solution like ssh is somewhat more secure, as you only set up the tunnels you absolutely need to very specific hosts. While there is still a risk, it is greatly reduced and strikes a good balance between usability and security.

What IPSEC *is* good for is seamlessly connecting sites together without really expensive dedicated lines securely. While it makes no guarantee as to bandwidht or availability, it does provide almost the same level of security. If a company can't afford lines to sites but still wants to expand, IPSEC is ideal. I use it to connect my home private network to a friends home private network. The key here is that not only do you have to trust the clients whose keys you permit to connect, but you must also trust that the administrator of that client machine or network is sufficiently competent to keep his network secure, as the security of the two networks is tied a lot more closely together...