Securing 802.11b with PPPoE?

no free lunches asks: "After giving up in disgust on layer 2 auth like *EAP/802.1x (which is a nightmare to configure properly and requires expensive access points and bleeding edge - flaky - firmware) I am considering controlling access to my wireless LAN (a small 50-user setup, with only one Linux user - me) using PPPoE, and would like to ask the Slashdot crowd their opinion."

So far, the issues can be summarized as follows:

Advantages:

• Totally platform, NIC and AP independent - you can use any NIC, any OS, any access points.
• No IP addresses required on the PPPoE server or the APs - no DHCP, no nothing, so there is no easy way to have access without establishing a PPPoE session.
• Built-in crypto per session - using CHAP for auth and MPPE for data encryption.
• No client/proprietary auth software required on Windows XP (around 40 of my users, and the ones that will actually use this)
• Full session control (IP address assignments, traffic accounting, sessions only allowed during office hours, etc.), same as any remote access server.
• Cheap (server packages available for Linux and FreeBSD, any box can take the load)
• No proprietary IPSec tricks required - yes, I've considered it as an option, but remember, my users are Windows users, and PPPoE has the advantage of removing all IP addresses from the WLAN segment.

Disadvantages:

• No PPPoE clients for PDAs (yet)
• No published HOWTOs on PPPoE server setup under Linux (plenty of DSL/PPPoE client info and at least one HOWTO for FreeBSD, but since PPPoE servers are mostly commercial products, no one wants to give away info for free)
• MPPE encryption has some religious detractors (but it works fine for 98% of my users - the 49- strong Windows laptop crowd - and totally removes the need for WEP key management)
• Rogue PPPoE Servers - not really an issue if you can filter PPPoE frames on the radio interface - and I can, so you need wired access to set up one - but I'd like to know people's opinions on whether this is more than an urban myth fanned by 802.1x proponents.
• Freeloaders can still use the WLAN (even though there are no IP addresses) as a bridged segment (but I can sniff on the PPPoE server interface and/or poll every AP and kick out/ban any MAC addresses without an established PPPoE session - so MAC spoofing is of very limited use).

Mind you, the usual procedures apply (disabling SSID broadcast, changing MTUs for PPPoE, investigating other data encryption methods) so on and so forth, but this approach strikes me as being quite 'clean', cheap and, most important of all, easy to implement NOW instead of waiting for the 802.1x crowd to get their act together (sure, some people will say you can get usable 802.1x now, but my experience with six different vendors indicates that full interoperability is a joke, and that you need all sorts of proprietary items and tweaks - you either use a single vendor for everything, or you're bust).

I know some ISPs are already doing this and I'm sure there are some people with PPPoE knowledge out there, so I'd like to know about similar experiences."

Comments

NoNO

[Anonymous Coward]

pppoe is crap for your security. Don't use it and thinks you are safe.
Use IPSec or some VPN solution. e.g. tinc - tinc.nl.linux.org, available for most unices with a TUN/TAP driver.

Re:NoNO

[Anonymous Coward]

IPSec is (quickly becomming) the right way, especially when you are in a heterogeneous environment. Just don't fall into the trap of vendor specific extensions, like user/password based authentication. IPSec is not yet the univeral and easy solution it needs to be for widespread adoption, but the pieces are falling into place. SDNS is one large missing part of the puzzle which could make IPSec plug&play, but even without that, it is not very hard to use.

Ipsec Tricks?

[Ashran]

WinXP Supports IPsec out of the box. (Okay, you have to install the support tools from the WinXP CD, but thats it)
http://www.natecarlson.com/linux/ipsec-x509.p hp

I've setup an Linux IPsec GW for WinXP with dhcp a few days ago .. works like a charm.
(Using the x509 patch of course)

Re:Seperate Network and VPN?

[sporty]

Because your DHCP server becomes vulnerable, since it does everything in a non-encrypted protcol, where as with PPP, everything is encrypted.

'sides, you can DOS a dhcp server by taking all IP's possible.

More Hassle Than It's Worth

[alexpage]

Really. I looked into PPPoE and it's pretty nasty. I recently set up a wireless network for a company in Birmingham and found that the easiest thing to do was just use IPSec - Linux supports it, FreeBSD supports it, Win2K and XP support it. Set up one Linux or BSD box as an access point (note that you don't want ad-hoc mode for this) and use either shared secrets for each node or keypairs - that's an easy sneakernet install. If you want you can do clever things with your firewalling so systems without keys or secrets can get onto your network and abuse your network connection.

There's plenty of IPSec and 802.11b HOWTOs out there, and they're pretty useful - just make sure you're using a recent version of racoon, the *nix IKE daemon, and you should be fine.

Re:Seperate Network and VPN?

[Zack]

The only thing the DHCP server does is hand out IPs. That's it. After that the connection is done over a VPN which is all encrypted.

And you can DOS anything. Just flood the 802.11 spectrum with crap and nothing will work.

Re:Seperate Network and VPN?

[Zack]

Only if you use the same machine to do both internal and wireless DHCP. That's why the two networks are kept completely seperate, connected only by what we'll call the "wireless gateway"

So the "wireless gateway" hands out IPs to the wireless folks (in a different range from the internal network) and acts as the VPN router for the wireless. That's all that box should do. Then it has no effect on the internal network except for routing authorized network traffic.

Re:Try PPTP

[DA-MAN]

To get encryption going, you will need to install a couple of patches.

1) The kernel patch for ppp w/ mppe support 2) pppd patch for encryption support

check out this link

Works for me

[Dan Sisson]

I work for an ISP that sells broadband wireles. In designing our network, I chose to use almost the exactly same setup as you described. PPPoE gives us a lot more flexibility than any other access control method. You can back it with RADIUS for simple user management, and there are a lot more client solutions out there, ranging from free to licensed. We've been running with few problems for over 6 months now with our current hardware setup. I'd suggest checking out MikroTik RouterOS. It's a linux-based OS that supports everything mentioned thus-far in this thread.. from PPPoE to PPTP and even IPsec. You can even toss a pci/pcmcia card in it and make it an access point which removes another device from the network.