iPad, iPhone, and Mac OS X L2TP/IPsec VPN to Windows Server 2008 R2

I spent quite a while experimenting with L2TP over IPsec with my iPad 2, and surprisingly found no useful guides as to how to configure it. Judging by what I could find online, most people simply give up and use PPTP instead which has significant security vulnerabilities. Here’s a concise comparison of PPTP versus L2TP/IPsec which describes that weakness:
http://www.ivpn.net/pptp-vs-l2tp-vs-openvpn.php

I had considered using Apple’s support for Cisco IPsec but that would have meant exposing the core switch where I work. It’s old enough to make that a bad idea. The Juniper Netscreen firewall only supports L2TP with certificates and not Pre-Shared Key so that was also ruled out. This post will outline how to configure Windows Server 2008 R2’s NPS/RRAS role to host L2TP/IPsec connections which will allow iPads and iPhones to connect securely into your Windows infrastructure without the need for additional client software.

Firstly, it’s likely that your NPS/RRAS server is behind a perimeter firewall. If this is the case you’ll need to grant IPsec traffic access from the public internet. Using details from this Technet post I created the following custom service object on the Netscreen firewall, and allowed it inbound to the RRAS server (IP protocols 50 and 51, UDP 500 and 4500). For initial testing though you should probably create a rule to allow all traffic to and from your test client.

IPSec service definition

I am going to assume a knowledge of both NPS and RRAS. For more information on those, other guides exist. As far as I have been able to discover, it seems that the iPad only supports Pre-Shared Key authentication for the IPsec tunnel, rather than certificates-based. The VPN connection settings GUI in Mac OS 10.6 for instance will allow either method, but not in iOS. It may be possible to force your way around this with the iPhone Configuration Utility (designed for applying corporate settings to iOS) but information is pretty scant. I did find a long forum thread about certificate auto-enrollment, and a Microsoft Directory Services team blog post, but I suspect they may relate more to 802.1x:
https://discussions.apple.com/message/10402090
http://blogs.technet.com/b/askds/archive/2010/11/22/ipad-iphone-certificate-issuance.aspx

The L2TP/IPsec Pre-Shared Key is configured by right-clicking on the top level of Routing and Remote Access in Server Manager -> Properties -> Security tab:
Pre-Shared Key for IPsec tunnel

It’s useful to keep your VPN clients on a different subnet to your servers, however multihoming with several NICs can cause problems, particularly if your RRAS server is also a Domain Controller. You can define a subnet for this purpose in the IPv4 tab here, but you will need to remember to add a static route entry on your router pointing traffic for this subnet to the RRAS server.

RRAS client subnet settings

In Server Manager -> NPS -> Policies -> Network Policies create a policy with the following settings, making sure to set the encryption settings. As this Microsoft KB article makes clear, these options actually ensure that IPsec gets used, with the different grades here representing different algorithm proposal combinations. The iPad supports the maximum encryption setting.

NPS Policy Settings for L2TP/IPSec

Lastly, the Mac OS X and iOS VPN client configuration is pretty self-explanatory. Make sure to use the Pre-Shared Key that you defined on the RRAS server (referred to here as Secret):

iPad L2TP VPN configuration

I would at this point like to thoroughly recommend iTap RDP as being the best iOS Remote Desktop client I have seen. It has NLA authentication support, a universal iPad/iPhone binary, and by far the most intuitive controls which really puts it ahead of the competition.

UPDATE – I was hoping to use this VPN configuration for all clients, but it seems that Mac OS clients cannot connect. Mac OS apparently didn’t use the standard L2TP UDP port 1701. Someone compiled a fix for Snow Leopard but I could not get it to work. It’s possible that this is all out of date information though.

UPDATE 2 – I did some more troubleshooting from home and discovered that when a tunnel is initiated from a second device on my home network while another tunnel is already up, all further connection attempts then fail for a long while, even when the RRAS server is rebooted. This would suggest that the Netscreen firewall at my work still considers the original session open, and thus it will eventually timeout after 30 minutes. This behaviour had disrupted my Mac OS X test results. Using verbose logging on the Mac and looking at the NPS log I could see that Mac OS X 10.6.8 VPN client does not accept the 128bit encryption setting. Permitting 56bit encryption allows Macs to connect, but perhaps older versions of Mac OS could have difficulties. I have updated the policy settings screenshot above.

UPDATE 3 – I realised that although NATed clients could connect, clients with public addresses could not. I have amended the destination ports for IP protocols 50 and 51 in the firewall IPsec definition screenshot (it had defaulted to 0-0 rather than 0-65535 for some reason). I have verified that this VPN works for Windows XP clients, Windows 7, Mac OS X 10.6, and Mac OS X 10.5, as well as iPhones (mine’s on iOS 3.1.3) and iPads. Once connected to the RRAS server you cannot interact with that server directly, so make sure that the RRAS server’s own DNS settings do not refer to itself as a primary (assuming it’s also a DNS server) – these DNS entries will be inherited by all VPN clients.

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6 thoughts on “iPad, iPhone, and Mac OS X L2TP/IPsec VPN to Windows Server 2008 R2

  1. Mathijs

    Thanks a lot for this post. As long as Apple doesn’t support OpenVPN, this will help me through.

    Reply
  2. acfkevin

    Out of curiosity, why MS-CHAP v2 instead of EAP-MS-CHAP v2? I was thinking the latter was a default out of the box, and that you had to intentionally tick off vanilla “MS-CHAP v2″ under a scary warning about “these authentication methods are less secure” in the RRAS manager. That Microsoft themselves would tell you it’s “less secure” right on the config page gives me pause about using it.

    I’m desperately seeking some definitive reference on the web that tells me whether or not EAP-MSCHAP v2 is supported on Leopard (10.5)—or iOS for that matter. Google has not been forthcoming with this information. We know that plain MSCHAP v2 works fine for these OS X clients, and Ubuntu Lucid Lynx (10.04).

    Wondered if you had just determined this on your own out of trial-and-error (as we had to) or if you’d found a reference that stated that the less-secure MSCHAP v2 needed to be enabled for Mac OS X (or in your case, iOS) clients.

    Cheers!

    Reply
    1. patters Post author

      It’s been a while since I looked at this, but I think the Mac OS/iOS integrated VPN client only support MS-CHAP v2. And Apple will always claim they’re ahead of the competition…

      Reply
      1. acfkevin

        Doesn’t help that a web search for “mac os x eap-mschap” turns up… um, nothing very helpful at all. At least that doesn’t pertain to 802.1x, which I want nothing to do with.

        Is EAP-MSCHAPv2 in a PPTP context the same as what Wikipedia calls PEAPv0? Wonder if I’d have more luck searching for “mac os x pptp peapv0″…

        I see “EAP” tokens in the pppd logs on a Leopard client, but I don’t know whether to interpret that as equating to “EAP-MSCHAP v2″ support. Time to hit up the Apple “support community.” That ought to be fun.

  3. mtn_lion

    Brilliant article, thanks so much for the clear/complete explanation. I need to connect a mix of Windows, Mac and iOS clients to Server 2008r2, want to keep things as simple as possible–i.e., one VPN technology. Woulda prefered pure IPSec, but we don’t have Cisco. Your article confirmed that L2TP is what the clients all have in common, natively–and showed me exactly how to do it.

    Reply

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