PPTP over cellular network with iPhone 3GS

ever since I upgraded my iPhone to OS3.0, I’ve been having trouble trying to get PPTP VPN to work. Never had the time to seriously look at it until now.

My VPN end point is a Linksys WRT54GL running with DD-WRT. I know that PPTP service works there as I can connect with my notebook, even with my 3G dongle.

Initial findings pointed towards the support for encryption on the DD-WRT implementation, and it has to be forced to “none” on the iPhone. Even that didn’t work.

With the release of OS 3.1, I started to tether my notebook to the iPhone, and through that, the PPTP will fail. That stumped me! Initially I thought could be due to the NAT implementation to enable tethering.

With trial and errors, I found out that over a WIFI connection, PPTP connection will work. Did I forget to mention that CISCO based IPSEC VPN to my office network works nicely over cellular and WIFI? That really baffled me. So, there’s something that’s in place that only works for IPSEC over cellular.

Finally, I came across some forum postings that lead me to the solution. There are many other people with similar issues in Canada and USA, and for some, they are able to tweak their APN on the phone to a different one and it worked for them. Of course they needed to be on different data subscription etc… for that to work.

I’m in Singapore, and my cellular provider is SingTel. I whipped out my iPhone 3GS and compared it’s APN settings to my 3G dongle for my notebook. Wallah! they are different, even though they are both with SingTel. I swapped in the new APN settings on to the iPhone, and PPTP started to work.

So, for all those in Singapore and on SingTel with similar needs and issues, the solution is to change the APN from “e-ideas” to “internet”. And here’s SingTel’s official instructions. BTW, these instructions are generic for all data devices.

For everyone else, what I realize from this is that some services/ports are controlled by the service provider. So, just by changing the APN won’t work if you don’t have access to the relevant APN.

If you need some guide on how to set your APN on your iPhone, the official Apple guide is found here.

*update 2009 Oct 09* after changing the APN, the “tethering” feature disappears. But if I reset the “Cellular Network” settings, “tethering” comes back. Got to figure out how to enable both.

4 thoughts on “PPTP over cellular network with iPhone 3GS

  1. hip

    What is the solution? I am in the same situation as you were before. Please share how you achieved to connect to PPTP VPN while tethering?

    Reply
    1. Jason Post author

      hello hip, the solution is to create a policy to change the APN of the iPhone via iPhone Configuration Utility, then push it to your iPhone. I found by doing that, we will not lose the tethering ability, and still be able to use PPTP VPN.

      Reply

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