How to configure Ubuntu 12.04 as a VPN server that allows connections from OS X and iOS?

Question

I am trying to setup a VPN using PPTP and connect using iPhone (iOS) but it fails.

May 25 22:43:38 zork pptpd[28793]: CTRL: Client x.x.x.x control connection finished
May 25 22:44:02 zork pptpd[28810]: MGR: connections limit (100) reached, extra IP addresses ignored
May 25 22:44:02 zork pptpd[28811]: MGR: Manager process started
May 25 22:44:02 zork pptpd[28811]: MGR: Maximum of 100 connections available
May 25 22:44:08 zork pptpd[28812]: CTRL: Client x.x.x.x control connection started
May 25 22:44:09 zork pptpd[28812]: CTRL: Starting call (launching pppd, opening GRE)
May 25 22:44:09 zork pppd[28813]: Plugin /usr/lib/pptpd/pptpd-logwtmp.so loaded.
May 25 22:44:09 zork pppd[28813]: pppd 2.4.5 started by root, uid 0
May 25 22:44:09 zork pppd[28813]: Using interface ppp0
May 25 22:44:09 zork pppd[28813]: Connect: ppp0  /dev/pts/5
May 25 22:44:09 zork pptpd[28812]: GRE: Bad checksum from pppd.

Answer 1

Solved the problem by editing: /etc/ppp/pptpd-options

# Encryption (comment other options in this section!)
require-mschap-v2
require-mppe-128

ms-dns 8.8.8.8
ms-dns 8.8.4.4

service pptpd restart