Core issue
This Virtual Network Computing (VNC) over Point-to-Point Tunneling Protocol (PPTP) issue occurs when remote Windows clients initiate PPTP and use VNC to the PPTP (server). Other applications work fine over PPTP. However when VNC is used the PPTP tunnel goes down intermittently.
Debugs such as the Virtual Private Dialup Network (VPDN) and Point-to-Point Protocol (PPP) reveal that when this event occurs, the PPTP router-side tunnel goes down but the client does not see the PPTP tunnel as down. At this time, all router functions apart from VPDN to the problem client are normal. For example, other PPTP client connections are normal. Also, at this time, the "problem" PPTP client can function normally in all respects except for access to the remote PPTP server.
Resolution
In order to resolve this issue, perform this workaround for the PPTP connection.
On the virtual-template interface terminating the PPTP sessions, configure these commands:
Hostname(config)#interface Virtual-Template < 1 >
Hostname(config-if )#no ppp iphc
