Hi we have implemented a microtic routerboard that does a vpn dialup from south africa to london , the problem is that when the pptp interface is enabled the vpn connection only stays up for about 2 minutes , sometimes longer. The only way i can get the pptp connection to stay up is by resetting the pptp interface and running a constant ping to the london ip address. Any ideas or help on this please? 
what you have on second end (on first you have RouterOS)
and check if there are not any idle timeout set on other end.
Hi , thanx
I have a freaking windows 2003 server here in Joburg and they have a server 2003 in london , so i need multipale connections to the vpn to london from one ip here in joburg.
Still running a constant ping to keep the connection up. 
and where is that RB with RouterOS? 
check server settings - if there is any idle timeout mentioned disable that, i had no problems creating VPN tunnel from PC (linux) to RouterOS
pleas be careful with settings you set on your server
EDIT:
you can set ICMP packet size to a smaller one so you will not feel any impact of that ping going in background
Basicly i have the windows 2003 server here in joburg , that connects to the routerboard that does my adsl dialup aswell , so from it i do the vpn dialup to london vi the adsl line to connect to their server there. 
is there anything in logs in ROS box?
set up logging of pptp tunnel and check out - what is happening when you cannot/disconnect
sounds like a NAT or firewall timeout in between your routeros and the windows 2003 server.
What i have done now is i created the following script
:if ([/ping $n size=28 count=5] = 0) do {
:log info “0 replys disabling interface…”
/interface pptp-client dis [find name=“pptp-client1”]
:log info “interface disabled. Waiting 5 sec.”
elay 5
:log info “enabling interface…”
/interface pptp-client enable [find name=“pptp-client1”]
:log info “interface enabled”
elay 6
:global n [/ip address get [find interface=pptp-client1] network]
}
So this is checking the connection every 30 seconds now.
Cool script, i’m sure it will help someone who searches the archives in the future. Scripts are sometimes necessary to add more intelligence in a network.
I would probably have used / tool netwatch and increased the interval (in case of random packet loss). Setting pptp-client’s disabled=no (even if it already is set as disabled=no) would make it reconnect and thus you don’t have to worry much about potential synchronization issues.
EDIT:
When using netwatch i would have used “/ ping” to verify that it was actually down (netwatch is a little too sensitive)