Question : ISA PPTP VPN connection not working

Hello, I have had my ISA server running and accepting VPN connections for years. A week ago, it stopped accepting VPN connections for no apparent reason.

No changes were made, on both our network, and on our hosted firewall.

Now, whenever someone connects, ISA spits out the error:

Event Type:      Warning
Event Source:      Rasman
Event Category:      None
Event ID:      20209
Date:            20/05/2010
Time:            10:16:11 AM
User:            N/A
Computer:      ISA
A connection between the VPN server and the VPN client has been established, but the VPN connection cannot be completed. The most common cause for this is that a firewall or router between the VPN server and the VPN client is not configured to allow Generic Routing Encapsulation (GRE) packets (protocol 47). Verify that the firewalls and routers between your VPN server and the Internet allow GRE packets. Make sure the firewalls and routers on the user's network are also configured to allow GRE packets. If the problem persists, have the user contact the Internet service provider (ISP) to determine whether the ISP might be blocking GRE packets.

For more information, see Help and Support Center at

I have gone through this with our provider, and they assure me GRE packets arent being dropped at their end. Nothing has changed with our router, so I dont really know how to approach this issue.

I found the W2k3 SP1 issue on the MS site, and tried installing the patch, even though our server is SP2 now.

Anyone have any idea how this could just happen?


Answer : ISA PPTP VPN connection not working

Hi Just had a look at one of our ISA servers - looks like when a connection comes through there are GRE packets as well.
Perhaps a good idea to ask the hosted firewall people if they allow GRE through?
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