Cisco 2821 GRE Problems

Unanswered Question
Jul 9th, 2009

I currently have a remote XP client trying to access our new vpn network from a remote location. The XP client is behind an at&t u-verse router. The flow diagram is below. I currently get a message on the XP client that GRE is not enabled or something of the sort, and it gets stuck on username and password verifying.

Flow Chart:

XP computer (


AT&t u-verse router (public ip)




Linksys RV082(, public ip) configured with VPN passthrough enabled and portfowarded to allow pptp


Cisco 2821(, port fowared to allow pptp


Windows XP VPN server(

Yes i do know that the 2821 can do vpn however I was asked to do it this way.

How would i configure the 2821 (firewall is enabled) and what eles may need to be changed.

I have this problem too.
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Giuseppe Larosa Sat, 07/11/2009 - 00:20

Hello Michael,

GRE is another tunneling protocol an alternative to PPTP.

In your flow diagram you say you would like to setup a PPTP tunnel.

There can be combinations of the two protocols.

However, the following document can help

GRE is a protocol over IP (protocol 47)

an acl that permits GRE is written as:

access-list 111 permit gre host x.x.x.x host y.y.y.y

Hope to help



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