Brief Description of Error 721:

If you have ever tried to establish a VPN or virtual private network, then you may have come across the Error 721. Error 721, by definition, is a Microsoft Error which occurs when an unsuccessful attempt is made to establish a VPN connection with a corporate network. This connection is established using P2P or Point-to-Point Tunneling Protocol; PPTP client. Another case where users normally encounter Error 721 is when the user make an unsuccessful attempt to establish a dial-up connection; particularly, if the user had recently upgraded his/her operating system to Windows XP. The description of error 721 differs. Two very common descriptions of error 721 are the following:

“Remote Computer is not Responding”

or

“Remote PPP peer is not Responding”

Both messages mean basically the same thing, they are just phrased differently.

What Causes Error 721:

PPTP make use of GRE or the Generic Routing Encapsulation; which is done for tunnelled data. In this scenario, the error usually occurs when the network firewall blocks the GRE or Generic Routing Encapsulation Protocol traffic. Both these protocols i.e., the GRE protocol and the PPTP are used in order to build a VPN or a virtual private network. The virtual private network can be made between the clients only or it can be created between the server and a dedicated client. Another major cause of Error 721 is that the user’s modem might not be compatible with the operating system; Windows XP.

Fixing Error 721:

Error 721 can be resolved with ease. In order to resolve the error 721, all you need to do is to re-configure your settings of the windows network firewall. As it was mentioned earlier that error 721 may result if the network firewall blocks GRE traffic. Therefore, you need to configure the windows network firewall in a way so that the firewall allows the GRE protocol 47. Another step towards resolving or avoid error 721 is that you must check if your firewall allows TCP traffic or not on port 1723; if it doesn’t then you have to configure it so that it allows TCP traffic on port 1723. In order to establish a virtual private network using PPTP, two important conditions are required; the firewall should permit both GRE and TCP traffic.

Another way of fixing the error 721 is to download the latest driver for your modem. Make sure that the latest driver that you download must be compatible with Windows XP; else it won’t do any help in fixing Error 721.

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