In the case that a branch office is connected to the headquarters via a VPN connection, the Internet-based VPN connection can be backed up by a direct ISDN dial-in connection. Should the Internet connection fail at either of the two routers, the data transmission is transferred to the ISDN link.
In this scenario we are assuming a fully configured VPN connection between the two networks.
- A LAN-LAN connectivity via ISDN is additionally set up between the two networks. Do not use the Setup Wizard to set up this network connectivity! The Wizard would change the entries in the routing table and would thus upset the function of the VPN network connection. Set up the ISDN network connectivity in both routers manually—with the appropriate entries in the list of remote sites, the PPP list, and with the necessary telephone numbers and access identifiers.
- In the gateway at the headquarters, create an entry in the backup table that acts to backup the VPN remote site via a directly dialed ISDN remote site.
- Further, the router at the headquarters requires an entry for the monitoring of a remote device in the network at the branch office: usually the LAN IP address of the remote VPN gateway. This entry ensures that the router at the headquarters can react immediately to a failure of the VPN connection.
Should there be a failure in the connection between the headquarters and branch office (on the way to the Internet provider or at the provider itself) then the ISDN connection takes over the data transfer independent of the Internet.
