ALTERNATIVE PATH

System administrators often want a network connection system that switches transparently to a backup if the primary connection goes down. But if you use a VPN with IPsec to protect your traffic en route through the Internet, the backup line needs some special attention. The reason for this attention is that IPsec [1] [2] requires consistent IP addresses at the endpoints of a tunnel, so when the network switches to a different tunnel, the IP addresses must switch to the new endpoints or else existing connections will be terminated. The Border Gateway Protocol (BGP [3]) offers a reliable means of maintaining a highly-available pool of IP addresses with a number of providers. Unfortunately, provider service agreements often prevent admins from using BGP for an existing Internet connection.