Mark Lewis, CCIE (R) No. 6280, is technical director of MJL Network Solutions (www.mjlnet.com), a leading provider of internetworking solutions that focuses on helping enterprise and service provider customers to implement leading-edge technologies. Mark specializes in next-generation network technologies and has extensive experience designing, deploying, and migrating large-scale IP/MPLS networks. He is an active participant in the IETF, a member of the IEEE, and a certified Cisco Systems (R) instructor. Mark is the author of Troubleshooting Virtual Private Networks, published by Cisco Press.