For correct work LNS (L2TP Network Server) with LAC (L2TP Access Concentrator) need adding shared-secret for tunnels, and implement command for disabling Compression Control Protocol (CCP). Propose next commands:
# Tunnel password used to authenticate the client (LAC) set vpn l2tp remote-access lns shared-secret 'password' # Disable Compression Control Protocol (CCP) set vpn l2tp remote-access ccp-disable