Все верно почитай про L2TPv3
Вот эта фича должна поддерживаться и софтом и железом:
http://tools.cisco.com/ITDIT/CFN/Dispatch?act=featdesc&task=display&featureId=1604
L2TPv3 - Layer-2 Tunneling Protocol Version 3
This is the next major revision to L2TP.
L2TPv3 combines an enhanced L2TPv2 control plane with an optimized 2 field header.
L2TPv3 is designed to enable customers with a native IP-based infrastructure to allow for transparent LAN services.
L2TPv3 includes support for multiple Layer 2 encapsulations, including 802.1Q virtual LAN (VLAN),
Cisco High-Level Data Link Control (HDLC), Ethernet, Frame Relay, Packet over SONET (POS),
and Point-to-Point Protocol (PPP) support. The enhancements allow customers to essentially connect two similar
interfaces back-to-back without any knowledge of the underlying IP network used to deliver their frames.
Почитай:
Feature Guide http://www.cisco.com/univercd/cc/td/doc/product/software/ios123/123newft/123t/123t_2/gtl2tpv3.htm
FM in 12.0(23)S http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/120newft/120limit/120s/120s23/l2tpv323.htm