Enter l2tpns

A post from Adrian Kennard on the l2tpd-devel mailing list sounded promising:  his user-space “L2TP NS” solution using the Ethertap device seemed capable of scaling to the level required.

The idea was simple and elegant—the majority of packets in an L2TP session are IP data to/from the customer, and are handled trivially in user-space:  hack the L2TP and PPP headers off packets from the LAC and push the remainder (an IP frame) out to the world; tack headers onto incoming IP packets and send back to the LAC.

Adrian was kind enough to place the code under the GPL and send us a copy.