ipv6 and l2tp tunnels — Truman Boyes

Recently I was asked about wholesaling scenarios or cases where there is L2TP LACs that the service provider runs and individual ISPs that run LNS in a broadband environment. When IPv6 is being used, it is possible to use ipv4 L2TP tunnels between the LAC and LNS, which will carry the IPv6CP (NCP) which in turn will address the IPv6 host/network at the customer’s residential gateway.

As per RFC 4779:

6.2.3.1.  IPv6 Related Infrastructure Changes

   In this scenario, the BRAS is forwarding the PPP sessions initiated
   by the subscriber over the L2TPv2 tunnel established to the L2TP
   Network Server (LNS), the aggregation point in the ISP network.  The
   L2TPv2 tunnel between the L2TP Access Concentrator (LAC) and LNS can
   run over IPv6 or IPv4.  These capabilities have to be supported on
   the BRAS.  The following devices have to be upgraded to dual stack:
   Host, Customer Router, and Edge Router.  If the tunnel is set up over
   IPv6, then the BRAS must be upgraded to dual stack.

Originally published on truman.net. See the archived copy.