In this mode, L2TP provides the transport for IPv4 that allows full ESM capabilities on the 7750 SR. From the node’s perspective, the L2TP tunnel is no different in capability to those already supported. Only the underlying transport (IPv6 instead of IPv4) distinguishes this approach.
To support legacy IPv4 access, L2TP over IPv6 is combined with the existing L2-Aware NAT feature as shown in Figure: L2TP over IPv6.
As ESM is used, scale is limited by the number of ESM hosts supported on a chassis and any associated resources like queues.
L2TP LNS over IPv6 is supported in both the base routing instance and VPRN that has 6VPE configured.
Like the LNS implementation, tunnels are terminated on any routing interface, including loopback, SAP, or network port. A single interface simultaneously supports IPv4 and IPv6 L2TP tunnel termination by having two different addresses configured.
For greater scalability, L2TP tunnel and session count per chassis are increased to allow 1 tunnel per session.
NAT capabilities are supported by existing L2-Aware NAT methods. Note that the L2TP LNS over IPv6 may be used without NAT as well and the L2TP sessions may be either IPv6-only or dual-stack.