The solution that was finally implemented in SEEREN infrastructure combined 6PE services at the NREN CE routers with transparent forwarding of IPv6 traffic over the Carrier Provider MPLS network. This solution did not require any software or hardware upgrades in the Carrier Provider network nor the creation of tunnels between the CE routers.

The 6PE deployment approach allows an ISP to support IPv6 services over an MPLS/IPv4 network. It has many technical implementation similarities to the MPLS VPN deployment solutions, where IP traffic is encapsulated into MPLS frames and sent over the MPLS core network.

At the SEEREN infrastructure, the NREN border routers act as 6PE routers and encapsulate IPv6 packets into MPLS frames. Concurrently, the NREN border routers act as CsC-CE routers and thus also encapsulate IPv4 (or IPv6) packets into MPLS frames. Consequently, the control and data plane of the CsC/6PE approach differs from the respective planes of either 6PE or CsC approaches.

In the CsC/6PE control plane, the 6PE routers (the NREN border routers) are dual stack, i.e. support IPv6 and IPv4 protocols, and communicate with the rest local NREN infrastructure with any common IPv6-enable routing protocol. The routing prefixes learned from the local networks are distributed among the 6PEs via multi-protocol MBGP (MP-iBGP). The BGP next-hop for each advertised IPv6 prefix derives from the IPv4 address of the connected 6PEs. Furthermore, the 6PE routers, now acting as CE routers in the CsC context, exchange routing and label information with the Service Provider (IPv4-only) PE routers. This process allows the 6PE routers to identify the labels for the IPv4 next-hop address for all destinations in the VPN, i.e. IPv4 addresses of CsC-CE routers. Finally, communication among CsC-PE routers is achieved via “pure” MPLS switching, where the (IPv4) IGP protocol is used for the distribution of appropriate MPLS labels for CsC-PE addresses.

In the data plane, IPv6 packets are sent from the local infrastructure routers to the NREN ingress 6PEs router. The latter imposes two labels on top of the IPv6 packet. The inner label identifies the IPv6 BGP next-hop and the outer label identifies the egress 6PE router. After the MPLS frame is received by the ingress CsC-PE router, the latter will replace the outer label in order to identify the VPN that the encapsulated packet belongs to. On top of the two labels, the ingress CsC – PE router will stack one additional label that identifies the MPLS-next hop along the path to the egress CsC – PE router. This label changes as the MPLS frame is switched inside the Service Provider MPLS core network. If MPLS penultimate hop poping operation is activated, the egress CsC-PE router receives an MPLS frame with two labels and removes the outer label as it forwards the frame to the 6PE router. Finally, the egress 6PE router removes the remaining label and forwards the IPv6 packet to the appropriate CE.