If the service provider is having MPLSVPN backbone and would like to serve IPv6 internet; In that case with the help of MP-iBGP this objective can be achieved with no infrastructure changes. This technique is also known as 6PE. Given depicted figure 1 shows the MPLS VPN ip4 cloud with ldp as label distribution protocol and OSPF is implemented as IGP. Edge routers PE1 and PE2 are configured as dual stack router which supports both IPv4 as well as IPv6 addressing. Both edge routers are configured with IPv6 - MP-iBGP with route reflector router. A default IPv6 route is configured on PE2 towards IPv6 Internet Cloud. PE2 is advertising default IPv6 route to RR with label 100 as next hop PE2 ipv4 BGP router id. The same default IPv6 route is installed on PE1 with outgoing IPv6 label 200 with PE2 BGP IPv4 router-id as next hop address.
It shows the pictorial view of forwarding traffic from 6CE to IPv6 Internet cloud. The traffic is first forwarded towards PE 1 which appends the IPv6 label 100 for destination 2001::1::1 and label 20 for the next hop address which is PE2 BGP router id. Then the traffic next moves to IPv4-P1 router which only swaps the topmost 20 label to 21 and forwards towards IPv4-P4/RR router. RR swaps the topmost label 21 to 22 and forwards to the next hop which is IPv4-P2. IPv4 performs the PHP (Penultimate Hop Popping) function and forwards the traffic with IPv6 label towards PE2. PE2 removes the all label and forwards the traffic to IPv6 internet cloud. The main advantage of using MP-iBGP is that the 6CE customers can access the IPv6 internet cloud by using the existing IPv4 cloud. By using LDP IPv6 route becomes hide as in legacy VPNv4, so the core routers doesn’t know about the IPv6 route and only look for the next hop address which is reachable by IGP.
Figure 4 shows the reverse traffic from IPv6 Internet cloud to 6CE.
By using the above mentioned technique, service provider need to use OSPF or IS-IS for IPv6. Also refer to my previous post about the selection of IGP protocol.