The Cisco 6PE solution enables IPv6 domains to communicate with each other over an MPLS IPv4 core network. MP-BGP in the IPv4 network is used to exchange IPv6 reachability information along with a label for each IPv6 prefix announced. 6PE routers are dual-stack routers i.e. running IPv6 with the customers and IPv4 in the core.
6PE routers do the following:
Participate in V4 IGP to establish internal reachability inside the MPLS cloud
Participate in LDP for binding V4 labels
Run MP-BGP4 (Multi-Protocol iBGP) to advertise v6 reachability and distribute V6 labels among them
The labels can be distributed as follows:
Per-Prefix label - The 6PE node distributes labels for each IPv6 prefix learnt from interfaces connected to CE routers
Run IPv6 routing protocols (eBGP6, Static, ISIS v6, OSPF v3 , EIGRP v6, iBGP) with CE routers to advertise V6 reachability learnt from their peers over the MPLS cloud
IGP protocol between CE to PE has to be redistributed into MP-iBGP for end to end reachability
6PE with iBGP between CE and PE
6PE with iBGP between PE and CE is supported since IOS-XR 4.0. Unlike IOS an important mandatory configuration command is required in IOS-XR. It is required to configure "ibgp policy out enforce-modifications" under router bgp <AS> to allow changing attributes on the RR for reflected routes.