6PE Configuration
This chapter explains about IPv6 islands over IPv4 MPLS using IPv6 Provider Edge Routers (6PE). With this technique, IPv6 islands are connected to each other across an IPv4 backbone enabled with MPLS label stacking while MP-BGP is used to announce the IPv6 routes across these MPLS tunnels. This feature can be implemented with label- switched paths (LSPs) using the Label Distribution Protocol (LDP) or Resource Reservation Protocol (RSVP).
This feature offers the following options to the service providers:
| • | Connect to other IPv6 networks accessible across the MPLS core. |
| • | Provide access to IPv6 services and resources that the service provider provides. |
| • | Provide IPv6 VPN services without going for the complete overhaul of the existing MPLS/IPv4 core. |
The 6PE uses the existing IPv4 MPLS core infrastructure for IPv6 transport. It enables IPv6 sites to communicate with each other over an IPv4 MPLS core network using MPLS label switched paths (LSPs). This feature relies heavily on multiprotocol Border Gateway Protocol (BGP) extensions in the IPv4 network configuration on the provider edge (PE) router to exchange IPv6 reachability information (in addition to an MPLS label) for each IPv6 address prefix. Edge routers are configured as dual-stack, running both IPv4 and IPv6, and use the IPv4 mapped IPv6 address for IPv6 prefix reachability exchange.
Benefits of 6PE
6PE offers the following benefits to service providers:
| • | Minimal operational cost and risk - No impact on existing IPv4 and MPLS services. |
| • | Only provider edge routers require upgrade - A 6PE router can be an existing PE router or a new one dedicated to IPv6 traffic. |
| • | No impact on IPv6 customer edge (CE) routers - The ISP can connect to any CE router running Static, IGP or EGP. |
| • | Production services ready - An ISP can delegate IPv6 prefixes. |
| • | IPv6 introduction into an existing MPLS service - 6PE routers can be added at any time. |
IPv6 on Provider Edge Routers
The 6PE is a technique that provides global IPv6 reachability over IPv4 MPLS. It allows one shared routing table for all other devices. 6PE allows IPv6 domains to communicate with one another over the IPv4 without an explicit tunnel setup, requiring only one IPv4 address per IPv6 domain. While implementing 6PE, the provider edge routers are upgraded to support 6PE, while the rest of the core network is not touched (IPv6 unaware).
This implementation requires no re-configuration of core routers because forwarding is based on labels rather than on the IP header itself. This provides a cost-effective strategy for deploying IPv6.The IPv6 reachability information is exchanged by PE routers using multi-protocol Border Gateway Protocol (mp-iBGP) extensions. 6PE relies on mp-iBGP extensions in the IPv4 network configuration on the PE router to exchange IPv6 reachability information in addition to an MPLS label for each IPv6 address prefix to be advertised. PE routers are configured as dual stacks, running both IPv4 and IPv6, and use the IPv4 mapped IPv6 address for IPv6 prefix reachability exchange. The next hop advertised by the PE router for 6PE prefixes is still the IPv4 address that is used for IPv4 L3 VPN routes.
The following figure illustrates the 6PE topology.