# Carrier-of-Carriers IPv6 VPNs Overview

Figure 111 illustrates a carrier-of-carrier scenario with IPv6 VPNs. MPLS labels are exchanged on the PE–CE link for customer-internal routes, but customer-external routes are not imported either into the VRFs on the PE router or into the core. VRFs maintain a routing table only for the customer-internal routes. Forwarding is accomplished primarily by label switching, without a routing table lookup.

Only customer-external routes (Tier 2 ISP routes as shown in Figure 111) can be native IPv6 addresses. Because LDP over TCP over IPv6 is not currently supported, the customer-internal routes for which LDP can give out labels (Tier 1 ISP routes in Figure 111) must be IPv4 addresses; they cannot be IPv6 addresses, whether native or IPv4-mapped.

For more information about carrier-of-carriers VPNs, see Carrier-of-Carriers IPv4 VPNs Overview .

Figure 111: Carrier-of-Carrier IPv6 VPNs