When the IPv6 islands are separated by multiple IPv4 domains, the autonomous system boundary routers between the IPv4 domains must be DS-BGP routers (Figure 111).
Figure 111: IPv6 Tunneled Across IPv4 Domains
Each of these AS boundary routers establishes a peer relationship with the DS-BGP routers in its own domain, creating a separate mesh of tunnels among the DS-BGP routers of each domain. Routing between PE 1–ASBR 1 in AS 1 and between PE 2–ASBR 2 in AS 2 is accomplished by means of label-switched paths.
IPv6 unlabeled routes are exchanged through the external MP-BGP session between ASBR 1 and ASBR 2. Interdomain MPLS tunnels spanning multiple ASs are not supported.
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