Again, with MP-BGP, the transport is independent of the NLRI, or payload, of the BGP peering session. So in the following example, you have two routers with an existing IPv4 peering session transporting both IPv4 and IPv6 advertisements.
Note the activation of the IPv4 neighbor within the IPv6 address-family configuration. An IPv6 neighbor must be activated within the address family to transport NLRI.
In addition to IPv4 and IPv6 address-families, there are also VPNv4 and VPNv6 address-family types for MPLS purposes. Note that if the unicast keyword is not specified in the address-family command for IPv6, it will configure as unicast by default.
There is no mask keyword when defining the network command for IPv6 addresses. There are, however, arguments for ipv6-prefix and ipv6-length to specify addressing and prefix length, respectively.
Stuck-in-Active: Journal of an IT-Network Administrator 