1. 1 Pure Dual Stack Implementation IPv4_input/output Module IPv6_input/output Module TCP_UDP_v6_modsTCP_UDP_v4_mods socket_v4_modssocket_v6_mods IPv4 IPv6 ProtocolControlBlockDataStructures ProtocolControlBlockDataStructures Kernel Space User Space socket_apis_v4_AF_INETsocket_apis_v6_AF_INET6 IP Packet Processing IPv4 Applications IPv6 Applications

2. 2 Hybrid Stack Implementation IPv4_input/output Module IPv6_input/output Module TCP_UDP_mods socket_mods IP ProtocolControlBlockDataStructures Kernel Space User Space socket_apis_AF_INET6 OR AF_INET IP Packet Processing IPv4 OR IPv6 Applications

3. 3 Hybrid Stack Core Advantages  Reduces Kernel Bloat and Maintenance  Leaves Socket and Transport Layer in tact with conditionals.  Common Protocol Data Structures for IPv4 and IPv6 using IPv4- Mapped Addresses.  Applications can support both IPv4 and IPv6 using IPv4 Mapped Addresses, so ISVs can ship one binary supporting either IPv4 or IPv6.  Existing IPv4 Binaries keep on running.  Network Layer is a Dual IP Layer leaving below IP specific to data links and data link software.