Additional 3GPP Deployment Options Section 4.2.4 discussed external PDN access that was realized using a L2TP tunnel between the PGW in the role of L2TP Access Concentrator (LAC) and a LNS in an exter- nal PDN. The same approach could be used for Homenet purposes today. Figure 6.4 shows a deployment option using L2TP for the PGW and the external network connectivity. Deploying IPv6 in 3GPP Networks /64 IPv6 DHCP(v6) servers ((9)) Homenet, IP-only L2TP tunnel over S(G)i Internet or dual-stack Delegating router, DHCP(v6) Operator core / PDN server/relay Other IPv6 prefix using DPCPv6-PD or just routed Figure 6.4 Homenet deployment option using L2TP. There would not necessarily be a need for a DHCPv6 Prefix Delegation for delivering the subscriber prefix to the CPE. The IPv6 prefix assigned to the subscriber would be 'statically' routed to the residential home network, when the PDN Connection from the CPE to the PGW is up. Alternatively, the LNS can have a role of a DHCPv6 server or a relay, and let the CPE in the residential network request delegated prefixes using DHCPv6 Prefix Delegation. There is no similar aggregation requirement for the IPv6 prefix assigned to the PDN Connection and the assigned residential home network IPv6 prefix than there is for 3GPP Release-10 defined DHCPv6 Prefix Delegation. Such 'mis- alignment' of the requirements originates from the fact that the L2TP-based solution is not a 3GPP standard but just a common vendor supported feature. On the other hand, the described L2TP-based deployment would then lose possible PCC integration benefits, since PCC cannot handle non-aggregated prefixes. Actually, it would also be possible for the residential home network CPE to speak one of the common interior routing protocols towards the LNS, and in that way get the routing in place between the home network and the mobile operator PDN. Port Control Protocol Hosts in the Internet very commonly run applications that utilize long-lived connections or need to be able to receive incoming connections. Typic