 cellular operator point of view. We have experimented with RFC 4191 and IPv6 offloading in live networks with multiple-interface UEs. Since modifying a live network PGW is typically not an option for experimentation, it is simpler to extend an external router such as L2TP Network Server (LNS) in Layer 2 Tunneling Protocol (L2TP) based external Access Point Name (APN) router deployments (see Section 4.2.4). The required Router Advertisement injecting tools can be implemented in the APN termination router. When the APN is terminated to an external router, the PGW essentially becomes a bridge and the APN terminating router is the first-hop router for UEs. The setup that the authors used for the proof of concept allowed sending of Router Advertisements with RFC 4191 support, among various other Neighbor Discovery messages, from the network to a specific UE. Host OSs typically prefer WLANs over cellular access. For example, Linux implicitly prefers WLAN access over cellular access, thus prioritizing the first-hop router(s) on WLAN access over the first-hop router on a cellular access. For consistency, we should Deploying IPv6 in 3GPP Networks always use LOW default router priority on the cellular access. Since the default router priority on other interfaces is implicitly MEDIUM, the host IP stack will prefer any other interface for default destinations than cellular. When the cellular operator wants to route certain traffic over the cellular, it only needs to send a Router Advertisement with an RIO containing the IPv6 prefix(es) for those destinations (e.g., prefix(es) used to number the operator's own services). The default router and default address selection algorithm [10] in the host IP stack will take care of selecting an appropriate interface for the new IPv6 connections (e.g., existing TCP connections will not move). When the model of operation is 'offload everything except specific destinations', the number of routing rules can be kept low. If the UE has multiple PDN Connections, the PGW on each of those cell