get lost - not necessarily on the actual wireless link segment but between the radio modem and the host IP stack. Therefore, this is a real issue for Split-UEs and specifically on the older UEs that implement dual- stack using two parallel PDN Connections. One typical case is when a dual-stacked network interface gets up on the UE, and a number of eager IPv4 applications immediately send a flood of TCP connection attempts, DNS queries, and various service discovery queries to the modem; this then gets overloaded while the PDN Connection activation is still in progress and as a result the Router Advertisement can just get lost. A decent end host IP stack implementation should send a Router Solicitation after a while but this seems not to be the case in all situations. Solutions to Fix the Situation There are multiple approaches for fixing possible NDP issues regarding the 3GPP link model and IPv6. Some IPv6-enabled radio modems and PGWs are known to do the following hacks/tricks: IPv6 in 3GPP Networks A PGW adds a forged Source Link-Layer Address option into the Router Advertisement message, which makes the UE ND cache transition from the INCOMPLETE state to the STALE state immediately on receiving the Router Advertisement message. A PGW adds a forged Source Link-Layer Address option into the address resolution solicited Neighbor Advertisement message, which makes the address resolution com- plete and the UE ND cache transitions from the INCOMPLETE state to the STALE state immediately on receiving the Neighbor Advertisement message. A radio modem firmware adds a forged Source Link-Layer Address option into the Router Advertisement message on behalf of the PGW. A radio modem firmware unicasts the Neighbor Solicitation to the PGW when a host attempts the address resolution. This looks like an NUD to the PGW, and since all implementations are mandated to respond to the NUD [25], there is a far better chance that the PGW responds with something meaningful in its Neighbor Advertisement (some PGW implementations add a f