over a 3GPP link has turned out to be non-trivial. There are several known and documented shortcomings found in live GPRS networks [166]. These are typically a combination of the end host (the UE) side network interface and link abstraction framework being slightly flawed and the network side PGW being too strict on their interpretation of how IPv6 ought to work on a 3GPP defined link. The outcome is usually that no user plane traffic flows but no one is actually doing anything completely wrong. Next we go through a couple of examples found in live networks. These are documented just for the purpose of learning and possibly to help people to identify possible error cases they face. It is expected (and hoped for) that none of these examples will be found in latest (upgraded) networks and UEs. We want to point out that these error case examples have been checked with multiple UEs vendors and PGWs vendors. End Host Interface Treated as a Router Interface A 3GPP link between a UE and a next-hop router (e.g. the PGW) resembles a point- to-point link, which has no link-layer addresses [157], and this has not changed from 2G/3G GPRS to EPS. The UE IP stack has to take this into consideration. When the 3GPP PDN Connection appears as a PPP interface to the UE, the IP stack is usually prepared to handle the NDP and the related Neighbor Cache state machine transitions in an appropriate way, even though NDP messages contain no link-layer address information. However, some operating systems discard Router Advertisements on their PPP interface as a default setting. This causes SLAAC to fail when the 3GPP PDN Connection gets established, thus stalling all IPv6 traffic. This kind of end host default setting has been there, for example, in Linux and early OS/X operating systems for quite some time. The reasoning has probably been that a PPP link was considered as a router-to-router link, and in that case the interface should not use SLAAC to configure its addresses. IP Stack Incorrectly Requires Address Resolution Currently, seve