ghbor Discovery Proxying (see Section 3.4.10) are available for hosts. A special case of the above, and a requirement for network link numbering, has appeared for inter-router point-to-point links and is described in RFC 6164 [118]. If a 64-bit global prefix is used in a point-to-point link not using link-layer addresses, a ping-pong attack could be launched by sending a packet that would keep bouncing between routers. For link-layers using links-layer addresses resource consumption attack is possible by forcing routers to create Neighbor Cache entries to INCOMPLETE (see Section 3.4.4) state. An additional yet small benefit of /127-prefix usage is an IPv6 address space conservation. The Neighbor Cache resource consumption attack vector can impact hosts as well, especially those that are performing tethering functions. These hosts need to implement some means for mitigating these resource-consuming attacks, such as by rate limiting ICMPv6 messages and cleaning caches from INCOMPLETE entries [72]. Numbering of Star Topology On some occasions, designers build networks that have a single link layer implemented on top of a star topology consisting of point-to-point links from a central point towards end nodes. As the network is considered - from an IPv6 perspective - to be a single link, it also has a shared prefix for all nodes on the branches. In such a deployment all Neighbor Discovery messages, such as those for DAD, have to be bridged via a central point and multiplied to all branches. Simple bridging of all multicast traffic to all branches may consume resource unnecessarily, and hence solutions such as switching may be used. An efficient switching requires the central point to keep perfect awareness of addresses in use in the various branches, and that increases the required state and risks of failures. Therefore, the best known practice to number a star topology is to allocate a unique prefix for each branch of the topology, as is done in 3GPP networks. Deploying IPv6 in 3GPP Networks 3.6.4 Bridging of Link Ty