# Securing IPv6 Neighbor Discovery Address Resolution with Voucher-Based Addressing
## 2 Background and Motivation
### Related Works  
Well beyond the conception of SEND, researchers continue to strive for an ideal NDP. Research is conducted year after year into denial-of-service protections, protocol extensions, and, most relevant of all, the prevention of spoofing threats. It is important to measure the effectiveness of these endeavors by evaluating how the goal of spoof prevention is achieved while simultaneously preserving the three ideals of privacy preservation, simplicity, and flexibility. These properties are crucial considerations for the widespread success and adoption of any proposed protocol amendment for a technology as widely deployed as Neighbor Discovery. Since this work measures its own efficacy against these same ideals, using this baseline against other relevant research creates an adequate comparison. The Source Address Validation Improvement (SAVI) framework specified in [12] is a proven and effective mitigation for various spoofing strategies. It does so by learning and enforcing known bindings between source IP addresses and source link-layer addresses, along with identifying and associating the switchport used to communicate the messages. However, SAVI has been criticized for both its complex, time-consuming implementation  
Figure 2: A more subversive, “eager” approach to preemptively poisoning a target’s Neighbor Cache without requiring any prior interaction. Each arrow is colored to indicate its associated step in the process; an upward arrow indicates transmission of a message, and a downward arrow indicates receipt of a message. Nodes receiving SLLAO stubs on certain NDP messages are dictated by the protocol specification to accept them as-is for the sake of protocol optimization. This optimization is performed so that NS receivers can respond with unicast messages to the sending link-layer address without needing reverse address resolution and without a multicast response. in large-scale networks and its high false-positive rate of misreported bindings. If deployed across the infrastructure incorrectly, the method SAVI uses to form its associations can lead to horrendous state synchronization problems. Additionally, the framework is often not compatible with multihomed interfaces having multiple IP addresses across many subnets at the same time. As robust as the SAVI solution is, it cannot be considered to satisfy all three ideals because it is neither simplistic nor flexible. [PERSON] et al. introduce the Trust-ND mechanism in [13] as another method specifically designed to abate the neighbor spoofing attack vector by employing a 32-byte NDP Trust Option. This option incorporates a mixture of integrity checking via hashing and a soft-security technique of social trust between independent neighbors. This method was later improved upon by [PERSON] et al. in [14], mitigating weaknesses and granularity issues relating to the Trust Option's Timestamp value. The most interesting aspect of this work is its independence from any centralized infrastructure, opting instead to rely on what neighbors might already know about each other, direct message authentication details, and the calculation of a trustworthiness score, and then making NDP determinations from that information. Decentralization and node-independent trust make Trust-ND very flexible for deployment in mixed networks, where some nodes may not recognize or acknowledge the newly introduced Trust Option. It is also simplistic due to both its introduction of only one new NDP option and a software-based mechanism to accumulate and calculate neighbor trust. However, Trust-ND lacks the preservation of privacy, because the trust score and knowledge of the source node's past activity rely partially on what the receiver (trustor) knows about the sender (trustee), identified by a packet hash and NDP details.