5.1 INTRODUCTION

Neighbor Discovery (ND) protocol defined in RFC 2461 offers a number of advantages to IPv6. ^[1] This protocol integrates several services which are already used in IPv4, such as Address Resolution Protocol (ARP), Reverse Address Resolution Protocol (RARP), router discovery, and redirect service. It also has newly added functions such as parameter discovery, address autoconfiguration, next-hop determination, neighbor unreachability detection, and duplication address detection, which are not covered in IPv4. In Table 5-1, services provided by ND protocol are specified in detail. We explain only four services provided by ND in this chapter: address resolution, neighbor unreachability detection, router and prefix discovery, and redirect. Duplication address detection will be discussed in the following chapter. New services may be added in ND in the near future.

• Address resolution is the process by which a node determines link-layer address from a given IP address. Sending nodes should perform address resolution to send unicast packets if they do not have knowledge about the link-layer address corresponding to the unicast address.

• Neighbor Unreachability Detection (NUD) enables a node to confirm that packets sent to the neighbor will be correctly forwarded to the destination. NUD may provide significant improvements in robustness of the packet delivery process. It is especially useful for unreliable networks because a part of the routing path in the network can be failed.

• Duplication Address Detection (DAD) ^{[2] [3] [4]} allows a node to find out whether the specific address it try to use is already allocated to...