As the IPv6 Internet grows, alias resolution in IPv6 becomes more important. Traditional IPv4 alias resolution techniques such as Ally do not work for IPv6 because of protocol differences. Recent techniques adopted specifically for IPv6 have shown promise, but utilize source routing, which has since been deprecated, or rely upon sequential fragment identifiers supported on only a third of router interfaces. As a result, IPv6 alias resolution remains an open problem. This paper introduces UAv6, a new alias resolution technique for IPv6. UAv6 finds aliases in two phases. The first "harvest" phase gathers potential alias pairs, and is based on our empirical observation that addresses adjacent to router interface addresses are often unused. UAv6 probes these unused addresses, eliciting ICMPv6 Address Unreachable responses. The central assumption of this work is that the source address of such a response belongs to a router directly connected to the prefix containing the unused and router interface addresses. The second "disambiguation" phase determines which interface address is an alias of the Address Unreachable's source address. UAv6 uses both new and established techniques to construct proofs or disproofs that two addresses are aliases. We confirm the accuracy of UAv6 by running the Too-Big Trick test upon the aliases we find, and by comparing them with limited ground truth. We also show that the classic address-based technique to resolve aliases in IPv4 works for IPv6 as well, and show that the address-based technique, UAv6, and the Too-Big Trick are complementary techniques in resolving IPv6 aliases.
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