1. A method performed in a network node, said method comprising: maintaining a neighbor data structure for storing mapping entries, each mapping entry specifying a local address corresponding to a global address, said neighbor data structure being in the form of a hash table containing a plurality of buckets, said hash table being based on a hash function that generates a corresponding hash value for each global address, wherein each bucket is associated with a unique hash value, wherein each bucket of said plurality of buckets is implemented as a corresponding balanced tree of a plurality of balanced trees, each balanced tree containing a corresponding set of nodes, with each node storing a corresponding mapping entry, wherein, upon applying of said hash function, corresponding global address of mapping entries in each balanced tree generates the unique hash value associated with the bucket; receiving a lookup request containing a first global address; determining a first bucket of said plurality of buckets by applying said hash function to said first global address; and traversing a first balanced tree corresponding to said first bucket to find a first mapping entry having a global address equaling said first global address.