to search through all entries of the core ipt structure is inefficient, and a hash table may be used to map virtual addresses (and address space/pid information if need be) to an index in the ipt - this is where the collision chain is used. this hash table is known as a "hash anchor table". the hashing function is not generally optimized for coverage - raw speed is more desirable. of course, hash tables experience collisions. due to this chosen hashing function, we may experience a lot of collisions in usage, so for each entry in the table the vpn is provided to check if it is the searched entry or a collision.