Routing algorithms choose a next hop according to an estimate of distance in some addressing
space. Pastry and Tapestry both use circular linear address spaces in which a function based on the
approximate numerical difference between GUIDs determines their separation. Kademlia uses
the XOR of the GUIDs. How does this help in the maintenance of routing tables? Does the XOR
operation provide appropriate properties for a distance metric?

What will be an ideal response?

The Kademlia paper states that the symmetry of the XOR operation ensures a simple and efficient routing
mechanism. It results in symmetric routing tables being which isn’t true for some other routing algorithms. (It
is for Pastry, but not for Chord). Symmetry means that nodes can learn new routing information from incoming
messages, since the routes they have taken are reversible. In Kademlia the XOR of the GUIDs for the source
and destination nodes is treated as a numeric distance metric and this results in a sensibly-behaved distance
metric (see Kademlia paper Section 2.1).