Upgrading and Repairing Networks (5th Edition)

Although IPv6 contains a field that defines the maximum number of hops (the Hop-to-Hop field), it is not required that all nodes support this function, though they can if desired. Instead, upper-layer protocols (such as TCP) are generally delegated this responsibility.

In addition, upper-level protocols should be aware that the maximum payload space has been reduced if IPv6 headers are to be added to the packet. Again, this is a modification that will require that upper-layer protocols be modified, or that the source use fragmentation to deliver packets to their destination.