Randy; > are you asking if the forwarding look-up is longest match on 64 or 128 bits? > i think the latter is mandatory. we do allow allocation of /128s. Can't backbone routers assume 48 bit look-up for best effort unicast forwarding? Though who want to sell value-added (such as MPLS) routers may disagree, it is important for low-cost high-speed Internet. Masataka Ohta