5.1. From the Standpoint of the Internet

5.1. From the Standpoint of the Internet

There is a mismatch between the structure of IPv6 local addresses and the normal IPv6 wide area routing model. The /48 prefix of an IPv6 local addresses fits nowhere in the normal hierarchy of IPv6 unicast addresses. Normal IPv6 unicast addresses can be routed hierarchically down to physical subnet (link) level and only have to be flat-routed on the physical subnet. IPv6 local addresses would have to be flat-routed even over the wide area Internet.

Thus, packets whose destination address is an IPv6 local address could be routed over the wide area only if the corresponding /48 prefix were carried by the wide area routing protocol in use, such as BGP. This contravenes the operational assumption that long prefixes will be aggregated into many fewer short prefixes, to limit the table size and convergence time of the routing protocol. If a network uses both normal IPv6 addresses [ADDARCH] and IPv6 local addresses, these types of addresses will certainly not aggregate with each other, since they differ from the most significant bit onwards. Neither will IPv6 local addresses aggregate with each other, due to their random bit patterns. This means that there would be a very significant operational penalty for attempting to use IPv6 local address prefixes generically with currently known wide area routing technology.