Daniel, There were two basic arguments for limiting the length of the TLA prefix: 1) Routing table size. All TLA have to be in all tables in all defaultless routers. Thus, the number of TLAs becomes a minorant of the size of the tables. 2) Address space size. The current document only specifies 1/8th of the address space. If it turns out that there is a need for many more TLA's in three years, it will actually be possible to make some. The particular value chosen, 13 bits, as only one advantage. The combination of format and TLA fits in 16 bits, which provides for easy writing of routing prefixes. The point that you note re: allocation practices is, however, perfectly true. ISPs should not receive a TLA 'a priori", they should graduate to it. If I remeber correctly, an ISP that starts operating in Europe today receives a /19, and will gradually receive more space as it connects more customers. An ISP that starts operating with IPv6 should receive one or several NLAs from established transit providers; it should only receive a global entry in the routing tables once it has passed some "graduation" criteria. -- Christian Huitema