This proposal is essentially what draft-hinden-ipv6-global-site-local-00.txt does. I have no problem with carving off a chunk of FEC0::/10 space for something like this, but that approach does not solve all problems. In particular it creates an unroutable mess for sites with a large number of subnets.
Tony -----Original Message----- From: Christian Huitema [mailto:[EMAIL PROTECTED] Sent: Wednesday, April 02, 2003 12:15 PM To: [EMAIL PROTECTED]; Jeroen Massar; [EMAIL PROTECTED] Cc: [EMAIL PROTECTED] Subject: Globally unique link prefix alternative to site-locals The "anti-SL" arguments are primarily arguments aainst using ambiguous addresses. Ambiguous addresses are a royal pain in hosts that connect to multiple sites, either simultaneously or over time -- the applications need extra logic, and that creates bugs. But we clearly have an issue in the case of disconnected sites, intermittently connected sites, and ad hoc networks. The "let's pick a prefix" argument is probably OK for large "managed" sites. In fact, most of the large sites have at least one IPv4 address and can pick a prefix; they could even obtain a provisional allocation from a friendly ISP. But this leaves out the small sites, the ad hoc networks, the unmanaged sites. However, if we just look at these small sites, we can easily get unambiguous *link* prefixes of the form: <some-16-bit-prefix><unique 48 bit number>::/64 In a small site, these prefixes can be autoconfigured by routers, and then published in the IGP. If there are several routers on the same link, they can either elect a master prefix or just advertise one prefix each. Having unique per-link prefixes has quite a few advantages: - We get actual zero-configuration, a site can be just switched on. - Local connectivity can be used for adding a global addressing plan when the site joins the Internet. - Hosts can be multihomed at will; there is enough information in the address to find the right exit. - The addresses remain valid if a site is split, or if two sites are merged. - Unreachability is enforced by firewalls, not by bits in the address. - Since the link prefix is a /64, there is zero chance of having a nasty ISP leak it to the Internet. - If the /16 is well known, it can be plugged as "least preferred" in the address selection rules. Is anyone interested in pursuing this design? -- Christian Huitema -------------------------------------------------------------------- IETF IPng Working Group Mailing List IPng Home Page: http://playground.sun.com/ipng FTP archive: ftp://playground.sun.com/pub/ipng Direct all administrative requests to [EMAIL PROTECTED] --------------------------------------------------------------------
