Pekka, My comments are inline.
Best Regards, Jeffrey Dunn Info Systems Eng., Lead MITRE Corporation. (301) 448-6965 (mobile) -----Original Message----- From: Pekka Savola [mailto:[EMAIL PROTECTED] Sent: Thursday, October 02, 2008 3:48 AM To: Dunn, Jeffrey H. Cc: Brian Dickson; Brian E Carpenter; Alexandru Petrescu; IETF IPv6 Mailing List; Ron Bonica; [EMAIL PROTECTED]; Pasi Eronen; Sherman, Kurt T.; [EMAIL PROTECTED]; [EMAIL PROTECTED]; [EMAIL PROTECTED]; [EMAIL PROTECTED]; V6ops Chairs; Martin, Cynthia E. Subject: RE: what problem is solved by proscribing non-64 bit prefixes? >>On Wed, 1 Oct 2008, Dunn, Jeffrey H. wrote: >> 1. It seems rather wasteful to assign 2^64 addresses to each link. >> This assignment corresponds to. 1.8x10^19 individual end systems. Even >> if this number of systems could be attached to a link, each speaker >> would only be able to transmit an octet every 4679 YEARS to the router v> on a gigabit link. I see no possible application for such an >> arrangement. >The point is not to able able to put 2^64 hosts on a link, it's being >able to put *enough* nodes on the link, with *near-zero* address >collision probability, so that you'll never need to renumber the link >to have more address space if the address space was not sufficient >after the number of connected hosts grow. An added bonus is an >ability to design new protocols and mechanisms that are able to >leverage those bits in the address with reasonable expectation of said >technology being usable in the wild. While I agree with your assertions concerning flexibility and robustness, I do not agree that 2^64 is the minimum number of nodes that should be supported on a link. Consider current IPv4 deployments. I doubt anyone have configured a single router interface with any prefix shorter than /8 (24 bits for hosts). As a result, it would seem to me to be a reasonable and conservative to assume that one might want to use an IPv6 /96 (32 bits for hosts). Regardless of that, I see no reason to constraint folks from using other numbers of bits, both more and less than 64. The bottom line is that I do not understand why folks feel the need to constrain network architects and administrators to use only 64 bit prefixes. >> 2. Since each VLAN is a link, i.e., a separate Ethernet broadcast >> domain, each VLAN on a physical interface must have its own prefix. As >> a result, to support the use of all possible VLAN identifiers (2^12 >> possibilities) each router interface with a VLAN module must be >> assigned at least a /52. For routers with multiple VLAN modules, 16 >> for example, this corresponds to the individual router requiring a /48. >> Although this is a worst case scenario, it illustrates the possibility >> of an enormous waste of address space. >You're not reserving a block of 2^12 IPv4 prefixes (or addresses in >degenerate case) for each VLAN-capable router interface today, so I >fail to see how this argument would apply to IPv6. That is because you did not read the initial paragraph, which points out that SLAAC requires a one-to-one mapping of prefixes to links, e.g., Ethernet broadcast domains. In addition, OSPFv3 also forbids prefixes from spanning interfaces. As a result, 2^13 prefixes could be required if one wanted to be sure that all 2^13 VLAN identifiers were available to a given physical interface. This fits in with your statement about the ability to design new protocols and mechanisms to leverage address bits. -- Pekka Savola "You each name yourselves king, yet the Netcore Oy kingdom bleeds." Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings -------------------------------------------------------------------- IETF IPv6 working group mailing list [email protected] Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
