Mike, Actually, you cannot just assign a /48 to each site. The RIR H-ratio requirements may make this infeasible. Further, each /48 (/56 for IANA) allocations must be registered with the RIR, which is an administrate headache. Finally, there is the issue of reverse lookup registration for sites. These are just the policy issues.
I think what Brian was trying to point up is that mapping the IPv6 sub-netting scheme to an existing IPv4 sub-netting scheme would be easier of the number of low order bits below the prefix in an address is the same. For example, a IPv4 /24 with 8 low order bits below the prefix might be mapped to a /120 IPv6 address. Clearly, this could be abstracted to a scheme using 2 or 4 x (32 - IPv4 prefix length) low order bits in the IPv6 address, i.e., assign a /n, where n = 128 - 2 or 4 x (32 - IPv4 prefix length). Best Regards, Jeffrey Dunn Info Systems Eng., Lead MITRE Corporation. (301) 448-6965 (mobile) -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Sent: Tuesday, September 30, 2008 12:25 PM To: [EMAIL PROTECTED]; Dunn, Jeffrey H. Cc: [EMAIL PROTECTED]; [email protected]; [EMAIL PROTECTED]; [EMAIL PROTECTED]; [EMAIL PROTECTED]; Sherman, Kurt T.; [EMAIL PROTECTED]; [EMAIL PROTECTED]; [EMAIL PROTECTED]; [EMAIL PROTECTED]; [EMAIL PROTECTED]; Martin, Cynthia E. Subject: RE: what problem is solved by proscribing non-64 bit prefixes? > When managing such a scheme alongside an IPv6 prefix which > needs to be assigned to the same set of servers, which are > all dual-stack, the *number* of prefixes, their *relative* > numbering, and the host *addresses* within the prefixes, it > is quickly apparent that use of only /64 prefixes makes for a > management nightmare, particularly if renumbering of prefixes > and/or servers occurs, e.g. re-balancing the VLSM arrangement > itself in IPv4-land. Given that in IPv6, you can justify allocating a /48 to each separate site, which gives you 16 bits to mirror the IPv4 subnet hierarchy, while maintaining 64 bit interface sddresses, I don't see a technical issue here. And I would really recommend that you upgrade all of your management systems to fully support IPv6 instead of relying on tricks like generating an IPv6 address by applying a transform to an existing IPv4 address. Then you have no technical issue at all. --Michael Dillon -------------------------------------------------------------------- IETF IPv6 working group mailing list [email protected] Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
