RFC 3177 (rfc3177) - Page 2 of 10

IAB/IESG Recommendations on IPv6 Address Allocations to Sites

RFC 3177       IAB/IESG Recommendations on IPv6 Addresses September 2001


2. Background

   The technical principles that apply to address allocation seek to
   balance healthy conservation practices and wisdom with a certain ease
   of access.  On one hand, when managing a potentially limited
   resource, one must conserve wisely to prevent exhaustion within an
   expected lifetime.  On the other hand, the IPv6 address space is in
   no sense as limited a resource as the IPv4 address space, and
   unwarranted conservatism acts as a disincentive in a marketplace
   already dampened by other factors.  So from a market development
   perspective, we would like to see it be very easy for a user or an
   ISP to obtain as many IPv6 addresses as they really need without a
   prospect of immediate renumbering or of scaling inefficiencies.

   The IETF makes no comment on business issues or relationships.
   However, in general, we observe that technical delegation policy can
   have strong business impacts.  A strong requirement of the address
   delegation plan is that it not be predicated on or unduly bias
   business relationships or models.

   The IPv6 address, as currently defined, consists of 64 bits of
   "network number" and 64 bits of "host number".  The technical reasons
   for this are several.  The requirements for IPv6 agreed to in 1993
   included a plan to be able to address approximately 2^40 networks and
   2^50 hosts; the 64/64 split effectively accomplishes this.
   Procedures used in host address assignment, such as the router
   advertisement of a network's prefix to hosts [RFC 2462], which in turn
   place a locally unique number in the host portion, depend on this
   split.  Subnet numbers must be assumed to come from the network part.
   This is not to preclude routing protocols such as IS-IS level 1
   (intra-area) routing, which routes individual host addresses, but
   says that it may not be depended upon in the world outside that zone.
   The 64-bit host field can also be used with EUI-64 for a flat,
   uniquely allocated space, and therefore it may not be globally
   treated as a subnetting resource.  Those concerned with privacy
   issues linked to the presence of a globally unique identifier may
   note that 64 bits makes a large enough field to maintain excellent
   random-number-draw properties for self-configured End System
   Designators.  That alternative construction of this 64-bit host part
   of an IPv6 address is documented in [RFC 3041].

   While the IETF has also gone to a great deal of effort to minimize
   the impacts of network renumbering, renumbering of IPv6 networks is
   neither invisible nor completely painless.  Therefore, renumbering
   should be considered a tolerable event, but to be avoided if
   reasonably feasible.





IAB & IESG                   Informational