Another try at a proposal for draft-ietf-6man-rfc4291bis-07

David Farmer <> Fri, 03 March 2017 13:54 UTC

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From: David Farmer <>
Date: Fri, 3 Mar 2017 07:54:44 -0600
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Subject: Another try at a proposal for draft-ietf-6man-rfc4291bis-07
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Modified the goals a bit based on feedback;

1. IPv6 unicast routing is 128 bits in length [BCP198], AKA not classful!
2. Subnet Prefixes and IIDs are usually 64 bits
3. IIDs of 64 bit are REQUIRED for SLAAC, except when overridden by an
IPv6-over-foo doc, and we can't change 64 bit IIDs for SLAAC, at least not
now, it would break running code
4. Sites should get more than a /64 [BCP157]
5. Explicitly allow prefix lengths other than 64 bits for manually config
and DHCPv6, most code does this now and has since the beginning
6. Avoid other explicit exceptions or recommendations for longer prefixes,
like RFC6164
7. include references to [BCP204]/[RFC7934] and [RFC6052] in the right

In the current draft remove the 2nd paragraph of 2.4, then add the
following two paragraphs at the end of section 2.4

   IPv6 unicast routing is based on prefixes of any length up to 128
   bits [BCP198]. However, unicast addresses usually have a subnet
   prefix and interface ID of 64 bits in length. The rationale for the
   64 bit boundary in IPv6 addresses can be found in [RFC7421].

   Nevertheless, a unicast address may also be provided from a node's
   internal configuration or via DHCPv6[RFC3515], such addresses are
   assumed to have no internal structure, are treated as a single
   128 bit quantity, and may be associated with a subnet prefix of any

Then replace the 4th paragraph of 2.4.1 with;

   When a unicast address is formed from a subnet prefix and an
   automatically generated interface ID (e.g. Stateless Address
   Autoconfiguration(SLAAC)[RFC4862]), the interface ID is required
   to be 64 bits in length unless overridden in an "IPv6 over
   <link>" specifications. The rationale for the 64 bit boundary in
   IPv6 addresses can be found in [RFC7421].

And replace the second and third paragraphs of 2.4.5 with;

   As noted in Section 2.4, Global Unicast addresses usually have
   a 64-bit interface ID length (i.e., n + m = 64), and are
   formatted as described in Section 2.4.1.

   As discussed in [BCP 157], "it should be easy for an end site to
   obtain address space to number multiple subnets (i.e., a block
   larger than a single /64)" or in other words the subnet ID length
   should be great than or equal to 1 (i.e., m >= 1), with typical
   subnet ID lengths of 4, 8, 12, and 16 bits and therefore typical
   global routing prefix lengths of 60, 56, 52, and 48 bits

A couple other quickies;

Insert new paragraph at the end of 2.1

   [BCP 204] recommends that networks provide general-purpose
   nodes with multiple global IPv6 addresses per interface when
   they attach to a link, describes the benefits of and the options
   for doing so.

Insert new sentence at the end of 2.4.5

   Additional IPv6 address that carry an IPv4 address are defined in
   IPv6 Addressing of IPv4/IPv6 Translators [RFC6052].


David Farmer     
Networking & Telecommunication Services
Office of Information Technology
University of Minnesota
2218 University Ave SE        Phone: 612-626-0815
Minneapolis, MN 55414-3029   Cell: 612-812-9952