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Versions: 00 01                                                         
v6ops                                                  J. Palet Martinez
Internet-Draft                                          The IPv6 Company
Intended status: Best Current Practice                  October 28, 2017
Expires: May 1, 2018

        Using /64 from Customer Prefix for the Inter-Router Link


   This document describes the usage of a /64 from the customer prefix
   for numbering IPv6 point-to-point links in non-broadcast layer 2

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on May 1, 2018.

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   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Rational for using /64  . . . . . . . . . . . . . . . . . . .   3
   3.  Numbering Interfaces  . . . . . . . . . . . . . . . . . . . .   3
   4.  Routing Aggregation of the Point-to-Point Links . . . . . . .   3
   5.  DHCPv6 Considerations . . . . . . . . . . . . . . . . . . . .   5
   6.  Router Considerations . . . . . . . . . . . . . . . . . . . .   5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   10. Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   There are different alternatives for numbering IPv6 point-to-point
   links, and from an operational perspective, they may have different
   advantages or disadvantages that need to be taken in consideration
   under the scope of each specific network architecture design.

   [RFC6164] describes using /127 prefixes for inter-router point-to-
   point links, using two different address pools, one for numbering the
   point-to-point links and another one for delegating the prefixes at
   the end of the point-to-point link.  However this doesn't exclude
   other choices.

   This document describes an alternative the approach, using a /64 from
   the customer prefix, which ensure compliance with standards, and
   consequently facilitate interoperability, avoids possible future
   issues if more addresses are needed (e.g., managed bridges) and
   simplifies the addressing plan.

   The use of /64 also facilitates an easier way for routing the shorter
   aggregated prefix into the point-to-point link.  Consequently it
   simplifies the "view" of a more unified addressing plan, providing an
   easier path for following up any issue when operating IPv6 networks.

   The proposed approach is suitable for those point-to-point links
   connecting ISP to Customers and enterprise networks, but not limited
   to those cases, and in fact, is being used by a relevant number of
   networks worldwide, in several different scenarios.

   This mechanism would not work in broadcast layer two media that rely
   on ND (as it will try ND for all the addresses within the shorter
   prefix being delegated thru the point-to-point link).

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2.  Rational for using /64

   The IPv6 Addressing Architecture ([RFC4291]) specifies that all the
   Interface Identifiers for all the unicast addresses (except for
   000/3) are required to be 64 bits long and to be constructed in
   Modified EUI-64 format.

   The same document also mandates the usage of the predefined subnet-
   router anycast address, which has cleared to zero all the bits that
   do not form the subnet prefix.

   [RFC6164] describes possible issues when using /64 for the point-to-
   point linkes, however, it also states that they can be mitigated by
   other means, and indeed, considering the publication date of that
   document, those issues should not be any longer considered.  The fact
   is that many operators wordwide, today use /64 without any concerns,
   as vendors have taken the necessary code updates.

   Consequently, we shall conclude that /64 it is a valid approach to
   use /64 prefixes for the point-to-point links.

3.  Numbering Interfaces

   Often, in point-to-point links, hardware tokens are not available, or
   there is the need to keep certain bits (u, g) cleared, so the links
   can be manually numbered sequentially with most of the bits cleared
   to zero.  This numbering makes as well easier to remember the
   interfaces, which typically will become numbered as 1 (with 63
   leading zero bits) for the provider side and 2 (with 63 leading zero
   bits) for the customer side.

   Using interface identifiers as 1 and 2 is not only a very simple
   approach, but also a very common practice.  Other different choices
   can as well be used as required in each case.

   On the other hand, using the EUI-64, makes it more difficult to
   remember and handle the interfaces, but provides an additional degree
   of protection against port (actually address) scanning as described
   at [RFC7707].

4.  Routing Aggregation of the Point-to-Point Links

   Following this approach and assuming that a shorter prefix is
   typically delegated to a customer, for example a /48, it is possible
   to simplify the routing aggregation of the point-to-point links.
   Towards this, the point-to-point link may be numbered using the first
   /64 of the /48 delegated to the customer.

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   Let's see a practical example:

   o  A service provider uses the prefix 2001:db8::/32 and is using
      2001:db8:aaaa::/48 for a given customer.

   o  Instead of allocating the point-to-point link from a different
      addressing pool, it may use 2001:db8:aaaa::/64 (which is the first
      /64 subnet from the 2001:db8:aaaa::/48) to number the link.

   o  This means that, in the case the non-EUI-64 approach is used, the
      point-to-point link may be numbered as 2001:db8:aaaa::1/64 for the
      provider side and 2001:db8:aaaa::2/64 for the customer side.

   o  Note that using the first /64 and interface identifiers 1 and 2 is
      a very common practice.  However other values may be chosen
      according to each case specific needs.

   In this way, as the same address pool is being used for both, the
   prefix and the point-to-point link, one of the advantages of this
   approach is to make very easy the recognition of the point-to-point
   link that belongs to a given customer prefix, or in the other way
   around, the recognition of the prefix that is linked by a given
   point-to-point link.

   For example, making a trace-route to debug any issue to a given
   address in the provider network, will show a straight view, and it
   becomes unnecessary one extra step to check a database that correlate
   an address pool for the point-to-point links and the customer
   prefixes, as all they are the same.

   Moreover, it is possible to use the shorter prefix as the provider
   side numbering for the point-to-point link and keep the /64 for the
   customer side.  In our example, it will become:

   o  Point-to-point link at provider side: 2001:db8:aaaa::1/48

   o  Point-to-point link at customer side: 2001:db8:aaaa::2/64

   This provides one additional advantage as in some platforms the
   configuration may be easier saving one step for the route of the
   delegated prefix (no need for two routes to be configured, one for
   the delegated prefix, one for the point-to-point link).  It is
   possible because the longest-prefix-match rule.

   The behavior of this type of configuration has been successfully
   deployed in different operator and enterprise networks, using
   commonly available implementations with different routing protocols,
   including RIP, BGP, IS-IS, OSPF, along static routing, and no

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   failures or interoperability issues have been reported.

5.  DHCPv6 Considerations

   As stated in [RFC3633], "the requesting router MUST NOT assign any
   delegated prefixes or subnets from the delegated prefix(es) to the
   link through which is received the DHCP message from the delegating
   router", however the approach described in this document is still
   useful in other DHCPv6 scenarios or non-DHCPv6 scenarios.

   Furthermore, [RFC3633] was updated by Prefix Exclude Option for
   DHCPv6-based Prefix Delegation ([RFC6603]), precisely to define a new
   DHCPv6 option, which covers the case described by this document.

   Moreover, [RFC3769] has no explicit requirement that avoids the
   approach described in this document.

6.  Router Considerations

   This approach is being used by operators in both, residential/SOHO
   and enterprise networks, so the routers at the customer end for those
   networks MUST support [RFC6603] if DHCPv6-PD is used.

   In the case of Customer Edge Routers there is a specific requirement
   ([RFC7084]) WPD-8 (Prefix delegation Requirements), marked as SHOULD
   for [RFC6603].  However, in an scenario where the approach described
   in this document is followed, together with DHCPv6-PD, the CE Router
   MUST support [RFC6603].

7.  Security Considerations

   This document does not have any new specific security considerations.

8.  IANA Considerations

   This document does not have any new specific IANA considerations.

9.  Acknowledgements

   The author would like to acknowledge the inputs of Mikael Abrahamsson
   ...  Acknowledgement to co-authors, Cesar Olvera and Miguel Angel
   Diaz, of a previous related document (draft-palet-v6ops-point2point,
   2006), as well as inputs for that version from Alain Durand, Chip
   Popoviciu, Daniel Roesen, Fred Baker, Gert Doering, Olaf Bonness, Ole
   Troan, Pekka Savola and Vincent Jardin, are also granted.

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10.  Normative References

   [RFC3633]  Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
              Host Configuration Protocol (DHCP) version 6", RFC 3633,
              DOI 10.17487/RFC3633, December 2003,

   [RFC3769]  Miyakawa, S. and R. Droms, "Requirements for IPv6 Prefix
              Delegation", RFC 3769, DOI 10.17487/RFC3769, June 2004,

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/info/rfc4291>.

   [RFC6164]  Kohno, M., Nitzan, B., Bush, R., Matsuzaki, Y., Colitti,
              L., and T. Narten, "Using 127-Bit IPv6 Prefixes on Inter-
              Router Links", RFC 6164, DOI 10.17487/RFC6164, April 2011,

   [RFC6603]  Korhonen, J., Ed., Savolainen, T., Krishnan, S., and O.
              Troan, "Prefix Exclude Option for DHCPv6-based Prefix
              Delegation", RFC 6603, DOI 10.17487/RFC6603, May 2012,

   [RFC7084]  Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic
              Requirements for IPv6 Customer Edge Routers", RFC 7084,
              DOI 10.17487/RFC7084, November 2013,

   [RFC7707]  Gont, F. and T. Chown, "Network Reconnaissance in IPv6
              Networks", RFC 7707, DOI 10.17487/RFC7707, March 2016,

Author's Address

   Jordi Palet Martinez
   The IPv6 Company
   Molino de la Navata, 75
   La Navata - Galapagar, Madrid  28420

   Email: jordi.palet@theipv6company.com
   URI:   http://www.theipv6company.com/

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