Internet DRAFT - draft-francis-ipngwg-site-def


Internet Draft                                                P. Francis
<draft-francis-ipngwg-site-def-00.txt>                    TAHOE Networks
                                                             Apr. 1,2001
                          IPv6 Site Definition 
Status of this Memo  
   This document is an Internet-Draft and is in full conformance with 
   all provisions of Section 10 of RFC2026.  
   Internet-Drafts are working documents of the Internet Engineering 
   Task Force (IETF), its areas, and its working groups.  Note that 
   other groups may also distribute working documents as Internet-
   Internet-Drafts are draft documents valid for a maximum of six 
   months and may be updated, replaced, or obsoleted by other documents 
   at any time.  It is inappropriate to use Internet-Drafts as 
   reference material or to cite them other than as "work in progress."  
   The list of current Internet-Drafts can be accessed at  
   The list of Internet-Draft Shadow Directories can be accessed at 
1  Introduction 
   A key concept in IPv6 is that of the site.  Unfortunately, there is 
   no rigorous definition of a site.  Rather, a site is only loosely 
   and informally defined as "a region of topology that belongs to a 
   single organization and is located within a single geographic 
   location" [1]. 
   This document rectifies this situation.  It gives a rigorous 
   definition of site, based on the basic loose definition so far 
   provided.  One of the primary advantages of the definition chosen is 
   that it allows routers to autoconfigure site boundaries. 
1.1 Conventions used in this document 
   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 
   this document are to be interpreted as described in RFC 2119 [2]. 
2  Problem 
   The definition of a site is currently too loose.  The phrase "single 
   geographic location" is too ambiguous.  Network managers may not 
Francis                 Expires Sept. 1, 2001                   Page 1
                         IPv6 Site Definition             Apr. 1, 2001 
   know if a given network topology constitutes a single site or 
   multiple sites. 
   For instance, there can be little disagreement that the following 
   network topology is a single site: 
      R     R                        R      R 
      |     |                        |      | 
     ---------                      ---------- 
         |                              | 
     East Wing                      West Wing 
   In this topology, separate networks in the east and west wings of a 
   single building are connected by a point-to-point link (only 
   routers, not hosts, are shown).  A router in the west wing is 
   attached to an ISP. 
   The following network topology, on the other hand, is clearly not a 
   single site: 
      R     R                        R      R 
      |     |                        |      | 
     ---------                      ---------- 
         |                              | 
     LA Branch                       NY Branch 
   Here, the separate networks are on opposite U.S. coasts, clearly too 
   far apart to be a single site. 
   It is not clear, however, whether the following topology is a single 
   site or two sites: 
      R     R                        R      R 
      |     |                        |      | 
     ---------                      ---------- 
         |                              | 
     Left Bank                      Right Bank 
Francis                 Expires Sept. 1, 2001                   Page 2
                         IPv6 Site Definition             Apr. 1, 2001 
   In this network, the two halves are close together, but not that 
   close together. 
   It is critical that site administrators be able to determine what is 
   and isn't a site. 
3  Site Definition 
   The only way to unambiguously define site and still stay in the 
   spirit of the current understood definition is to nail down the 
   geographical boundaries of a site.  There are a number of ways to do 
   this.  One could, for instance, specify only the area that a site 
   may cover, for instance one square kilometer, but not specify the 
   shape of the site.  If the site covered a multi-story building, then 
   each story could contribute to the square footage.   
   The problem with this approach is that it does not lend itself to 
   easy autoconfiguration of site boundaries.  This is because the 
   shape of the site is left unspecified.  Autoconfiguration is one of 
   the key benefits of IPv6, so an approach that supports 
   autoconfiguration of site boundaries is preferable. 
   This draft proposes the following rigorous definition of a site:  
   A site is defined as the set of routers that fit inside a hexagonal 
   shape with a distance of one kilometer between opposite corners.  
   Any hosts sharing a link with a router in a given site are 
   considered part of the site.  The hexagonal shape is chosen because 
   it can be tiled while still approximating a circle. 
   The administrator is free to decide exactly where to lay the 
   hexagons.  However, they MUST not overlap, and every router MUST be 
   within the boundary of one and only one hexagon.  All stories of a 
   multi-story building are considered to be in the site covered by the 
   Since a site must be internally connected (that is, a path from any 
   router in the site must only go through routers in the site), a 
   given tiling may cause some sites to be partitioned.  In these 
   cases, either a different tiling must be chosen, or additional links 
   must be added to connect the site internally. 
4  Site Boundary Autoconfiguration 
   A site can be completely defined with three parameters:  the 
   longitude and latitude of the center of the site, and the number of 
   degrees west of north of a corner.  We call this the site bearing. 
   Given these three parameters, any router can decide if it is a given 
   site or not.  To autoconfigure a site, one router in the site MUST 
   be configured with the site bearing.  In addition, every router MUST 
   be configured with its own longitude and latitude (position).  
Francis                 Expires Sept. 1, 2001                   Page 3
                         IPv6 Site Definition             Apr. 1, 2001 
   Fortunately, this can be done automatically with GPS equipment.  
   (They may be other benefits to routers knowing their position, but 
   these are outside the scope of this document.) 
   The router configured with the bearing of the site includes it in 
   its router advertisements.  It also includes its own position in its 
   router advertisements.  Every router, upon receiving a router 
   advertisement, determines if it is the site or not, and if its 
   neighbor is in the site or not.  If it is, it in turns includes the 
   site bearing and its location in its advertisements.  If not, it 
   includes only its location.  In this way, every router will know 
   what site it is in and what site its neighbors are in.  Thusly, site 
   boundaries are autoconfigured.  
5  Security Considerations  
   While there may be new failure modes introduced by autoconfigured 
   site boundaries, there are no new security considerations resulting 
   from this work.   
6  Copyright 
   The following copyright notice is copied from RFC 2026 [Bradner,  
   1996], Section 10.4, and describes the applicable copyright for this  
   Copyright (C) The Internet Society XXX 0, 0000. All Rights Reserved. 
   This document and translations of it may be copied and furnished to  
   others, and derivative works that comment on or otherwise explain it  
   or assist in its implementation may be prepared, copied, published  
   and distributed, in whole or in part, without restriction of any  
   kind, provided that the above copyright notice and this paragraph  
   are included on all such copies and derivative works.  However, this  
   document itself may not be modified in any way, such as by removing  
   the copyright notice or references to the Internet Society or other  
   Internet organizations, except as needed for the purpose of  
   developing Internet standards in which case the procedures for  
   copyrights defined in the Internet Standards process must be  
   followed, or as required to translate it into languages other than  
   The limited permissions granted above are perpetual and will not be  
   revoked by the Internet Society or its successors or assignees. 
   This document and the information contained herein is provided on an  
Francis                 Expires Sept. 1, 2001                   Page 4
                         IPv6 Site Definition             Apr. 1, 2001 
7  Intellectual Property 
   The following notice is copied from RFC 2026 [Bradner, 1996],  
   Section 10.4, and describes the position of the IETF concerning  
   intellectual property claims made against this document. 
   The IETF takes no position regarding the validity or scope of any  
   intellectual property or other rights that might be claimed to  
   pertain to the implementation or use other technology described in  
   this document or the extent to which any license under such rights  
   might or might not be available; neither does it represent that it  
   has made any effort to identify any such rights.  Information on the  
   IETF's procedures with respect to rights in standards-track and  
   standards-related documentation can be found in BCP-11.  Copies of  
   claims of rights made available for publication and any assurances  
   of licenses to be made available, or the result of an attempt made  
   to obtain a general license or permission for the use of such  
   proprietary rights by implementers or users of this specification  
   can be obtained from the IETF Secretariat. 
   The IETF invites any interested party to bring to its attention any  
   copyrights, patents or patent applications, or other proprietary  
   rights which may cover technology that may be required to practice  
   this standard.  Please address the information to the IETF Executive  
8  References 
   1   "IPv6 Scoped Address Architecture ", draft-ietf-ipngwg-scoping-
   2   S. Bradner, "Key words for use in RFCs to Indicate Requirement 
   Levels", BCP 14, RFC 2119, March 1997. 
Francis                 Expires Sept. 1, 2001                   Page 5