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Network Working Group                                      S. Jiang, Ed.
Internet-Draft                              Huawei Technologies Co., Ltd
Intended status: Informational                                    Q. Sun
Expires: November 29, 2013                                 China Telecom
                                                               I. Farrer
                                                     Deutsche Telekom AG
                                                                   Y. Bo
                                            Huawei Technologies Co., Ltd
                                                            May 28, 2013


                  A Framework for Semantic IPv6 Prefix
                     draft-jiang-semantic-prefix-05

Abstract

   This document describes a framework method that network operations
   may use their addresses.  Network operators, who have large IPv6
   address space, may choose to embedded some semantics into IPv6
   addresses by assigning additional significance to specific bits
   within the prefix.  By embedded semantics into IPv6 prefixes, the
   semantics of packets can be inspected easily.  Routers and other
   intermediary devices can easily apply relevant policies as required.
   Packet-level differentiation can also enable flow-level and user-
   level differentiation.  Consequently, the network operators can
   accordingly treat network packets differently and efficiently.  The
   management and maintenance of networks can be much simpler.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on November 29, 2013.

Copyright Notice





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   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Existing Approaches to Traffic Differentiation  . . . . . . .   3
     2.1.  Differentiated Services . . . . . . . . . . . . . . . . .   3
     2.2.  Deep Packet Inspection  . . . . . . . . . . . . . . . . .   4
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Technical Framework of Semantic IPv6 Prefix . . . . . . . . .   4
     4.1.  Justifcation for Semantics with the IPv6 Prefix . . . . .   5
     4.2.  The Semantic Prefix Domain  . . . . . . . . . . . . . . .   6
     4.3.  The Embedded Semantics  . . . . . . . . . . . . . . . . .   7
     4.4.  Network Operations Based on Semantic Prefix . . . . . . .   7
   5.  Potential Benefits  . . . . . . . . . . . . . . . . . . . . .   8
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   7.  Change Log (removed by RFC editor)  . . . . . . . . . . . . .   9
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     10.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Appendix A.  An ISP Semantic Prefix Example . . . . . . . . . . .  11
     A.1.  Function Type Semantic Bits . . . . . . . . . . . . . . .  12
     A.2.  Network Device Type Bits within Network Device Address
           Space . . . . . . . . . . . . . . . . . . . . . . . . . .  12
     A.3.  Subscriber Type Bits within Subscriber Address Space  . .  13
     A.4.  Service Platform Type Bits within Service Platform
           Address Space . . . . . . . . . . . . . . . . . . . . . .  14
   Appendix B.  An Enterprise Semantic Prefix example  . . . . . . .  15
   Appendix C.  A Multi-Prefix Semantic example  . . . . . . . . . .  16
   Appendix D.  Gaps for complex semantic scenarios  . . . . . . . .  17
     D.1.  Semantic Notification in the Network  . . . . . . . . . .  17
     D.2.  Semantic Relevant Interactions between Hosts and the
           Network . . . . . . . . . . . . . . . . . . . . . . . . .  17
   Appendix E.  Topics for Future Work . . . . . . . . . . . . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19



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1.  Introduction

   As the global Internet expands, it is being used for an increasingly
   diverse range of services.  These services place differentiated
   requirements upon packet delivery networks meaning that Internet
   Service Providers and enterprises need to be aware of more
   information about each packet in order to best meet a specific
   service's needs.

   Within a specific prefix, source/destination location information is
   used for routing decisions.  However, user types, service types,
   applications, security requirements, traffic identity types, quality
   requirements and other criteria may also be relevant parameters which
   a network operator may wish to use to treat packets differently and
   efficiently.  Packet-level differentiation can also be used for flow-
   level and user-level differentiation.

   However, almost all of the above mentioned criteria are not expressed
   explicitly within an packet.  Hence, it is difficult for network
   operators to identify from packet level.

   This informational document only discusses the usage of semantics
   within a single network, or group of interconnected networks which
   share a common addressing policy, referred to as a Semantic Prefix
   Domain.

   The informational document is NOT intended to suggest the
   standardization of any common global semantics.

2.  Existing Approaches to Traffic Differentiation

   There are several existing approaches which have been developed that
   can assist operators in identifying and marking traffic.  These
   solutions were mainly developed in the IPv4 era, where the IP address
   is used as a host locator and little else.  The limited capacity of a
   32-bit IPv4 address provides very little room for encoding additional
   information.  Correspondingly, these approaches are indirect,
   inefficient and expensive for operators.

2.1.  Differentiated Services

   Quality of Service (QoS) based on and Differentiated Services
   [RFC2474] is a widely deployed framework specifying a simple,
   scalable and coarse-grained mechanism for classifying and managing
   network traffic.  But in a service provider's network, DiffServ
   codepoint (DSCP) values cannot be trusted when they are set by the
   customer as these are arbitrary values.




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   In real-world scenarios, ISPs deploy "remarking" points at the
   customer edge of their network, re-classifying received packets by
   rewriting the DSCP field according to local policy using information
   such as the source/destination address, IP protocol number and
   transport layer source/destination ports.

   The traffic classification process leads to increased packet
   processing overhead and complexity at the edge of the service
   provider's network.

   The DSCP in the IPv6 header traffic class field allows 6-bits for
   encoding service provider specific information related to the
   contents of the packet.  Whilst this is a useful part of an overall
   packet differentiation architecture, the relative small number of
   available bits (when compared to the available number of bits within
   the service providers prefix) means that it cannot be used in
   isolation.

2.2.  Deep Packet Inspection

   Deep Packet Inspection (DPI) may also be used by ISPs to learn the
   characteristics of users packets.  This involves looking into the
   packet well beyond the network-layer header to identify the specific
   application traffic type.  Once identified, the traffic type can be
   used as an input for setting the packet's DSCP or other actions.

   But DPI is expensive both in processing costs and latency.  The
   processing costs means that dedicated infrastructure is necessary to
   carry out the function.  The incurred latency may be too much for use
   with any delay/jitter sensitive applications.  As a result, DPI is
   difficult for large-scale deployment and it's usage is usually
   limited to small and specific functions in the network.

3.  Terminology

   The following terms are used throughout this document:

   Semantic Prefix:  A flexible-length IPv6 prefix which embeds certain
      semantics.

   Semantic Prefix Domain:  A portion of the Internet over which a
      consistent semantic-prefix based policy is in operation.

   Semantic Prefix Policy:  A policy based on the embedded semantics
      within IPv6 prefix.

4.  Technical Framework of Semantic IPv6 Prefix




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   The IPv6 address can explicitly express semantics due to its large
   address space.  This can be used by network operators to embed
   certain pre-defined semantics into an address so that intermediate
   devices can easily apply relevant forwarding operations each packet
   based solely on network layer source and destination address
   information.

   This document describes a technical framework for embedding semantics
   into IPv6 prefixes so that network devices can process and forward
   packets based on these semantics.  This approach diverts much network
   complexity to the planning and management of IPv6 address and IP
   address based policies.  It indeed simplifies the management of ISP
   networks.

   A network operator should first carefully plan/design its IPv6
   address schema, in which useful semantics (see Section 4.3) are
   embedded into prefix.  It then delegates prefixes with correspondent
   semantics to users.  The users generate their IPv6 addresses based on
   assigned prefixes.  Then, when the IPv6 stack on the user devices
   forms packets, the source addresses comprise compliance semantics.
   The filters on the edge router drop packets which does not compliant
   with assigned prefixes.

   Semantic prefix definitions are only meaningful within a domain which
   implements a single policy (see Section 4.2).  Different service
   providers may make very different choices regarding the specific
   semantics which are relevant to their networks.  Therefore, it is not
   possible or desirable to attempt to standardize a general semantic
   prefix policy.

   Forwarding policies, security isolation and other network operations
   (see Section 4.4) can be easily applied according to semantics, which
   self-expressed by the source address of every packet.  Also, the
   semantics of the destination address may take in account if the
   destination is in the same Semantic Prefix Domain or the peer
   Semantic Prefix Domain whose semantics has been notified.

4.1.  Justifcation for Semantics with the IPv6 Prefix

   Although the interface identifier portion of an IPv6 address has
   arbitrary bits and extension headers can carry significantly more
   information, these fields can not be trusted by network operators.
   Users may easily change the setting of interface identifier or
   extension header in order to obtain undeserved priorities/privileges,
   while servers or enterprise users may be much more self-restricted
   since they are charged accordingly.





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   Prefix is almost the only thing a network operator can trust in an IP
   packet.  Semantic prefix approach does require the deployment of
   access control filters.  The packets with the noncompliance source
   addresses should be filtered.  The prefix is delegated by the network
   and therefore the network is able to detect any undesired
   modifications and filter the packet accordingly.  This also makes it
   possible for the service provider to increase the level of trust in a
   customer-generated packet.  If the packet has an incorrectly set
   source or destination address, then a session will simply fail to
   establish.

4.2.  The Semantic Prefix Domain

   A Semantic Prefix Domain is analogous to a Differentiated Services
   Domain [RFC2474].  It can be described as a portion of the Internet
   over which a consistent set of semantic-prefix-based policies are
   administered in a coordinated fashion.  Some of the characteristics
   of a single Semantic Prefix Domain could represent include:

   a.  Administrative domains

   b.  Autonomous systems

   c.  Trust regions

   d.  Network technologies

   e.  Hosts

   f.  Routers

   g.  User groups

   h.  Services

   i.  Traffic groups

   j.  Applications

   An enterprise Semantic Prefix Domain may span several physical
   networks and traverse ISP networks.  However, when an interim network
   is traversed (such as when an intermediary ISP is used for
   interconnectivity), the relevance of the semantics is limited to
   network domains that share a common Semantic Prefix Policy.

   The selection of semantics vary between different Semantic Prefix
   Domains.  Network operators should choose semantics according to
   their network and service management needs.  If an ISP has several



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   non-contiguous address blocks, they may be organized as a single
   Semantic Prefix Domain if the same Semantic Prefix Policy is shared
   across these non-contiguous address blocks.

   A Semantic Prefix Domain has a set of pre-defined semantic
   definitions, which are only meaningful locally.  Without an efficient
   semantics notification, exchanging mechanism or service agreement,
   the definitions of semantics are only meaningful within local
   Semantic Prefix Domain.  Manual interactions between network
   operators may also work out.  However, this may involve trust models
   among network operators.

   Sharing semantic definition among Semantic Prefix Domains enables
   more semantic based network operations.

4.3.  The Embedded Semantics

   The size of the operator assigned prefix means that there is
   potentially much more scope for embedding semantics than has
   previously been possible.  The following list describes some
   suggested semantics which may be useful to network operators besides
   source/destination location:

   a.  User types

   b.  Applications

   c.  Security domain

   d.  Traffic identity types

   e.  Quality requirements

   Consideration must also be given to the complexity that is created
   within the semantic prefix policy.  Whilst it may be desirable to
   encode as much information within the prefix so that it is possible
   to have a high level of granularity, this can come at the expense of
   future addressing flexibility and could also lead to a high amount of
   address wastage.  In the same time, embedding too many semantics may
   waste addressing space and induce semantic overlap.  It should be
   taken into careful consideration on semantics definition.

4.4.  Network Operations Based on Semantic Prefix

   Based on the explicit semantics from the addresses of every packet,
   many network operations can be applied.  Comparing with traditional
   operations, these operations are easier to realize and stable.
   Although the detailed operation are various depending on various



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   embedded semantics, the network operations based on semantic prefix
   can be abstracted into following categories:

   a.  Statistic based on certain semantic.  Any embedded semantic can
       be set as a statistic condition.  In other word, any embedded
       semantic can be measured independently.

   b.  Differentiate packet processing.  Many packet processing
       operations can be applied based on the semantic differentiation,
       such as queueing, path selection, forwarding to certain process
       devices, etc.

   c.  Security isolation.  A set of packet filters that are based on
       semantic can fulfil network security isolation.

   d.  Access control.  Resource access, authentication, service access
       can be based on semantic directly.

   e.  Resource allocation.  Resources, such as bandwidth, fast queue,
       cache, etc., can be allocated or reserved for certain semantic
       users/packets.

   f.  Virtualization.  Within a Semantic Prefix Domain, it would be
       easy to organize a virtual network, in which all the nodes have
       been assigned same semantic identifier so that the packets from
       them can be distinguished from other virtual networks.

5.  Potential Benefits

   Depending on embedded semantics, various beneficial scenarios can be
   expected.

   a.  Simplified measurement and statistics gathering: the semantic
       prefix provides explicit identifiers which can be used for
       measurement and statistical information collection.  This can be
       achieved by checking certain bits of the source and/or
       destination address in each packet.

   b.  Simplified flow control: by applying policies according to
       certain bit values, packets carrying the same semantics in their
       source/destination addresses can.

   c.  Service segregation: when service related information is encoded
       within the semantic prefix, this can be used to create simple
       access-control lists which can be applied uniformly across all
       network devices.  This means that it is easy to





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   d.  Policy aggregation: the semantic prefix allows many policies to
       be aggregated according to the same semantics within the policy
       based routing system [RFC1104].

   e.  Easy dynamic reconfiguration of semantic oriented policy: network
       operators may want to dynamically change the policy actions that
       are operated on certain semantic packets.  The semantic prefix
       allows such changes be operated easily, as only a small number of
       consistent policy rules need to be updated on all devices within
       the semantic prefix domain.

   f.  Application-aware routing: embedding application information into
       IP addresses is the simplest way to realize application aware
       routing.

   g.  Easy user behavior management: based on the user type reading
       from the addresses, any improper user behaviors can be easy
       detected and automatically handle by network policies.

   h.  Easy network resources access rights management: the
       authentication of access right may already be embedded into the
       addresses.  Simple matching policies can filter improper access
       requests.

   i.  Easy virtualization: virtual network based on any semantics can
       be easily deployed using the semantic prefix mechanism.

6.  IANA Considerations

   This document has no IANA considerations.

7.  Change Log (removed by RFC editor)

   draft-jiang-semantic-prefix-05: reword to emphasis this mechanism is
   a (not the) method that network operators use their addresses; add
   text to clarify the increased trust is actually from the deployment
   of source address filter, which is a compliance requirement by
   semantic prefix; restructure the document, move examples and gap
   analysis into appendixes, reorganize most content into a frame
   section; add summarized description for framework at the beginning of
   Section 4; add description for network operations based on semantic
   prefix; add a new coauthor who contributes an enterprise semantic
   prefix network example; combine most of draft-sun-v6ops-semantic-
   usecase into the draft as ISP example in appendix; 2013-5-28.

   draft-jiang-semantic-prefix-04: add new coauthor, re-organize the
   content, and refine the English, 2013-1-31.




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   draft-jiang-semantic-prefix-03: add the concept of hierarchical
   Semantic Prefix Domain and more gap analysis, 2012-10-22.

   draft-jiang-semantic-prefix-02: resubmitted to v6ops WG.  Removed
   detailed examples and recommendations for semantics bits, 2012-10-15.

   draft-jiang-semantic-prefix-01: added enterprise considerations and
   scenarios, emphasizing semantics only for local meaning and no intend
   to standardize any common global semantics, 2012-07-16.

   draft-jiang-semantic-prefix-00: original version, 2012-07-09

8.  Security Considerations

   Embedding semantics in prefix is actually exposing more information
   of packets explicit.  These informations may also provide convenient
   for malicious attackers to track or attack certain type of packets.
   If networks announce their local prefix semantics to their peer
   networks, it may also increase the vulnerable risk.

   Prefix-based filters should be deployed, in order to protect against
   address spoofing attacks or denial of service for packets with forged
   source addresses.

9.  Acknowledgements

   Useful comments were made by Erik Nygren, Nick Hilliard, Ray Hunter,
   David Farmer, Fred Baker, Joel Jaeggli, John Curran and other
   participants in the V6OPS working group.

10.  References

10.1.  Normative References

   [RFC1104]  Braun, H., "Models of policy based routing", RFC 1104,
              June 1989.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2474]  Nichols, K., Blake, S., Baker, F., and D.L. Black,
              "Definition of the Differentiated Services Field (DS
              Field) in the IPv4 and IPv6 Headers", RFC 2474, December
              1998.

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.



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

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007.

   [RFC6724]  Thaler, D., Draves, R., Matsumoto, A., and T. Chown,
              "Default Address Selection for Internet Protocol Version 6
              (IPv6)", RFC 6724, September 2012.

10.2.  Informative References

   [RFC5014]  Nordmark, E., Chakrabarti, S., and J. Laganier, "IPv6
              Socket API for Source Address Selection", RFC 5014,
              September 2007.

   [RFC5401]  Adamson, B., Bormann, C., Handley, M., and J. Macker,
              "Multicast Negative-Acknowledgment (NACK) Building
              Blocks", RFC 5401, November 2008.

Appendix A.  An ISP Semantic Prefix Example

   This ISP semantic prefix example is abstracted from a real ISP
   address architecture design.

   Note: for now, this example only covers unicast address within IP
   Version 6 Addressing Architecture [RFC4291].

   For ISPs, several motivations to use semantic prefixes are as
   follows:

   a.  Network Device management: Separated and specialized address
       space for network device will help to identify the network device
       among numerous addresses and apply policy accordingly.

   b.  Differentiated user management: In ISPs' network, different kinds
       of customers may have different requirements for service
       provisioning.

   c.  High-priority service guarantee: Different priorities may be
       divided into apply differentiated policy.

   d.  Service-based Routing: ISPs may offer different routing policy
       for specific service platforms .e.g.video streaming, VOIP, etc.



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   e.  Security Control: For security requirement, operators need to
       take control and identify of certain devices/customers in a quick
       manner.

   f.  Easy measurement and statistic: The semantic prefix provides
       explicit identifiers for measurement and statistic.

   These requirements are largely falling into two categories: some is
   regarding to the network device features, and the others are related
   to services provision and subscriber identification.  The functional
   usage of the semantics for the two categories are quite different.
   Therefore, an ISP semantic IPv6 prefix example is designed as a two-
   level hierarchical architecture, in which the first level is the
   function types of prefixes, and the second level is the further usage
   within an specific prefix type.

A.1.  Function Type Semantic Bits

   Function Type (FT): the value of this field is to indicate the
   functional usage of this prefix.  The typical types for operators
   include network device, subscriber and service platform.

   +--------+--------+------------------------------------------------+
   |        | FT     |                                                |
   +--------+--------+------------------------------------------------+
           /          \
          +------------+------------+
          |000:     network device  |
          |000~010: service platform|
          |011~101: subscriber      |
          |110:     reserved        |
          +-------------------------+

                        Function Type Bits Example

                                 Figure 1

   The portion of each type should be estimated according to the actual
   requirements for operators, in order to use the address space most
   efficiently.  Within the above FT design, the whole ISP IPv6 address
   space is divided into four parts: the network device address space (1
   /8 of total address space), the service platform address space (2/8
   of total address space), the subscriber address space (3/8 of total
   address space), and a reserved address space (1/8 of total address
   space) for future usage.

A.2.  Network Device Type Bits within Network Device Address Space




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   Network Device Type (NDT) indicates different types of network
   devices.  Normally, one operator may have multiple networks,
   e.g.backbone network, mobile network, ISP brokered service network,
   etc.  Using NDT field to indicate specific network within an operator
   may help to apply some routing policies.  Locating NDT bits in the
   left-most bits means that a single, simple access- control list
   implemented across all networking devices would be enough to enforce
   effective traffic segregation.  The Locator field is followed behind
   NDT.

   +--------+--------+------+-----------------------------------------+
   |        | FT(000)|  NDT |   Locator    |   Network Device bits    |
   +--------+--------+------+-----------------------------------------+
                    /        \
                   /          \
                  +------------+-----+
                  |000~001:  SubNet 1|
                  |010~110:  SubNet 2|
                  |111:      Reserved|
                  +------------------+

                     Network Device Type Bits Example

                                 Figure 2

   The portion of each subnet type should be estimated according to the
   actual requirements for operators, in order to use the address space
   most efficiently.  Within the above NDT design, SubNet 1 is assigned
   2/8 of the network device address space, SubNet 2 is assigned 5/8,
   and 1/8 is reserved.

A.3.  Subscriber Type Bits within Subscriber Address Space

   Subscriber Type (ST) indicates different types of subscribers, e.g.
   wireline broadband subscriber, mobile subscriber, enterprise, WiFi,
   etc.  This type of prefix is allocated to end users.  Further,
   division may be taken on subscriber's priorities within a certain
   subscriber type.

   The Locator field within subscriber address space is put before ST
   for better routing aggregation.

   +--------+--------+---------------+------+-------------------------+
   |        | FT(011)|  Locator      |  ST  |   Subscriber bits       |
   +--------+--------+---------------+------+-------------------------+
                                    /        \
                                   /          \
                       +----------+------------+---------------+



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                       |0000~0011: broadband access subscriber |
                       |0100~0111: mobile subscriber           |
                       |1000~1001: enterprise                  |
                       |1010~1011: WiFi subscriber             |
                       |1100~1111: Reserved                    |
                       +---------------------------------------+

                       Subscriber Type Bits Example

                                 Figure 3

   The portion of each subscriber type should be estimated according to
   the actual requirements for operators, in order to use the address
   space most efficiently.  Within the above ST design, the broadband
   access subscriber type is assigned 4/16 of the subscriber address
   space, the mobile subscriber is assigned 4/16, enterprise type and
   WiFi subscriber type are assigned 2/16 each, and 2/16 is reserved.

A.4.  Service Platform Type Bits within Service Platform Address Space

   Service Platform Type (SPT) indicates typical service platforms
   offered by operators.  This field may have scalability problem since
   there are numerous types of services . It is recommended that only
   aggregated service platform types should be defined in this field.
   This type of prefix is usually allocated to service platforms in
   operator's data center.

   +--------+--------+---------------+------+-------------------------+
   |        | FT(001)|  Locator      |  SPT |   Service  bits         |
   +--------+--------+---------------+------+-------------------------+
                                    /        \
                                   /          \
                       +----------+------------+---------------+
                       |000~001: Self-running service platform |
                       |001~011: Tenant service platform       |
                       |100~101: Independent service platform |
                       |110~111: Reserved                      |
                       +---------------------------------------+

                    Service Platform Type Bits Example

                                 Figure 4

   The portion of each subnet type should be estimated according to the
   actual requirements for operators, in order to use the address space
   most efficiently.





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Appendix B.  An Enterprise Semantic Prefix example

   This enterprise semantic prefix example is also abstracted from an
   ongoing enterprise address architecture design.  This example is
   designed for a realtime video monitor network across a city region.
   The semantic prefix solution is planning to be deployed along with a
   strict authorization system.

   Note: this example only covers unicast address within IP Version 6
   Addressing Architecture [RFC4291].

   For this example, the below semantics are important for the network
   operation and require different network behaviors.

   a.  Terminal type: there are two terminal types only: monitor cameras
       or video receivers.  They are estimated to have similar number.
       Network devices use another different address space.

   b.  Geographic location: the city has been managed in a three-level
       hierarchical regionalism: district, area and street.  Each level
       has less than 28 sub-regions.  This can also be considered as a
       replacement of topology locator within this specific network.

   c.  Authorization level: the network operator is planning to
       administrate the authorization in three or four levels.  An
       receiver can access the cameras that are the same or lower
       authorization level.

   d.  Civilian or police/government.

   e.  Device attribute: this indicates the attribute of a camera
       device.  The attribute is expressed in an abstract way, such as
       road traffic, hospital, nursery, bank, airport, etc.  The
       abstracted attribute type is designed to be less than 64.

   f.  Receiver Attribute: this indicates the attribute of a video
       receiver.  The attribute is based on the receiver group, such as
       police, firefighter, local security, etc.  The attribute/receiver
       group type is designed to be less than 128.

   This example enterprise network has obtained a /32 address block from
   ISP.  There is another /48 dedicated for network devices.

   The first bit is Terminal type, which indicates terminal type.

      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       ISP assigned block                      |



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     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |T|    Geographic   Locator     | AL|C|Device Attr|  Device Bit |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               A semantic prefix design example for cameras

                                 Figure 5

   3-level hierarchical geographic locator takes 15 bits (each level 5
   bits, 32 sub-regions).  Authorization level takes 2 bits and 1 bit
   differentiates civilian or police/government.  6 bits is assigned for
   device attribute.

      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       ISP assigned block                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |T| GeoLoc  | AL|C|Receiver Attr|  Topology Locator |ReceiverBit|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           An semantic prefix design example for video receivers

                                 Figure 6

   The receiver is not as much as geographically distributed as cameras.
   Therefore, Geographic locator is only detailed to district level.
   Topology locator is needed for network forwarding and aggregation
   within a district.  It is assigned 10 bits.  Authorization level bits
   and civilian bit are the same with camera address space.  Receive
   attribute takes 7 bits, giving it is designed to be up to 128.

Appendix C.  A Multi-Prefix Semantic example

   A multiple-site enterprise may have been assigned several prefixes of
   different lengths by its upstream ISPs.  In this situation, in order
   to create a single, contiguous Semantic Prefix Domain, it is
   necessary to base the semantic prefix policy on the longest assigned
   prefix to ensure that there in enough addressing space to encode a
   consistent set of semantics across all of the assigned prefixes.

   In this example, an enterprise has received a /38 address block for
   one site (A) and a /44 for a second site (B) . They can be organized
   in the same Semantic Prefix Domain.  The most-left 18 (site A) and 12
   (site B) bits are allocated as locator.  It provides topology based
   network aggregation.  The 8 right-most bits (from bits 56 to 63) are
   assigned as the semantic field.  In this design, the multiple-site
   enterprise that has been assigned two prefixes of different lengths
   can be organized as the same Semantic Prefix Domain.  The semantic



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   and the Semantic Prefix Domain can traverse the intermediate ISP
   networks, or even public networks.

   The similar situation may happen on ISPs in the future, when an ISP
   used up its assigned address space, or built up multiple networks in
   different places.

Appendix D.  Gaps for complex semantic scenarios

   The simplest semantic prefix model is to embed only abstracted user
   type semantics into the prefix.  Current network architectures can
   support this as each subscriber is still assigned a single prefix,
   while they are not notified the semantic within it.

   In order to maximise the benefits of the semantic prefix design,
   additional functions are needed to allow semantic relevant operations
   in networks and semantic relevant interactions with hosts.

   IPv6 provides a facility for multiple addresses to be configured on a
   single interface.  This creates a precondition for the approach that
   user chooses addresses differently for different purposes/usages.

D.1.  Semantic Notification in the Network

   In order to manage semantic prefixes and their relevant network
   actions, the network should be able to notify semantics along with
   prefix delegation.

   When an prefix is delegated using a DHCPv6 IA_PD [RFC3633], the
   associated semantics should also be propagated to the requesting
   router.  This is particularly useful for autonomic process when a new
   device is connected.

D.2.  Semantic Relevant Interactions between Hosts and the Network

   The more that semantics are embedded into a prefix, the more that
   complicated functions are needed for semantic relevant interactions
   between hosts and the network, such as prefix delegation, host
   notification and address selections, etc.

   In practice, a single host may belong to multiple semantics.  This
   means that several IPv6 addresses are configured on a single physical
   interface and should be selected for use depending on the service
   that a host wishes to access.  A certain packet would only serve a
   certain semantic.

   The host's IPv6 stack must have a mechanism for understanding these
   semantics in order to choose right source address when forming a



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   packet.  If the embedded semantic is application relevant,
   applications on the hosts should also be involved in the address
   choosing process: the host IPv6 stack reports multiple available
   addresses to the application through socket API (one example is "IPv6
   Socket API for Source Address Selection" [RFC5014]).  The application
   then needs to apply the semantic logic so that it can correctly
   select from the offered candidate addresses.

   Although [RFC6724] provides an algorithm for source address
   selection, some semantic prefix policies may conflict with this
   algorithm.  In this case, the source address selection mechanism may
   also further supporting functions to be developed.

Appendix E.  Topics for Future Work

   There are several areas in which the semantic prefix could be
   extended in order to increase the usefulness and applicability of the
   concept.  They are complementarity besides the main framework.  These
   are being described here as topics for possible future work.  Each of
   them may deserve a separated document for technical details.

   - Dynamic Policy Configuration

   Dynamic policy configuration would simplify the distribution of
   policy across devices in the semantic prefix domain.  New functions
   or protocol extension are needed to enable dynamic changes to the
   policy actions in operation on certain semantic packets.

   - Semantics Announcements to peer networks

   A network may announce all, or some of its Semantic Prefix Policy to
   connected peer networks.  This could be used to enable more dynamic
   configuration and enable traffic from different semantic prefix
   domains to traverse different networks whilst having the same
   semantic prefix policy applied.  To achieve this automatically by
   message exchanging would require new functions or protocol
   extensions.

   - Extension of Prefix Semantics beyond the left-most 64-bits

   The prefix concept refers here to the left-most bits in the IP
   addresses delegated by the network management plane.  The prefix
   could be longer than 64-bits if the network operators strictly manage
   the address assignment by using Dynamic Host Configuration Protocol
   for IPv6 (DHCPv6) [RFC3315] (but in this case standard StateLess
   Address AutoConfiguration - SLAAC [RFC4862] cannot be used).





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Authors' Addresses

   Sheng Jiang (editor)
   Huawei Technologies Co., Ltd
   Q14, Huawei Campus, No.156 BeiQing Road
   Hai-Dian District, Beijing  100095
   P.R. China

   Email: jiangsheng@huawei.com


   Qiong Sun
   China Telecom
   Room 708, No.118, Xizhimennei Street
   Beijing 100084
   P.R. China

   Email: sunqiong@ctbri.com.cn


   Ian Farrer
   Deutsche Telekom AG
   Bonn 53227
   Germany

   Email: ian.farrer@telekom.de


   Yang Bo
   Huawei Technologies Co., Ltd
   Q21, Huawei Campus, No.156 BeiQing Road
   Hai-Dian District, Beijing  100095
   P.R. China

   Email: boyang.bo@huawei.com















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