Native Short Addresses for the Internet Edge
draft-li-native-short-addresses-00

Document Type Active Internet-Draft (individual)
Authors Guangpeng Li  , Sheng Jiang  , Donald Eastlake 
Last updated 2021-02-21
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Network Working Group                                              G. Li
Internet-Draft                                       Huawei Technologies
Obsoletes: draft-jiang-asymmetric-                              S. Jiang
           ipv6-04 (if approved)            Huawei Technologies Co., Ltd
Intended status: Informational                           D. Eastlake 3rd
Expires: August 24, 2021                                       Futurewei
                                                       February 20, 2021

              Native Short Addresses for the Internet Edge
                   draft-li-native-short-addresses-00

Abstract

   This document describes a new approach to IP header compression
   including native short addresses adoption for use in scenarios where
   minimizing packet size is crucial but routing performance must be
   maximised.

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   This Internet-Draft will expire on August 24, 2021.

Copyright Notice

   Copyright (c) 2021 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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   8.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   9.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
   Appendix A. . . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.

   The large address space of IPv6 is essential for the massive
   expansion of the network edge that will be caused by "Internet of
   Things" (IoT) technology over low-power or 5G links.  However, the
   size of a raw IPv6 packet header causes difficulty due to the small
   maximum transmission units (MTU) allowed by typical low-power, low-
   cost link layers.  For 5G, the importance of header overhead in small
   packets is discussed in [NGMN-5G].  Thus header compression,
   including address compression, is an important issue.  This decreases
   the size of raw packets, but compressed IP addresses are not
   routeable except by decompressing them completely in every forwarding
   node.  There are two issues here.  The first is the extra computation
   resource needed for compressing or decompressing in constrained IoT
   nodes.  The second is that full-length IPv6 routing will consume more
   memory to store routing tables and packet queues (assuming that
   routing is not bypassed by tunnelling).  Such resource consumption is
   very undesirable in constrained nodes with limited storage, CPU
   power, and battery capacity.

   To mitigate these issues, here we propose a solution enabling the
   shortening of IPv6 addresses inside packets, and the routing of
   packets according to short addresses, without needing the overhead of
   a decompression step prior to route lookup.  Considering that the
   scale and size of edge networks may vary widely, different lengths of
   short address can be used in different domains.

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   As an illustrative example, consider an edge network which is known
   to never require more than a few hundred nodes, which in most cases
   will communicate either with each other, or with application layer
   gateways to the rest of the Internet.  Rather than needing 128-bit
   addresses, such a network could very well operate with 16-bit
   addresses.  Also, it could very likely operate without needing
   enhancements such as differentiated services, ECN or flow labels.  If
   only IPv6 is supported, the version number field is pointless.  There
   is no reason for IPv6 packets within such a network to contain
   40-byte headers as specified in [RFC8200].  Therefore, the useful
   information could be carried in 8 bytes (see Figure 1).  Furthermore,
   routers within the edge network can route packets directly on 16-bit
   addresses, reducing RIB and FIB sizes and the lookup time.

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Payload Length        |  Next Header  |   Hop Limit   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Source Address        |  Destination Address          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 1

   This work is distinct from previous work on address compression
   [RFC6282] [RFC7400].  Although those solutions tackle the problem of
   small MTU size, they do not address the problem of decompression
   overhead.

   This work is also distinct from the work on static context header
   compression [RFC8724], as discussed in more detail below.

   Finally, this work is distinct from the 6LoWPAN Routing Header
   [RFC8138], which can support truncated addresses in a different way.

2.

   The use of IPv6 naturally implies 128-bit addresses for both source
   and destination.  However, this address size is huge by the standards
   of IoT edge networks.  We propose the use of a context parameter to
   indicate the effective length of the IP address for every node in a
   local domain.  If the effective length is N bits, then all addresses
   in the domain are assumed to be preceded by a common prefix of 128-N
   bits, when a full size IPv6 address is needed.  Any node in the
   domain that needs the full address, such as a gateway node to the
   Internet, can therefore easily synthesize it.  If a client
   communicates with a server that is in the local domain, short
   addresses will be used end-to-end.

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   The address length parameter may be needed by every node in the
   domain.  It can be spread by various techniques:

   The solution operates by shortening IP address fields to save
   overhead.  To enhance this, we propose a new field named Flexible
   Header Encoding (FHE).  It consists of 8 bits, each indicating
   whether the corresponding IPv6 header field [RFC8200] exists.

   The "Version" field is a special case.  In the context of FHE, all
   packets are presumed to be IPv6 so the normal version field has no
   purpose.  The Modified Version field, if present, has the following
   encoded meanings:

   All fields, including the Modified Version field, follow the FHE in
   the same order as in [RFC8200], with no padding.  There are no
   alignment requirements, but when a packet is decompressed to a normal
   IPv6 format, padding options as defined in RFC8200 must be inserted.

   Compared to the illustrative example in Figure 1, the actual packet
   size would therefore be 10 bytes, a considerable improvement on the
   standard 40 bytes.  This method of shortening packets by using the
   FHE header is called Asymmetric IPv6.

   One implication of the above is that the source and destination
   addresses may be elided completely if they are implicit.  Sourceless
   packets were originally suggested in [Crowcroft].

   Figure 2 illustrates an example of the FHE format.  In this example
   the traffic class, flow label and source address are elided, and the
   destination address is truncated to 16 bits.  The modified version
   field could be 0b0001 or 0b0010.

                                                         FHE octet
       Modified                                       +-+-+-+-+-+-+-+-+
       Version                                        |1 0 0 1 1 1 0 1|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |0 0 0 1|       Payload Length          |  Next Header  |  Hop  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Limit | Truncated Destination Address |                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                       |
      |                                                               |
      +               Transport payload                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.........

                                 Figure 2

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   Note that Asymmetric IPv6 does not contain any special handling for
   IPv6 fragmentation, which will operate exactly as described in
   [RFC8200], with Asymmetric IPv6 applied to each fragment packet.
   However, we assume that in IoT deployment scenarios, packets whose
   length exceeds the IPv6 minimum link MTU before applying Asymmetric
   IPv6 will be rare.  If the underlying link layer cannot carry
   complete packets even after applying Asymmetric IPv6 compression, an
   adaptation layer will be necessary exactly as for normal IPv6.

3.

   Truncated intra-domain addresses will be used to identify nodes
   inside the domain.  When a packet is sent from an IoT node to an
   external IPv6 host , the node's intra-domain address, which is unique
   in the domain, will be carried in the source address field.  When the
   packet is forwarded outside the domain by a gateway, the intra-domain
   address will be transformed to a complete IPv6 address.  To achieve
   this, the gateway should will maintain a globally routeable prefix
   for all the nodes in the domain.  When a packet with an intra-domain
   source address is received, the gateway extracts this address and
   concatenates it to the prefix to form a standard, globally unique
   IPv6 address.  Vice versa, when IPv6 packets are received from the
   Internet, the prefix will be removed to recover the intra-domain
   short address.

   There are two options for handling the addresses of external hosts
   within the domain.  One is to use their full IPv6 addresses via
   Modified Version codes 0b0000 and 0b0001.  The other is effectively a
   specialized form of Network Address Translation.  Here, the gateway
   will maintain a dynamic mapping table between synthetic intra-domain
   addresses and IPv6 addresses.  As packets are received, the gateway
   performs the appropriate mapping.  The transformation must be
   checksum-neutral for the transport layer, so the methods designed for
   NAT46 should be adapted [RFC6145].

   It is an engineering choice whether this method is preferable to
   carrying full 128-bit addresses on the IOT side.  Which type of
   resource is more expensive should be seriously considered to choose
   the appropriate ways, e.g. computing, memory, or transmiting in
   various resource-constrained IoT networks.

4.

   Routing mechanisms may readily be adapted to truncated address sizes.
   If there is routing with an FHE domain, we assume that the truncated
   address size will be split into a prefix and an interface identifier,
   but this will not be at the traditional /64 boundary.  If routing
   between different length addresses is required, a suitably modified

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   Forwarding Information Base (FIB) structure is needed, as for any
   variable length addressing scheme.  A truncated address needs to be
   virtually expanded to 128 bits at the router's inbound interface,
   although this may not be the physical implementation.

   A possible routing choice for IOT edge networks is RPL [RFC6550],
   although a more complete survey can be found in [Talwar].

5.

   The simplest approach to address configuration is simply to run
   normal IPv6 procedures (SLAAC or DHCPv6), on the argument that this
   is a rare process and the overhead does not matter.  If the truncated
   address size is less than 64 bits, it will be necessary to use
   shorter interface identifiers than normal, but this is not a major
   change.  Once a node has acquired an IPv6 address and has learned the
   local address length parameter as outlined in Section 2, it can
   continue in FHE mode.

6.

   Although FHE nodes can only talk directly to each other, they are
   essentially a special form of IPv6 node and they can communicate with
   the whole IPv6 Internet via gateways.  The complexity is not greater
   than 6LoWPAN.  If appropriate, the 6LoWPAN adaptation layer [RFC4944]
   could be used, with a specific dispatch type.

7.

   Static Context Header Compression (SCHC) [RFC8724] is a powerful
   mechanism for reducing IPv6 packet size in an IoT application
   environment.  In particular it includes a profile for UDP over IPv6,
   and a somewhat modified version of this profile could achieve much of
   what Asymmetric IPv6 proposes.  In addition, SCHC provides support
   for fragmentation in the case of very small link MTUs.  However, SCHC
   is by design static, and once a context is established the fields to
   be compressed do not change.  Asymmetric IPv6 transmits the FHE and
   Modified Version bytes with every packet, so it provides dynamic
   choice as to which header elements are compressed or elided.

   In a context where the desirable compression is fixed, e.g. every
   address is the same length, the flow label is never used, etc., SCHC
   can used to the same effect as Asymmetric IPv6.  However, if the
   behavior needs to be dynamic, the signaling power of the FHE and
   Modified Version bytes in Asymmetric IPv6 is needed.

   Further study is needed whether the advantages of the two mechanisms
   can be combined.

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8.

   FHE is essentially only a non-cryptographic compression technique so
   it neither adds to nor reduces the intrinsic security of an IPv6
   packet.  The address length parameter is not a secret, since all
   nodes in the domain must know it.  The mechanism for distributing
   this parameter must be no less secure than any other configuration
   mechanism in use.

   Address-based privacy issues must be considered in deciding on the
   address length.  If the number of bits available for the interface
   identifier is significantly less than the 64 currently in use,
   address traceability and guessability will be affected.  However, if
   the traffic with short addresses is confined to within the edge
   network, the privacy issue will be minimized.  [RFC7721] and
   [RFC7217] should be consulted prior to deciding the address length.

9.

   This document makes no request of the IANA.

   NOTE IN DRAFT: If the solution of a 6LoWPAN dispatch type is adopted,
   a suitable assignment request will be added.

10.

   Brian Carpenter as one of the authors of draft-jiang-asymmetric-ipv6
   directly contributes to the former draft's all sections, especially
   for polishing of introduction and solution's description.  As his
   will, this draft absorbs most of the results and will go further
   regarding him as the most important contributor.

11.

   Useful comments were received from Uma Chunduri, Cheng Li, Pascal
   Thubert, Laurent Toutain and others.

12.  References

   [Crowcroft]
              Crowcroft, J. and M. Bagnulo, "SNA: Sourceless Network
              Architecture", 2014.

   [NGMN-5G]  Thibault, I., "5G Extreme Requirements: Operators' views
              on fundamental trade-offs", 2017.

   [Talwar]   Talwar, M., "Routing Techniques and Protocols for Internet
              of Things: a Survey", 2015.

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Appendix A.

Authors' Addresses

   Guangpeng Li
   Huawei Technologies
   Q14, Huawei Campus
   No.156 Beiqing Road
   Hai-Dian District, Beijing  100095
   P.R. China

   Email: liguangpeng@huawei.com

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

   Email: jiangsheng@huawei.com

   Donald Eastlake 3rd
   Futurewei Technologies
   2386 Panoramic Circle
   Apopka
   FL 32703  32703
   United States of America

   Email: d3e3e3@gmail.com

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