Link Identifier Extension to DLEP
draft-dlep-lid-01

Mobile Ad hoc Networks Working Group                           R. Taylor
Internet-Draft                                    Airbus Defence & Space
Intended status: Standards Track                           July 20, 2017
Expires: January 21, 2018

                   Link Identifier Extension to DLEP
                           draft-dlep-lid-01

Abstract

   There exists a class of modems that wish to support the Dynamic Link
   Exchange Protocol (DLEP) [RFC8175] but do not present a single Layer
   2 network domain as required by DLEP.  Such devices may be:

   o  Modems that maintain a varying link to some upstream backbone
      network infrastructure, where the ability to announce link state
      and DLEP metrics is desired, but the concept of a DLEP destination
      router for the backbone does not apply.  Examples of such devices
      can include LTE modems, IEEE 802.11 stations not in ad-hoc mode,
      and some satellite terminals.

   o  Modems that provide Layer 3 wide area network connectivity between
      devices, where individual DLEP destinations do exist, but are not
      directly reachable by MAC address.

   This document introduces an optional extension to the core DLEP
   specification, allowing DLEP to be used between routers and modems
   that operate in this way.

   Note:

   o  This document is intended as an extension to the core DLEP
      specification, and readers are expected to be fully conversant
      with the operation of core DLEP.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any

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   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 January 21, 2018.

Copyright Notice

   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
     1.1.  Requirements  . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Operation . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Identifier Restrictions . . . . . . . . . . . . . . . . .   4
     2.2.  Link Identifier Data Item . . . . . . . . . . . . . . . .   4
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  DLEP Link Identifier Flag . . . . . . . . . . . . . . . .   5
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   The Dynamic Link Exchange Protocol (DLEP) [RFC8175] describes a
   protocol for modems to advertise the status of wireless links between
   reachable destinations to attached routers.  The core specification
   of the protocol assumes that every modem in the radio network has an
   attached DLEP router, and the MAC address of the DLEP interface on
   the router is used to identify the destination in the network for
   purposes of reporting the state and quality of the link to that
   destination.

   This document describes a DLEP Extension allowing modems that do not
   meet the strict requirement that DLEP must be implemented on a single

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   Layer 2 domain to use DLEP to describe link state and quality to one
   or more destinations reachable only at Layer 3.

   To enable routers to take advantage of the DLEP protocol this
   extension adds a single enhancement to the DLEP protocol: A new Link
   Identifier Data Item.  This Data Item replaces the use of the MAC
   Address Data Item whenever the DLEP destination does not have a
   router reachable by MAC address.

   By using the Link Identifier Data Item, the modem implementation can
   announce the link state and quality to a uniquely identified
   destination in the network, either logical or physical, explicitly
   indicating that the destination is not reachable via a single Layer 2
   domain.  A router can use this knowledge to influence any routing or
   flow-control decisions regarding traffic to this destination,
   understanding that such decisions apply at Layer 3.

1.1.  Requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in BCP 14, RFC 2119
   [RFC2119].

2.  Operation

   To use this extension, as with all DLEP extensions, the extension
   MUST be announced during DLEP session initialization.  A router
   advertises support by including the value 'Link Identitifers' (TBD1)
   in the Extension Data Item within the Session Intitialization
   Message.  A modem advertises support by including the value 'Link
   Identitifers' (TBD1) in the Extension Data Item within the Session
   Intitialization Response Message.  If both DLEP peers advertise
   support for this extension then the Link Identifier Data Item MAY be
   used.

   If a modem requires support for this extension in order to describe
   destinations, and the router does not advertise support, then the
   modem MUST NOT include a Link Identifier Data Item in any DLEP
   Message.  However, the modem SHOULD NOT immediately terminate the
   DLEP session, rather it should use session-wide DLEP Data Items to
   announce general information about all reachable destinations via the
   modem.  By doing this, a modem allows a router not supporting this
   extension to at least make a best guess at the state of any reachable
   network.  A modem MUST NOT attempt to re-use the MAC Address Data
   Item to perform some kind of sleight-of-hand, assuming that the
   router will notice the DLEP Peer Type of the modem is special in some
   way.

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   Even when the Link Identifiers extension is in use for a DLEP
   session, both peers MUST support sending and receiving Messages
   concerning DLEP destinations using the standard DLEP MAC Address Data
   Item, as the use of this extension does not alter the representation
   of multicast logical destinations.

2.1.  Identifier Restrictions

   Within a single DLEP session, all identifiers used by this extension,
   both logical and physical, MUST be unique, and MUST be of the same
   octet length as the MAC address of the interface in use for the DLEP
   session, as per MAC Address Data Items.  This removes the need for an
   extra LID length negotiation step during Session Initialization.

   Identifiers MUST NOT be reused, i.e. an indentifier that has been
   used to refer to one destination MUST NOT be recycled to refer to a
   different destination within the lifetime of a single DLEP session.

   The method for generating identifiers is a modem implementation
   matter and out of scope of this document.  Routers MUST NOT make any
   assumptions about the meaning of identifiers, or how identifiers are
   generated.

   Router implementations MUST NOT assume that LIDs will not clash with
   any MAC Address Data Items also in use during the DLEP session, LIDs
   exist in a separate numbering space.

2.2.  Link Identifier Data Item

   The Link Identifier Data Item MAY be used whenever a MAC Address Data
   Item is defined as useable in core DLEP.  A single Link Identifier
   Data Item MUST only be used in place of a single MAC Address Data
   Item.  A Link Identifier Data Item MUST NOT appear in the same DLEP
   Message as a MAC Address Data Item.

    0                   1                   2                   3
    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Item Type                | Length                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Flags        |            Link Identifier...                 :
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD2

   Length:  Same as the MAC Address Data Item in use by the session.

   Flags:  Flags field, defined below.

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   Link Identifier:  The unique identifier of the link destination.
      This identifier has no implicit meaning and is only used to
      discriminate between multiple links.

   The Flags field is defined as:

    0 1 2 3 4 5 6 7
   +-+-+-+-+-+-+-+-+
   |    Reserved   |
   +-+-+-+-+-+-+-+-+

   Reserved:  MUST be zero.  Left for future assignment.

3.  Security Considerations

   As an extension to the core DLEP protocol, the security
   considerations of that protocol apply to this extension.  This
   extension adds no additional security mechanisms or features.

   None of the features introduced by this extension require extra
   consideration by an implementation.

4.  IANA Considerations

   Upon approval of this document, IANA is requested to:

   o  Assign a new value (TBD1) from the Specification Required section
      of the DLEP Extensions Registry, named "Link Identifiers".

   o  Assign a new value (TBD2) from the Specification Required section
      of the DLEP Data Item Type Values Registry, named "Link
      Identifier".

4.1.  DLEP Link Identifier Flag

   Upon approval of this document, IANA is requested to create a new
   DLEP registry, named "Link Identifier Flags".

   The following table provides initial registry values and the
   [RFC5226] defined policies that should apply to the registry:

            +------------+------------------------------------+
            | Bit        | Description/Policy                 |
            +------------+------------------------------------+
            | 0-7        | Unassigned/Specification Required  |
            +------------+------------------------------------+

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5.  References

5.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC8175]  Ratliff, S., Jury, S., Satterwhite, D., Taylor, R., and B.
              Berry, "Dynamic Link Exchange Protocol (DLEP)", RFC 8175,
              DOI 10.17487/RFC8175, June 2017,
              <http://www.rfc-editor.org/info/rfc8175>.

5.2.  Informative References

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <http://www.rfc-editor.org/info/rfc5226>.

Author's Address

   Rick Taylor
   Airbus Defence & Space
   Quadrant House
   Celtic Springs
   Coedkernew
   Newport  NP10 8FZ
   UK

   Email: rick.taylor@airbus.com

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