Link Identifier Extension to DLEP
draft-ietf-manet-dlep-lid-extension-00

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Mobile Ad hoc Networks Working Group                           R. Taylor
Internet-Draft                                    Airbus Defence & Space
Intended status: Standards Track                              S. Ratliff
Expires: June 18, 2018                                        VT iDirect
                                                       December 15, 2017

                   Link Identifier Extension to DLEP
                 draft-ietf-manet-dlep-lid-extension-00

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
   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/.

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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on June 18, 2018.

Copyright Notice

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

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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements  . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Operation . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Identifier Restrictions . . . . . . . . . . . . . . . . .   4
     2.2.  Negotiation . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  New Data Items  . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Link Identifier Length Data Item  . . . . . . . . . . . .   5
     3.2.  Link Identifier Data Item . . . . . . . . . . . . . . . .   6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  DLEP Link Identifier Flag . . . . . . . . . . . . . . . .   7
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

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 requires that the MAC address of the DLEP
   interface on the attached router is used to identify the destination

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   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
   Layer 2 domain to use DLEP to describe link availability and quality
   to one or more destinations reachable beyond a local or remote device
   on the 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 traffic flows via Layer 3.

   A Layer 3 destination may be an attached DLEP router, in the case of
   a modem that provides Layer 3 wide area network connectivity between
   devices, or a logical destination that describes a set of attached
   subnets, when referring to some upstream backbone network
   infrastructure.

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.

2.  Operation

   To refer to a Layer 3 DLEP Destination, the DLEP session participant
   adds a Link Identifier Data Item (Section 3.2) to the relevant
   Destination Message, and (as usual) includes a MAC Address Data Item.
   When paired with a Link Identifier Data Item, the MAC Address Data
   Item describes the MAC address of the node in the network beyond
   which the Layer 3 DLEP Destination resides.  The MAC address MAY
   belong to the DLEP peer modem, if the over-the-air network is not a
   single Layer 2 domain, or MAY be the MAC address of a remote node in
   the Layer 2 domain that has indicated that it has DLEP Destinations
   reachable beyond it.  How such remote destinations are discovered is
   beyond the scope of this specification.

   As only modems are initially aware of Layer 3 DLEP Destinations, Link
   Identifier Data Items referring to a new link MUST first appear in a
   DLEP Destination Up Message from the modem to the router.  Once a
   link has been identified in this way, Link Identifier Data Items MAY
   be used by either DLEP participant during the lifetime of a DLEP
   session.  Because of this, a router MUST NOT send a DLEP Destination
   Announce Message containing a Link Identifier Data Item referring to
   a link that has not been mentioned in a prior DLEP Destination Up
   Message.

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   Because the MAC Address associated with any DLEP Destination Message
   containing a Link Identifier Data Item is not the Layer 2 address of
   the destination, all DLEP Destination Up Messages MUST contain Layer
   3 information.  In the case of modems that provide Layer 3 wide area
   network connectivity between devices, this means one or more IPv4 or
   IPv6 Address Data Items providing the Layer 3 address of the
   destination.  When referring to some upstream backbone network
   infrastructure, this means one or more IPv4 or IPv6 Attached Subnet
   Data Items, for example: '0.0.0.0/0' or '::/0'.  This allows the DLEP
   peer router to understand the properties of the link to those routes.

   When the DLEP peer router wishes to forward packets to the Layer 3
   destination or subnet, the MAC address associated with the link MUST
   be used as the Layer 2 destination of the packet.

2.1.  Identifier Restrictions

   A Link identifier is by default 4 octets in length.  If a modem
   wishes to use an identifier of a different length, it MUST be
   announced using the Link Identifier Length Data Item (Section 3.1)
   contained in the DLEP Session Initialization Response message sent by
   the modem to the router.

   During the lifetime of a DLEP session, the length of Link Identifiers
   MUST remain constant, i.e. the Length field of the Link Identifier
   Data Item must not alter between destinations.

   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.

   Within a single DLEP session, all link identifiers MUST be unique per
   MAC Address.  This means that a Layer 3 DLEP Destination is uniquely
   identified by the pair: {MAC Address,Link Id}.

   Identifiers MUST NOT be reused, i.e. a {MAC Address,Link Id} pair
   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.

2.2.  Negotiation

   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 Identifiers' (TBD1),
   Section 5, in the Extension Data Item within the Session
   Initialization Message.  A modem advertises support by including the

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   value 'Link Identifiers' (TBD1) in the Extension Data Item within the
   Session Initialization 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.

3.  New Data Items

   This extension introduces two new DLEP Data Items: the Link
   Identifier Data Item (Section 3.2) used to identify a Layer 3 link at
   or beyond a destination, and the Link Identifier Length Data Item
   (Section 3.1) used to announce the length of Link Identifiers at
   session initialization.

3.1.  Link Identifier Length Data Item

   The Link Identifier Length Data Item MAY be used by a DLEP modem
   implementation to define the length of Link Identifier Data Items if
   it does not with to use the default value of 4 octets.

   The Link Identifier Length Data Item MAY be used during Session
   Initialization, contained in a Session Initialization Response
   Message.

    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                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Link Identifier Length                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBD2, Section 5

   Length:  2

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   Link Identifier Length:  The length, in octets, of Link Identifiers
      used by the DLEP modem for this session.

3.2.  Link Identifier Data Item

   The Link Identifier Data Item MAY be used wherever a MAC Address Data
   Item is defined as usable in core DLEP.

    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:  TBD3, Section 5

   Length:  The length of the Data Item, by default 5, but may be
      different if a Link Identifier Length Data Item (Section 3.1) has
      been announced during session initialization.

   Flags:  Flags field, defined below.

   Link Identifier:  The unique identifier of the Layer 3 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.

4.  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.

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5.  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
      Length".

   o  Assign a new value (TBD3) from the Specification Required section
      of the DLEP Data Item Type Values Registry, named "Link
      Identifier".

5.1.  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 RFC 5226
   defined policies that should apply to the registry:

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

6.  References

6.1.  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, <https://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, <https://www.rfc-
              editor.org/info/rfc8175>.

6.2.  Informative References

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

Authors' Addresses

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

   Email: rick.taylor@airbus.com

   Stan Ratliff
   VT iDirect
   13861 Sunrise Valley Drive, Suite 300
   Herndon, VA  20171
   USA

   Email: sratliff@idirect.net

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