Mobile Ad hoc Networks Working Group R. Taylor
Internet-Draft Airbus Defence & Space
Intended status: Standards Track S. Ratliff
Expires: May 15, 2018 VT iDirect
November 11, 2017
Link Identifier Extension to DLEP
draft-dlep-lid-02
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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This Internet-Draft will expire on May 15, 2018.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements . . . . . . . . . . . . . . . . . . . . . . 3
2. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Identifier Restrictions . . . . . . . . . . . . . . . . . 4
2.2. Negotiation . . . . . . . . . . . . . . . . . . . . . . . 4
3. Link Identifier Data Item . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5.1. DLEP Link Identifier Flag . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . 6
6.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
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
in the network for purposes of reporting the state and quality of the
link to that destination.
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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.
To enable devices to take advantage of the DLEP protocol this
extension adds a single enhancement: A new Link Identifier Data Item
(Section 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 refer to a Layer 3 DLEP Destination, the DLEP session participant
adds a Link Identifier Data Item (Section 3) 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 4 octets in length. 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
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
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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. 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: TBD2, Section 5
Length: 5
Flags: Flags field, defined below.
Link Identifier: The 4 octet 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".
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
[RFC5226] 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
[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>.
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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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