Mobile Ad hoc Networks Working Group R. Taylor
Internet-Draft Airbus Defence & Space
Intended status: Standards Track S. Ratliff
Expires: February 24, 2019 VT iDirect
August 23, 2018
DLEP Link Identifier Extension
draft-ietf-manet-dlep-lid-extension-04
Abstract
There exists a class of modems that would benefit from supporting 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 remote DLEP destinations do exist, but are not
directly reachable by MAC address, such as modems that contain
embedded routing functionality.
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 https://datatracker.ietf.org/drafts/current/.
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This Internet-Draft will expire on February 24, 2019.
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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 . . . . . . . . . . . . . . . . . . . . . . . 5
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
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Normative References . . . . . . . . . . . . . . . . . . 7
6.2. Informative References . . . . . . . . . . . . . . . . . 7
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
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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 MUST contain the MAC address of the last reachable node in the
Layer 2 domain beyond which the Layer 3 DLEP Destination resides.
For example, if the over-the-air network is not a single Layer 2
domain, the MAC Address Data Item might be the address of the LAN-
side interface of the local modem. Alternatively, when used with
some kind of backbone infrastructure, the MAC Address Data Item would
be the address of the last device reachable on the local Layer 2
domain. However, 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 if it wishes to use
the modem network to forward the packet.
As most mainstream routers expect to populate their routing
information base with the IP address of the next router towards a
destination, implementations supporting this extension SHOULD
announce one or more valid IPv4 or IPv6 addresses of the last
reachable Layer 2 device, i.e. the device with the corresponding MAC
Address.
If the last reachable Layer 2 device is not the DLEP peer modem, then
the modem SHOULD announce a DLEP Destination with the required MAC
Address without including a Link Identifier Data Item.
2.1. Identifier Restrictions
A Link Identifier is by default 4 octets in length. If a modem
wishes to use a Link 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 differ between destinations.
The method for generating Link Identifiers is a modem implementation
matter and out of scope of this document. Routers MUST NOT make any
assumptions about the meaning of Link Identifiers, or how Link
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 Identifier}.
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Link Identifiers MUST NOT be reused, i.e. a {MAC Address,Link
Identifier} pair that has been used to refer to one DLEP 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
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 is used by a DLEP modem
implementation to specify the length of Link Identifier Data Items.
It MUST be used if the specified length is not 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.
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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
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Identifier... :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Data Item Type: TBD3, Section 5
Length: The length of the Data Item, by default 4, but may be
different if a Link Identifier Length Data Item (Section 3.1) has
been announced during session initialization.
Link Identifier: The unique identifier of the Layer 3 destination.
This Link Identifier has no implicit meaning and is only used to
discriminate between multiple links.
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 DLEP Extensions Registry value (TBD1) from the
Specification Required section, named "Link Identifiers".
o Assign a new DLEP Data Item Type Values Registry value (TBD2) from
the Specification Required section, named "Link Identifier
Length".
o Assign a new DLEP Data Item Type Values Registry value (TBD3) from
the Specification Required section, named "Link Identifier".
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>.
Authors' Addresses
Rick Taylor
Airbus Defence & Space
Quadrant House
Celtic Springs
Coedkernew
Newport NP10 8FZ
UK
Email: rick.taylor@airbus.com
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Stan Ratliff
VT iDirect
13861 Sunrise Valley Drive, Suite 300
Herndon, VA 20171
USA
Email: sratliff@idirect.net
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