DLEP Multi-Hop Forwarding Extension
draft-ietf-manet-dlep-multi-hop-extension-03

Abstract

This document defines an extension to the DLEP protocol that enables the reporting and control of Multi-Hop Forwarding by DLEP capable modems.

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 May 31, 2018.

Copyright Notice

Copyright (c) 2017 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 Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

Table of Contents

• 1. Introduction
• 1.1. Key Words
• 2. Extension Usage and Identification
• 3. Extension Data Items
• 3.1. Hop Count
• 3.2. Hop Control
• 3.2.1. Reset
• 3.2.2. Terminate
• 3.2.3. Direct Connection
• 3.2.4. Suppress Forwarding
• 4. Security Considerations
• 5. IANA Considerations
• 5.1. Extension Type Value
• 5.2. Data Item Values
• 5.3. Hop Control Actions Registry
• 6. References
• 6.1. Normative References
• 6.2. Informative References
• Appendix A. Acknowledgments
• Authors' Addresses

1. Introduction

The Dynamic Link Event Protocol (DLEP) is defined in [RFC8175]. It provides the exchange of link related control information between DLEP peers. DLEP peers are comprised of a modem and a router. DLEP defines a base set of mechanisms as well as support for possible extensions. This document defines one such extension.

Some modem technologies support connectivity to destinations via multi-hop forwarding. DLEP Destination messages can be used to report such connectivity, see [RFC8175], but do not provide any information related to the number or capacity of the hops. The extension defined in this document enables modems to inform routers when multi-hop forwarding is being used, and routers to request that modems change multi-hop forwarding behavior. The extension defined in this document is referred to as "Multi-Hop Forwarding".

This document defines a new DLEP Extension Type Value in Section 2 which is used to indicate the use of the extension, and three new DLEP Data Items in Section 3.

1.1. Key Words

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

2. Extension Usage and Identification

The use of the Multi-Hop Forwarding Extension SHOULD be configurable. To indicate that the extension is to be used, an implementation MUST include the Multi-Hop Forwarding Extension Type Value in the Extensions Supported Data Item. The Extensions Supported Data Item is sent and processed according to [RFC8175].

The Multi-Hop Forwarding Extension Type Value is TBA1, see Section 5.

3. Extension Data Items

Three data items are defined by this extension. The Hop Count Data Item is used by a modem to provide the number of network hops traversed to reach a particular destination. The Hop Control Data Item is used by a router to request that a modem alter connectivity to a particular destination. The Suppress Forwarding Data Item is used by a router to request that a modem disable multi-hop forwarding on either a device or destination basis.

3.1. Hop Count

The Hop Count Data Item is used by a modem to indicate the number of physical hops between the modem and a specific destination. In other words, each hop represents a transmission and the number of hops is equal to the number of transmissions required to go from a router connected modem to the destination's connected modem. The minimum number of hops is 1, which represents the router's locally connected modem.

The data item also contains an indication of when a destination which currently has a hop count of greater than one (1) could be made direcly reachable by a modem, e.g., by re-aiming an antenna.

The Hop Count Data Item SHOULD be carried in the Destination Up, Destination Update, Destination Announce Response, and Link Characteristics Response Messages when the Hop Count to a destination is greater than one (1).

A router receiving a Hop Count Data Item MAY use this information in its forwarding and routing decisions, and specific use is out of scope of this document. The absence of the Hop Count Data Item MUST be interpreted by the router as a Hop Count value of one (1).

The format of the Hop Count Data Item is:

     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                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |P|  Reserved   |   Hop Count   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Data Item Type:

TBA2

Length:

4

P:

The P-bit indicates that a destination is potentially directly reachable. When the P-bit is set, the router MAY request a direct link to the associated destination using the Hop Control Data Item described below.

Reserved:

MUST be set to zero by the sender (a modem) and ignored by the receiver (a router).

Hop Count:

An unsigned 8-bit integer indicating the number of network hops required (i.e., number of times a packet will be transmitted) to reach the destination indicated in the message. The special value of 255 (0xFF) is used to indicate that the number of hops is an unknown number greater than one (1). This field MUST contain a value of at least one (1) if the associated destination is reachable.

A value of zero (0) is used to indicated that processing of a Hop Control action, see Section 3.2, has resulted in a destination no longer being reachable. A zero value MUST NOT be used in any message other then a Destination Announce Response Message.

3.2. Hop Control

The Hop Control Data Item is used by a router to request a change in connectivity to a particular destination, or in multi-hop processing on a device wide basis. A router can request multi-hop reachable destination be changed to a single hop. A router can also indicate that the modem terminate connectivity to a particular destination.

The Hop Control Data Item MAY be carried in a Session Update Message when the control applies to the whole device, or a Link Characteristics Request Message when the control applies to a particular destination.

A router that receives the Hop Control in a Session Update Message SHOULD attempt to make the change indicated by the data item for the whole device. Results of any changes made are reflected in Destination Down and Destination Update Messages. The modem MUST notify the router of each destination that is no longer reachable via a Destination Down Message. The modem MUST notify the router of any changes in Hop Counts via Destination Update Messages.

A modem that receives the Hop Control Data Item in a Link Characteristics Request Message SHOULD attempt to make the change indicated by the data item for the associated destination MAC address. Once the change is made, or fails or is rejected, the modem MUST respond with a Link Characteristics Request Message containing an updated Hop Count Data Item. Note that other destinations can be impacted as a result of the change and such changes are reported in Destination Down and Destination Update Messages. The modem MUST notify the router of each destination that is no longer reachable via a Destination Down Message. The modem MUST notify the router of any changes in Hop Counts via Destination Update Messages.

A modem that receives the Hop Control Data Item in a Session Update Message SHOULD attempt to make the change indicated by the data item for the associated destination MAC address, when carried in a Link Characteristics Request Message, or all destinations, when carried in a Session Update Message. Once the change is made, or fails or is rejected, the modem MUST respond with a Link Characteristics Request Message containing an updated Hop Count Data Item. Note that other destinations can be impacted as a result of the change and such changes are reported in Destination Down and Destination Update Messages. The modem MUST notify the router of each destination that is no longer reachable via a Destination Down Message. The modem MUST notify the router of any changes in Hop Counts via Destination Update Messages.

The format of the Hop Control Data Item is:

     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                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |       Hop Control Actions     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Data Item Type:

TBA3

Length:

4

Hop Control Actions:

An unsigned 16-bit value with the following meaning:

3.2.1. Reset

The Reset Action requests that the default behavior be restored. When received in a Session Update Message message, a modem SHOULD clear all control actions that have previously been processed on a device wide basis, and revert to its configured behavior. When received in a Link Characteristics Request Message, a modem SHOULD clear all control actions that have previously been processed for the destination indicated in the message.

3.2.2. Terminate

The Terminate Action is only valid on a per destination basis and MUST NOT be sent in a Session Update Message message. It indicates that the modem SHOULD attempt to terminate communication with the destination identified in the message. This request has no impact for multi-hop destinations and may fail even in a single hop case, i.e. MAY result in the Hop Count to the destination not being impacted by the processing of the request

3.2.3. Direct Connection

The Direct Connection is only valid on a per destination basis and MUST NOT be sent in a Session Update Message message. It indicates that the modem SHOULD attempt to establish a direct connection with the destination identified in the message. This action SHOULD only be sent for destinations for which the Hop Count is greater than 1 and has the P-Bit set in the previously received Hop Count Data Item. Results of the request for the destination identified in the message are provided as described above. If any other destination is impacted in the processing of this action, the modem MUST send a Destination Update Message for each impacted destination.

3.2.4. Suppress Forwarding

The Suppress Forwarding Action is used by a router to indicate to its peer that multi-hop forwarding is to be suppressed. A router may request that multi-hop forwarding may be suppressed on a device wide or destination specific basis.

A modem which receives the Suppress Forwarding Data Item in a Session Update Message MUST suppress multi-hop forwarding on a device wide basis. Impact to destination hop counts are provided to the router by the modem as described above.

A modem which receives the Suppress Forwarding Data Item in a Link Characteristics Request Message MUST suppress multi-hop forwarding for only the destination indicated in the message. Results are provided as described above.

4. Security Considerations

The extension enables the reporting and control of forwarding information by DLEP capable modems. The extension does not inherently introduce any additional threats above those documented in [RFC8175]. The approach taken to Security in that document applies equally when running the extension defined in this document.

5. IANA Considerations

This document requests the assignment of 3 values by IANA. All assignments are to registries defined by [RFC8175]. It also requests creation of one new registry.

5.1. Extension Type Value

This document requests 1 new assignment to the DLEP Extensions Registry named "Extension Type Values" in the range with the "Specification Required" policy. The requested value is as follows:

5.2. Data Item Values

This document requests 2 new assignments to the DLEP Data Item Registry named "Data Item Values" in the range with the "Specification Required" policy. The requested values are as follows:

5.3. Hop Control Actions Registry

Upon approval of this document, IANA is requested to create a new DLEP registry, named "Hop Control Actions Values". The following table provides initial registry values and the [RFC8126]. defined policies that should apply to the registry:

6. References

6.1. Normative References

6.2. Informative References

Appendix A. Acknowledgments

Henning Rogge provided valuable input to this work.

Authors' Addresses