--- 1/draft-ietf-roll-turnon-rfc8138-03.txt 2020-01-24 09:13:14.954606191 -0800 +++ 2/draft-ietf-roll-turnon-rfc8138-04.txt 2020-01-24 09:13:14.978606887 -0800 @@ -1,19 +1,19 @@ ROLL P. Thubert, Ed. Internet-Draft L. Zhao Updates: 6550, 8138 (if approved) Cisco Systems -Intended status: Standards Track 22 January 2020 -Expires: 25 July 2020 +Intended status: Standards Track 24 January 2020 +Expires: 27 July 2020 Configuration option for RFC 8138 - draft-ietf-roll-turnon-rfc8138-03 + draft-ietf-roll-turnon-rfc8138-04 Abstract This document complements RFC 8138 and dedicates a bit in the RPL configuration option defined in RFC 6550 to indicate whether RFC 8138 compression is used within the RPL Instance. Status of This Memo This Internet-Draft is submitted in full conformance with the @@ -22,166 +22,174 @@ 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/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any 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 25 July 2020. + This Internet-Draft will expire on 27 July 2020. Copyright Notice Copyright (c) 2020 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 . . . . . . . . . . . . . . . . . . . . . . . . 2 2. BCP 14 . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 - 3. Updating RFC 6550 . . . . . . . . . . . . . . . . . . . . . . 2 + 3. Updating RFC 6550 . . . . . . . . . . . . . . . . . . . . . . 3 4. Updating RFC 8138 . . . . . . . . . . . . . . . . . . . . . . 3 - 5. Transition Scenarios . . . . . . . . . . . . . . . . . . . . 3 + 5. Transition Scenarios . . . . . . . . . . . . . . . . . . . . 4 5.1. Inconsistent State While Migrating . . . . . . . . . . . 5 5.2. Single RPL Instance Scenario . . . . . . . . . . . . . . 5 5.3. Double RPL Instances Scenario . . . . . . . . . . . . . . 6 5.4. Rolling Back . . . . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7 9. Normative References . . . . . . . . . . . . . . . . . . . . 7 10. Informative References . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction - The transition to [RFC8138] in a network can only be done when all - nodes support the specification. In a mixed case with both - RFC8138-capable and non-capable nodes, the compression should be - turned off. + The transition of a RPL [RFC6550] network to activate the compression + defined in [RFC8138] can only be done when all routers in the network + support it. A non-capable node acting as a router would drop the + compressed packets and black-hole its subDAG. In a mixed case with + both RFC8138-capable and non-capable nodes, the compression may be + turned on only if all the non-capable nodes act as leaves and their + RPL parents handle the compression/decompression on their behalf. - This document complements RFC 8138 and dedicates a bit in the RPL + This document complements RFC 8138 and dedicates a flag in the RPL configuration option to indicate whether RFC 8138 compression should - be used within the RPL Instance. When the bit is not set, source - nodes that support RFC 8138 should refrain from using the compression - unless the information is superseded by configuration. + be used within the RPL Instance. The setting of new flag is + controlled by the Root and propagates as is in the whole network. + When the bit is not set, source nodes that support RFC 8138 should + refrain from using the compression unless the information is + superseded by configuration. + + This specification provides scenarios that force a legacy node to + become a RPL-Aware-Leaf (RAL). In that case, the 6LR must be aware + by means out of scope that it must uncompress the packets before + delivering to the RAL. 2. BCP 14 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. 3. Updating RFC 6550 - RPL defines a configuration option that is registered to IANA in - section 20.14. of [RFC6550]. This specification defines a new flag - "Enable RFC8138 Compression" (T) that is encoded in one of the - reserved control bits in the option. The new flag is set to turn on - the use of the compression of RPL artifacts with RFC 8138. The bit + This specification defines a new flag "Enable RFC8138 Compression" + (T). The "T" flag is set to turn on the use of the compression of + RPL artifacts with [RFC8138] within a RPL Instance. If a RPL + Instance has multiple Roots then they must be coordinated to use the + same setting. + + RPL defines a Configuration Option that is registered to IANA in + section 20.14. of [RFC6550]. The "T" flag is encoded in one of the + reserved control bits in the RPL Configuration Option. The bit position of the "T" flag is indicated in Section 6. Section 6.3.1. of [RFC6550] defines a 3-bit Mode of Operation (MOP) in the DIO Base Object. The new "T" flag is defined only for MOP value between 0 to 6. For a MOP value of 7 or above, the flag MAY indicate something different and MUST NOT be interpreted as "Enable RFC8138 Compression" unless the specification of the MOP indicates to do so. 4. Updating RFC 8138 - This document specifies controls that enable and disable the use of - the [RFC8138] compression in a RPL Instance. Arguably, this could - have been done in [RFC8138] itself. - - A node that supports this specification SHOULD source packets in the - compressed form using [RFC8138] if the new "T" flag is set in the RPL - configuration option from its parents. Failure to do so will result - in larger packets, yields higher risks of loss and may cause a - fragmentation. + A node that supports this specification MUST source packets in the + compressed form using [RFC8138] if and only if the "T" flag is set. + This behaviour can be overridden by a configuration of the node in + order to cope with intermediate implementations of the root that + support [RFC8138] but not this specification and cannot set the "T" + flag. - A node that supports this specification SHOULD refrain from sourcing - packets in the compressed form using [RFC8138] if the "T" flag is - reset. This behaviour can be overridden by a configuration of the - node in order to cope with intermediate implementations of the root - that support [RFC8138] but not this specification and cannot set the - "T" flag. + The decision of using [RFC8138] is made by the originator of the + packet depending on its capabilities and its knowledge of the state + of the "T" flag. A router that encapsulates a packet is the + originator of the resulting packet and decides whether to compress + the outer headers as indicated above. An external target + [USEofRPLinfo] is not expected to support [RFC8138]. An intermediate + router MUST forward the packet in the form that the source used, + either compressed or uncompressed, unless it is either forwarding to + an external target or delivering to a leaf that is not known to + support RFC 8138, in which cases it MUST uncompress the packet. - The decision of using RFC 8138 to compress a packet is made at the - source depending on its capabilities and its knowledge of the state - of the "T" flag. A router MUST forward the packet in the form that - the source used, either compressed or uncompressed. A router that - encapsulates a packet is the source of the resulting packet and the - rules above apply to it in that case. + A RPL-Unaware Leaf (RUL) [UNAWARE-LEAVES] is both a leaf and an + external target. A RUL does not participate to RPL and depends on + the 6LR to ensure its connectivity. Packets from/to a RUL are + tunneled back and forth to the Root regardless of the MOP used in the + RPL Instance. A node that supports this specification but does not + support [RFC8138] SHOULD join as a RUL to ensure that the 6LR is + aware it needs to uncompress the packets before delivering. 5. Transition Scenarios A node that supports [RFC8138] but not this specification can only be used in a homogeneous network and an upgrade requires a "flag day" where all nodes are updated and then the network is rebooted with implicitly RFC 8138 compression turned on with the "T" flag set on. A node that supports this specification can work in a network with RFC 8138 compression turned on or off with the "T" flag set accordingly and in a network in transition from off to on or on to off (see Section 5.1). - A node that does not support [RFC8138] can interoperate with a node - that supports this specification in a network with RFC 8138 - compression turned off. But it cannot forward compressed packets and - therefore it cannot act as a router in a network with RFC 8138 - compression turned on. It may remain connected to that network as a - leaf and generate uncompressed packets. The leaf can receive packets - if they are delivered by the parent 6LR in the uncompressed form. - This requires a knowledge by the 6LR that the leaf does not support - RFC 8138. A RPL-Unaware-Leaf (RUL) [USEofRPLinfo] is an external - target and by default is not expected to support RFC 8138. + A node that does not support [RFC8138] can interoperate with nodes + that do in a network with RFC 8138 compression turned off. If the + compression is turned on, the node cannot forward compressed packets + and therefore it cannot act as a router. It may remain connected to + that network as a leaf, in which case it generates uncompressed + packets and can receive packets if they are delivered by the parent + 6LR in the uncompressed form. [RFC6550] states that "Nodes other than the DODAG root MUST NOT modify this information when propagating the DODAG Configuration - option". In other words, the configuration option is a way for the - root to configure the LLN nodes but it cannot be used by a parent to - advertise its capabilities down the DODAG. A parent propagates the - "T" flag as set whether it supports RFC 8138 or not. The setting of - the "T" flag can thus not be used as an indication of the support by - the sender, and a child cannot favor a parent based on it. + option". Therefore, even a legacy parent propagates the "T" flag as + set by the Root whether it supports this specification or not. So + when the "T" flag is set, it is transparently flooded to all the + nodes in the RPL Instance. Sections 8.5 and 9.2 of [RFC6550] also suggests that a RPL-aware node - may attach to a DODAG as a leaf node only, e.g., when a node does not + may only attach to a DODAG as a leaf node when the node does not support the Mode of Operation of a RPL Instance, the Objective Function (OF) as indicated by the Objective Code Point (OCP) or some - other parameters in the configuration option. [USEofRPLinfo] - indicates that the node may also join as a RUL, in which case it - refrains from participating to RPL and depends on the 6LR to ensure - connectivity regardless on the way the RPL network is operated. + other parameters in the configuration option. - This means that changing the OCP in a DODAG can be used to force - nodes that do not support a particular feature to join as leaf only. - This specification reiterates that a node that is configured to - operate in a RPL Instance but does not support a value for a known - parameter that is mandatory for routing MUST NOT operate as a router - but MAY still join as a leaf. Note that a legacy node will not - recognize when a reserved field is now used and will not turn to a - leaf when that happens. + Per the above, changing the OCP in a DODAG can be used to force nodes + that do not support a particular feature to join as leaf only. This + specification reiterates that a node that is configured to operate in + a RPL Instance but does not support a value for a known parameter + that is mandatory for routing MUST NOT operate as a router but MAY + still join as a leaf. Note that a legacy node will not recognize + when a reserved field is now used and will not turn to a leaf when + the "T" flag is set. The intent for this specification is to perform a migration once and for all without the need for a flag day. In particular it is not the intention to undo the setting of the "T" flag, and though it is possible to roll back (see Section 5.4), adding nodes that do not support [RFC8138] after a roll back may be problematic if the roll back is not fully complete (see caveats in Section 5.2). 5.1. Inconsistent State While Migrating @@ -276,36 +284,39 @@ +------------+---------------------------------+-----------+ | Bit Number | Capability Description | Reference | +============+=================================+===========+ | 2 | Turn on RFC8138 Compression (T) | THIS RFC | +------------+---------------------------------+-----------+ Table 1: New DODAG Configuration Option Flag 7. Security Considerations - Turning the "T" flag on before some routers are upgraded may cause a + Setting the "T" flag before some routers are upgraded may cause a loss of packets. The new bit is protected as the rest of the configuration so this is just one of the many attacks that can happen if an attacker manages to inject a corrupted configuration. - Turning the "T" flag on and off may create inconsistencies in the + Setting and resetting the "T" flag may create inconsistencies in the network but as long as all nodes are upgraded to RFC 8138 support they will be able to forward both forms. The draft insists that the source is responsible for selecting whether the packet is compressed or not, and all routers must use the format that the source selected. So the result of an inconsistency is merely that both forms will be present in the network, at an additional cost of bandwidth for packets in the uncompressed form. 8. Acknowledgments + The authors wish to thank Rahul Jadhav for his in-depth review and + constructive suggestions. + 9. 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, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . @@ -318,20 +329,26 @@ . [USEofRPLinfo] Robles, I., Richardson, M., and P. Thubert, "Using RPI Option Type, Routing Header for Source Routes and IPv6-in- IPv6 encapsulation in the RPL Data Plane", Work in Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-34, 20 January 2020, . + [UNAWARE-LEAVES] + Thubert, P. and M. Richardson, "Routing for RPL Leaves", + Work in Progress, Internet-Draft, draft-ietf-roll-unaware- + leaves-08, 16 December 2019, . + 10. Informative References [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, "IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, April 2017, . [MOP-EXT] Jadhav, R., Thubert, P., and M. Richardson, "Mode of Operation extension and Capabilities", Work in Progress, Internet-Draft, draft-ietf-roll-mopex-cap-01, 2 November