Routing & RPL · Study deck

The RPL Standard (RFC 6550)

A building sensor's product sheet lists support for the RPL standard.

Packet Pete is your guide for this deck.

rfc-6550ipv6dodag
Packet Pete, the module guide, in a scene from this chapter.
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After studying this chapter

Learning objectives

You will be able to:

  • check the RPL protocol pieces (messages, modes, headers) in the order RFC 6550 defines them
  • treat RFC 6550 as the contract that RPL implementations must satisfy
  • map RPL messages and modes onto their specification sections
  • Explain: Lower link quality, remove the parent, restart the root, join a second graph, send a downward command, and inject old control state.
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Major section

Start With the Contract

Lower link quality, remove the parent, restart the root, join a second graph, send a downward command, and inject old control state.

  • A formed graph or a product label does not prove the needed packet path.
  • This opening does not restate the full standard or certify a stack.
  • Under the Hood examines graph rules, control objects, rank, parent choice, downward modes, headers, and recovery limits.
RPL builds and maintains the DODAG with three control messages: DIO advertises, DIS solicits, and DAO reports reachability upward.
RPL builds and maintains the DODAG with three control messages: DIO advertises, DIS solicits, and DAO reports reachability upward.
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Major section

Overview: RFC 6550 Defines the RPL Contract

A design citing RFC 6550 should also identify the related rule that governs the claimed metric or route mode.

  • The RFC map identifies the governing rules; observed control messages and forwarding results must establish whether this deployment follows them.
  • That evidence resolves the question posed by Overview: RFC 6550 Defines the RPL Contract.
  • In the RFC 6550 is the base document, with companion RFCs defining metrics, Objective Functions, Trickle behavior, and packet headers diagram, the visual shows rFC 6550 connected to related RFCs for metrics, Objective Functions, Trickle, packet information, and source routing.
RFC 6550 is the base document, with companion RFCs defining metrics, Objective Functions, Trickle behavior, and packet headers.
RFC 6550 is the base document, with companion RFCs defining metrics, Objective Functions, Trickle behavior, and packet headers.
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Major section

Practitioner: Check the Protocol Pieces in Order

DIOs carry the DODAG ID, version, and Rank; the DODAG Configuration option identifies the Objective Function used to compute Rank.

  • The zero-based teaching offsets must not be mistaken for an advertised root Rank; the default actual root value is 256.
  • The DIO and Rank fields in the Rank must preserve the graph direction: upward forwarding moves toward lower Rank and the DODAG root diagram show what a joining node can learn before selecting a parent.
Rank must preserve the graph direction: upward forwarding moves toward lower Rank and the DODAG root.
Rank must preserve the graph direction: upward forwarding moves toward lower Rank and the DODAG root.
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Major section

Turn a Support Claim into an Upward-and-Downward Test

These observations show how the claimed standard is being used; a diagram drawn after the test cannot replace the actual control messages.

  • If all readings arrive but only 3 commands do, the two delivery proportions are 20 divided by 20 = 100% and 3 divided by 5 = 60%.
  • A combined 23 out of 25, or 92%, conceals which direction is weak, and none of these small-sample proportions constitutes standard certification.
  • The standard review should then repeat the command after removing the chosen parent, keeping the fault time and new route state beside the packet capture.
RFC 6550 is the base document, with companion RFCs defining metrics, Objective Functions, Trickle behavior, and packet headers.
RFC 6550 is the base document, with companion RFCs defining metrics, Objective Functions, Trickle behavior, and packet headers.
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Major section

Summary

RFC 6550 defines the base RPL protocol for constrained IPv6 routing in low-power and lossy networks.

  • An RPL Instance gives the routing context, while a DODAG organizes routers around a root.
  • DIO, DIS, DAO, and DAO-ACK are the main RPL control messages to understand before interpreting route state.
  • Storing and Non-Storing modes differ mainly in where downward route state lives and how downward packets are carried.
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Deck summary

Key takeaways

Lower link quality, remove the parent, restart the root, join a second graph, send a downward command, and inject old control state.

  • A design citing RFC 6550 should also identify the related rule that governs the claimed metric or route mode.
  • DIOs carry the DODAG ID, version, and Rank; the DODAG Configuration option identifies the Objective Function used to compute Rank.
  • These observations show how the claimed standard is being used; a diagram drawn after the test cannot replace the actual control messages.
  • RFC 6550 defines the base RPL protocol for constrained IPv6 routing in low-power and lossy networks.
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Retrieval practice

Recall check 1 of 3

Packet Pete says: answer from memory, then check your reasoning.

Q1Which statement best describes the role of RFC 6550 in an RPL deployment?

AIt defines base RPL objects, messages, modes, and packet-processing rules.
BIt requires every RPL network to use the same Objective Function and metric.
CIt replaces IPv6 routing headers with application-layer destination fields.
DIt guarantees that all downward routes are stored on every constrained router.
Show answer

Answer: A RFC 6550 is the base RPL specification.

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Retrieval practice

Recall check 2 of 3

Packet Pete says: answer from memory, then check your reasoning.

Q2A joined RPL node needs to choose a preferred parent for upward traffic. Which check should come before accepting the parent choice?

AVerify the parent fits the instance and preserves movement toward lower Rank.
BPrefer the neighbor with the highest Rank because it is farthest from congestion at the root.
CIgnore the Objective Function once a DIO message has been received.
DSelect only the DODAG root, because intermediate routers cannot be parents.
Show answer

Answer: A Parent selection must be interpreted inside the RPL Instance and must preserve the DODAG direction toward the root.

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Retrieval practice

Recall check 3 of 3

Packet Pete says: answer from memory, then check your reasoning.

Q3In a Non-Storing RPL design, where is downward route state primarily held for source-routed delivery?

AAt the DODAG root, using source routing for downward packets inside the RPL domain.
BOn every leaf device, which rewrites the route for packets sent by the root.
COnly in DAO-ACK messages, which replace routing tables during data forwarding.
DIn application payload fields, because RPL does not use IPv6 packet headers.
Show answer

Answer: A Non-Storing mode concentrates downward route state at the root and uses source routing for downward delivery.

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Print reference

Answers

Answer key.

  1. A · RFC 6550 is the base RPL specification.
  2. A · Parent selection must be interpreted inside the RPL Instance and must preserve the DODAG direction toward the root.
  3. A · Non-Storing mode concentrates downward route state at the root and uses source routing for downward delivery.
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