RPL DODAG Construction

Build an RPL DODAG step by step and see how DIO, rank, parent choice, and DAO messages fit together

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rpl
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intermediate
A guided RPL DODAG workbench for independent learners exploring low-power and lossy IPv6 routing.
RPL routing DODAG construction Low-power IPv6

Watch an RPL network form a loop-free DODAG toward a border router.

Step through the root announcement, DIO propagation, rank calculation, preferred-parent selection, DAO route advertisement, and repair diagnosis used by constrained IoT networks.

Root startsCurrent construction phase
1 / 10Nodes joined to the DODAG
OF0 lensParent selection model
BR onlySelected upward route focus

What is RPL?

RPL is an IPv6 routing protocol for low-power and lossy networks where radios sleep, links vary, and devices have limited memory.

What is a DODAG?

A Destination-Oriented Directed Acyclic Graph is a directed routing structure rooted at one destination, usually a border router.

Why rank matters

Rank is a scalar position relative to the root. Nodes normally choose parents with lower rank, which helps prevent loops.

What moves here?

Blue DIO messages flow outward so nodes can join. Amber DAO messages flow upward to advertise routes back toward the root.

Interactive DODAG map

The border router creates a DODAG version and starts with the lowest rank.

Root Joined node Not joined yet DIO or DAO message

Parent-choice evidence

Node F will compare candidate parents after DIO messages reach it.

Parent Evidence Decision
Rank evidence appears after the focused node can hear joined neighbors.

Loop guard

WaitingParent must be closer to the root in this teaching model.

Repair clue

No faultWatch what changes when a selected link is unavailable.

Message story

DIO

DODAG Information Object. Advertises DODAG identity, version, rank, objective code point, and configuration so neighbors can decide whether to join.

DIS

DODAG Information Solicitation. A node can ask nearby routers for DODAG information instead of waiting for the next multicast DIO.

DAO

Destination Advertisement Object. Sends reachability information upward so downward routes can be maintained when the selected mode uses them.

Rank

A scalar position relative to the DODAG root. Exact calculation depends on the objective function and configured parameters.

Trace formation

  1. Reset to the stable scenario.
  2. Step until first-hop nodes join.
  3. Explain why A, B, and C can advertise DIO next.

Compare objectives

  1. Inspect Node F.
  2. Switch between the OF0 and ETX lenses.
  3. Find the parent-choice evidence that changes.

Diagnose repair

  1. Choose the parent failure scenario.
  2. Watch the broken link mark.
  3. Identify the alternate lower-rank parent.
Technical accuracy notes

Teaching model

This page uses small classroom formulas so learners can see decisions. Real RPL rank is defined by RFC 6550 and shaped by the objective function, MinHopRankIncrease, metrics, and implementation policy.

Objective functions

OF0 is a basic objective function. MRHOF-style behavior prefers a minimum path cost with hysteresis. The ETX lens here is an explanatory model, not a full MRHOF implementation.

Downward routes

DIO helps nodes discover the DODAG. DAO is used to advertise destination reachability upward when the selected RPL mode maintains downward routes.

Primary sources and further reading
6LoWPAN routingContrast mesh-under and route-over forwarding choices. Thread DODAGCompare generic RPL ideas with Thread-specific routing behavior. Mesh topologyReview how multi-hop paths differ from a single preferred-parent tree.