Routing & RPL · Study deck

How a DODAG Forms

An RPL root begins by announcing a routing instance, and nearby low-power nodes choose parents before advertising farther outward.

Packet Pete is your guide for this deck.

dodagconstructionrank

Packet Pete, the module guide, in a scene from this chapter.

After studying this chapter

Learning objectives

You will be able to:

Explain: Each node that hears the announcement must decide whether it belongs, how far it is from the root, and which parent makes the graph safer or cheaper to use.
Explain: Node C hears A with link cost 20 and B with link cost 35, so its additive candidates differ by 15 even though parent ranks match.
Explain: HOPS, QUALITY, and LOOP RULE show why the same topology can produce different Rank values while still requiring a parent with lower Rank.
Explain: The deeper sections explain announcements, rank, joining, repair, and the evidence needed to accept the graph.

Major section

Watch the DODAG Grow One Advertisement at a Time

A DODAG can contain several candidate links even though each node selects a preferred parent.

Node C hears A with link cost 20 and B with link cost 35, so its additive candidates differ by 15 even though parent ranks match.
The constraint prevents a node from selecting a parent that is farther down its own directed path.
It selects A and advertises a rank greater than 512 under the configured objective function.

Generic multi-root directed acyclic graph contrasted with a single-root RPL destination-oriented DAG and increasing Rank.

Major section

Start With the Root Announcement

Each device needs a next step, but the strongest neighbour now may fail after rain or battery loss.

The route must change without forming a loop or hiding lost data.
Internet Protocol means the addressing rules used to move network packets.
IPv6 means version 6 of those rules.
A map must show no path when none exists.

Major section

Start With the Root Announcement (continued)

Telemetry is the sensor data travelling upward toward the DODAG root.

Routing Protocol for Low-Power and Lossy Networks (RPL) means rules for choosing paths in such a network.
A directed acyclic graph means one-way paths without a loop back to the start.
This runway does not prove the best parent rule or network scale.

RPL parent selection comparing hop-count and ETX costs, with a blocked-link alternative and the monotonic Rank loop rule.

Major section

Start With the Root Announcement (continued)

A destination-oriented version leads toward one root and is called a DODAG.

The deeper sections explain announcements, rank, joining, repair, and the evidence needed to accept the graph.
A DODAG starts to form when the root announces a graph that other nodes can evaluate.
Each node that hears the announcement must decide whether it belongs, how far it is from the root, and which parent makes the graph safer or cheaper to use.

DODAG construction is a sequence: advertise, evaluate, join, propagate, register reachability, and maintain.

Major section

Practitioner: Record The Parent Decision, Not Just The Final Tree

Its labeled path shows how RPL DODAG Rank Assignment, which makes this section's next operational choice explicit.

The final tree can also hide an asymmetric link.

Major section

Under The Hood: DAO, Trickle, And Repair Are Separate Evidence Layers

The result gives Under The Hood: DAO, Trickle, And Repair Are Separate Evidence Layers an observable meaning.

HOPS, QUALITY, and LOOP RULE show why the same topology can produce different Rank values while still requiring a parent with lower Rank.
Locate “Root” in the The evidence map keeps discovery, parent choice, route state, timing, repair, and packet confirmation as distinct review claims diagram, then ask how “DODAG ID” changes the claim. “DIO” completes the pictured test: the evidence map keeps discovery, parent choice, route state, timing, repair, and packet confirmation as distinct review claims.
DIO advertises the graph while DAO handles downward reach, so neither a tree shape nor Rank alone proves packet delivery.

The evidence map keeps discovery, parent choice, route state, timing, repair, and packet confirmation as distinct review claims.

Deck summary

Key takeaways

A DODAG can contain several candidate links even though each node selects a preferred parent.

Each device needs a next step, but the strongest neighbour now may fail after rain or battery loss.
Telemetry is the sensor data travelling upward toward the DODAG root.
A destination-oriented version leads toward one root and is called a DODAG.
Its labeled path shows how RPL DODAG Rank Assignment, which makes this section's next operational choice explicit.

Retrieval practice

Recall check 1 of 3

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

Q1What is the best overview description of RPL DODAG construction?

ANodes join from signal strength because the strongest neighbor supplies the correct DIO and Rank.

BDAO starts the DODAG, while DIO appears after the graph settles.

CThe root sends DIOs; nodes choose parent and Rank, advertise, and add DAO for downward routes.

DTrickle chooses every route centrally instead of controlling DIO timing.

Show answer

Answer: C RPL DODAG construction should be reviewed as root advertisement, compatible DIO reception, candidate parent and Rank evaluation, onward DIO propagation, optional DAO route state, and maintenance.

Retrieval practice

Recall check 2 of 3

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

Q2A joining node hears Parent A with advertised Rank 256 and local link increase 384, and Parent B with advertised Rank 512 and local link increase 128. What is the safest review conclusion?

AParent A wins because its advertised Rank is lower before link cost.

BParent B wins because its local link increase is smaller.

CBoth candidates are rejected because equal Rank prevents joining.

DBoth parents yield Rank 640; tie and stability policy must decide.

Show answer

Answer: D A practitioner review should calculate candidate Rank from parent Rank plus the local increase, then record the policy or stability evidence used to break ties.

Retrieval practice

Recall check 3 of 3

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

Q3Which review statement keeps RPL construction evidence fail-closed?

AA captured DIO establishes DAO state and packet delivery in both route directions.

BA Trickle reset proves the application is healthy because it increases DIO activity.

CA root-triggered reconstruction and a local parent switch should be recorded as the same repair event.

DTreat DIO discovery, parent choice, DAO state, Trickle timing, repair, and packet delivery as separate claims.

Show answer

Answer: D Under-the-hood review keeps each RPL construction layer tied to the evidence that actually proves it, especially for downward routing and repair behavior.

Print reference

Answers

Answer key.

C · RPL DODAG construction should be reviewed as root advertisement, compatible DIO reception, candidate parent and Rank evaluation, onward DIO propagation, optional DAO route state, and maintenance.
D · A practitioner review should calculate candidate Rank from parent Rank plus the local increase, then record the policy or stability evidence used to break ties.
D · Under-the-hood review keeps each RPL construction layer tied to the evidence that actually proves it, especially for downward routing and repair behavior.