The IETF has developed the IPv6 based standards for Low-power and
Lossy Networks (LLNs) to meet requirements of constrained
applications, such as field monitoring, inventory control and so on.
The IPv6 Routing Protocol for LLNs (RPL) was published as [RFC6550]
in March 2012. Based on routing metrics and constraints [RFC6551],
RPL builds Directed Acyclic Graph (DAG) topology to establish
bidirectional routes for LLNs for traffic types of multipoint-to-
point, point-to-multipoint, and point-to-point. RPL routes are
optimized for traffic to or from one or more roots that act as sinks.
As a result, a DAG is partitioned into one or more Destination
Oriented DAGs (DODAGs), one DODAG per sink. RPL is widely considered
as a feasible routing protocol for LLNs. However, DODAG loops and
lack of a loop free DODAG local repair mechanism are two open issues
to be addressed. This draft introduces an alternative rank and an
Objective Function to eliminate DODAG loops in RPL. Based on the
proposed rank and Objective Function, this draft introduces a loop
free RPL.
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