A node that supports [RFC 8138
] but not this specification can only be used in a homogeneous network. Enabling compression per [RFC 8138
] without a turn-on signaling method requires a flag day, by which time all nodes must be upgraded and at which point the network can be rebooted with 6LoRH compression [RFC 8138
] turned on.
The intent of this specification is to perform a migration once and for all, without the need for a flag day. In particular, the intent is not to undo the setting of the 'T' flag. Though it is possible to roll back (see Section 5.3
), the rollback operation SHOULD
be complete before the network operator adds nodes that do not support [RFC 8138
A node that supports this specification can operate in a network with 6LoRH compression [RFC 8138
] 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 5.2
A node that does not support [RFC 8138
] can interoperate with nodes that do in a network with 6LoRH compression [RFC 8138
] turned off. If compression is turned on, all the RANs are expected to be able to handle packets in compressed form. A node that cannot do so may remain connected to the network as a RUL as described in [RFC 9010
When the 'T' flag is turned on by the Root, the information slowly percolates through the DODAG as the DIO gets propagated. Some nodes will see the flag and start sourcing packets in compressed form, while other nodes in the same RPL DODAG will still not be aware of it. In Non-Storing mode, the Root will start using [RFC 8138
] with a Source Routing Header 6LoRH (SRH-6LoRH) that routes all the way to the parent router or to the leaf.
To ensure that a packet is forwarded across the RPL DODAG in the form in which it was generated, it is required that all the RPL nodes support [RFC 8138
] at the time of the switch.
Setting the 'T' flag is ultimately the responsibility of the network administrator. The expectation is that the network management or upgrading tools in place enable the network administrator to know when all the nodes that may join a DODAG were migrated. In the case of a RPL Instance with multiple Roots, all nodes that participate in the RPL Instance may potentially join any DODAG. The network MUST
be operated with the 'T' flag unset until all nodes in the RPL Instance are upgraded to support this specification.
When turning 6LoRH compression [RFC 8138
] off in the network, the network administrator MUST
wait until each node has its 'T' flag unset before allowing nodes that do not support compression in the network. Information regarding whether compression is active in a node SHOULD
be exposed in the node's management interface.
Nodes that do not support [RFC 8138
] SHOULD NOT
be deployed in a network where compression is turned on. If that is done, the node can only operate as a RUL.