Meshtastic MeshPacket & Data Field Reference: The On-Air Packet Envelope

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The on-air packet envelope for Meshtastic, sourced verbatim from meshtastic/protobufs → mesh.proto (MeshPacket + Data, as of 2026-07-21). Field numbers and types are exact. Routing and crypto behaviour is intentionally left to the linked deep-dives rather than restated here; no RF/frequency/power values appear on a protobuf reference.

Message	Group	Field	#	Type	Purpose
MeshPacket	Addressing	from	1	fixed32	The sending node number. The crypto implementation also uses this field.
MeshPacket	Addressing	to	2	fixed32	The immediate destination. 4,294,967,295 (max uint32) means the packet is a broadcast on the channel; any other value is a direct message to that specific node.
MeshPacket	Addressing	channel	3	uint32	Index into the secondary-channels table the packet was sent/received on; unset means the primary channel. Deep inside the router (while the payload is encrypted) this field instead holds the channel hash. It is a local concept, meaningless to send between nodes.
MeshPacket	Addressing	id	6	fixed32	A unique ID for this packet, used by the flooding algorithm. Always 0 for no-ack or non-broadcast packets; otherwise unique on a per-sender basis.
MeshPacket	Payload (oneof)	decoded	4	Data	The decoded payload (a Data sub-message). Present only once a node with the correct key has decrypted the packet — software outside the mesh radios only ever sees this form.
MeshPacket	Payload (oneof)	encrypted	5	bytes	The encrypted payload bytes, as the packet travels over the air before decryption.
MeshPacket	Routing	hop_limit	9	uint32	Hops remaining before the packet is dropped — decrements at each relay (managed-flood routing).
MeshPacket	Routing	want_ack	10	bool	Request that the destination return an acknowledgement for this packet.
MeshPacket	Routing	priority	11	Priority	Transmit-queue priority (UNSET/MIN/BACKGROUND/DEFAULT/RELIABLE/RESPONSE/HIGH/ALERT/ACK/MAX). Internal only — never sent over the air; it orders the local priority queue so acks and routing go out before background traffic.
MeshPacket	Routing	via_mqtt	14	bool	Set when the packet arrived (or is going) via an MQTT connection rather than the LoRa radio.
MeshPacket	Routing	hop_start	15	uint32	The original hop_limit at send time, so a receiver can compute how many hops the packet actually took.
MeshPacket	Routing	next_hop	18	uint32	The next-hop node (last byte of the node number) used by next-hop routing.
MeshPacket	Routing	relay_node	19	uint32	The relay node (last byte of the node number) that forwarded this packet.
MeshPacket	Routing	tx_after	20	uint32	Requests that the node delay transmission of this packet by this many seconds.
MeshPacket	Routing	transport_mechanism	21	TransportMechanism	Which transport the packet arrived over: INTERNAL, LORA (+ALT1/ALT2/ALT3), MQTT, MULTICAST_UDP, API or UNICAST_UDP.
MeshPacket	Crypto	public_key	16	bytes	The sender public key, used for PKC (public-key) encrypted direct messages.
MeshPacket	Crypto	pki_encrypted	17	bool	True when the packet was encrypted with PKC (per-node public-key) rather than a shared channel PSK.
MeshPacket	Crypto	xeddsa_signed	22	bool	True when the packet carries an XEdDSA signature.
MeshPacket	Receive metadata	rx_time	7	fixed32	The timestamp (seconds) at which the packet was received.
MeshPacket	Receive metadata	rx_snr	8	float	The measured signal-to-noise ratio of the received packet.
MeshPacket	Receive metadata	rx_rssi	12	int32	The measured received signal strength (RSSI) of the packet, in dBm.
Data	Data payload	portnum	1	PortNum	Which application the payload is for — the PortNum enum (see the PortNum registry). Formerly named "typ".
Data	Data payload	payload	2	bytes	The application payload bytes.
Data	Data payload	want_response	3	bool	Ask the recipient to respond in kind (e.g. reply with its own position). On a broadcast this yields many replies.
Data	Data payload	dest	4	fixed32	The destination node address, filled in by the mesh radio software; RouteDiscovery and multihop-routing messages populate it.
Data	Data payload	source	5	fixed32	The original sender address, populated only for reliable multihop packets (to keep packets small).
Data	Data payload	request_id	6	fixed32	The original message ID this message reports failure/response on (routing or response messages). Formerly original_id.
Data	Data payload	reply_id	7	fixed32	If set, this message is a reply to a previously sent message with this ID.
Data	Data payload	emoji	8	fixed32	When set, the payload should be treated as an emoji reaction (e.g. a heart or thumbs-up) to a message.
Data	Data payload	bitfield	9	uint32 (optional)	Bitfield of extra flags; the first use indicates the user approves uploading this packet to MQTT.
Data	Data payload	xeddsa_signature	10	bytes	The XEdDSA signature over the payload.

How the packet fits together

• Addressing — from/to are node numbers; a to of 4,294,967,295 is a channel broadcast, anything else a direct message. id makes each packet unique for the flooding algorithm.
• Payload — over the air the payload is encrypted bytes; a node with the right channel PSK or PKC key decrypts it into the decoded Data sub-message, which apps actually read.
• Routing — hop_limit counts down at each relay (managed-flood routing); hop_start lets a receiver tell how many hops were used; next_hop/relay_node support next-hop routing.
• Crypto — pki_encrypted + public_key mark public-key (PKC) direct messages; details on the encryption page.
• Receive metadata — rx_snr and rx_rssi (dBm) are set locally when a node hears the packet; they never travel over the air.

Related

Meshtastic PortNum registry (this envelope’s portnum field) · encryption & PSK/PKC model · LoRa regional settings · Nostr event-kinds reference (the Nostr analogue).

Credit: the MeshPacket and Data messages are defined and maintained by the Meshtastic project in meshtastic/protobufs (GPL-3.0). This page is a dated, human- and machine-readable index of that file.