Title: LoRa Mesh Details
Description: Meshtastic wire format, channels, and flood routing on GhostESP
URL: /latest/lora/mesh/
Version: latest
Section: LoRa Meshtastic
Keywords: LoRa, Meshtastic, wire format, AES-CTR, LongFast, NodeInfo, flood
Search index: /search-index.json

# LoRa Mesh Details

> Meshtastic wire format, channels, and flood routing on GhostESP

## On this page

- [Wire format](#wire-format)
- [Region and channel](#region-and-channel)
- [Routing](#routing)
- [NodeInfo](#nodeinfo)

---

GhostESP speaks the stock Meshtastic wire format so it interoperates with unmodified firmware.
## Wire format
Each LoRa frame is:
[16 B header] [AES-CTR ciphertext: protobuf Data]
- Header (16 B): from, to, packet ID, flags, channel hash, next hop, and relay node.
- Ciphertext: AES-CTR with the channel PSK (LongFast default PSK AQ== → chash 0x08) covering the serialized Data protobuf (portnum, payload, routing fields).
- De-dup: from + packet ID identifies a message. Repeats may still be acknowledged, but they are not shown twice in chat.
Direct messages use X25519 and authenticated AES-CCM instead of the channel key. Both nodes must first learn each other’s public key from NodeInfo.
## Region and channel
- Region slots: each of the 24 region presets selects a Meshtastic frequency slot, bandwidth, spreading factor, coding rate, and power ceiling (e.g., US LongFast at 906.875 MHz / SF11 / BW250). GhostESP and stock nodes must agree; mismatch = no RX.
- Sync word: 0x442B — Meshtastic private LoRa sync word (not 0x12/0x34 public). GhostESP sets this on SX1262 at lora start; stock nodes ignore frames with other sync words.
- Default-key channel: LongFast on chash 0x08. Custom PSKs derive a different chash; both ends must match.
## Routing
- Flood: relays wait for a short SNR-weighted window. Hearing another copy can cancel an unnecessary transmission.
- Destination: a packet addressed to this node is delivered and acknowledged, not rebroadcast.
- Reliable messages: the sender makes up to three attempts. The delay is calculated from modem airtime; on LongFast it is normally several seconds.
- Next hop: successful ACKs can teach a preferred relay. If that route fails, the final retry falls back to normal flooding.
- Duty guard: regional guard throttles forwarded TX when the band duty budget is exhausted.
## NodeInfo
- Interval: every 3 hours per node (plus on boot and on explicit request). GhostESP sends its long/short name, HW model, and role after lora start.
- Discovery: first 30–60 seconds after lora start populates lora nodes as NodeInfos arrive. Nodes expire from the list only on long silence.
- Diagnostics: lora nodes and lora diag expose last NodeInfo timestamps, SNR/RSSI, and hop counts.
- Capacity: Heltec V3 keeps up to 200 nodes in RAM. Up to 32 important peer records are retained across reboot, prioritizing public keys and user flags.
See [Commands](/latest/lora/commands/) for tuning SF/BW and [Getting Started](/latest/lora/getting-started/) for first contact.