Overview
LDP (Lantronix Discovery Protocol) is a vendor-specific discovery protocol used by Lantronix management tools, such as DeviceInstaller, to locate and identify Lantronix serial-to-Ethernet devices on a local network. It runs over UDP port 30718 (0x77FE) — a de facto Lantronix-assigned port with no corresponding IANA registration — via broadcast queries that devices answer in cleartext.
The discovery response carries a 2-byte numeric device ID at a fixed payload offset (e.g. 58 39 = "X9", identifying an XPort-05), resolved to a product family via Lantronix's Product Information Base (PIB), alongside the device's MAC address embedded at another fixed offset. A separate query/response exchange (opcode 0x000000f4/0x000000f6) returns the device's extended firmware version string in cleartext at a fixed offset — exposing vendor, product family, and firmware version directly from unauthenticated wire fields.
Device Identification
Lantronix devices use predefined device IDs, with each ID corresponding to a specific product family or device type. The mapping of device IDs to product families can be found in the PIB (Product Information Base) file. The following hex dump shows an example request and response exchanged during the device discovery process. In this example, the device ID X9 identifies the device as an XPort-05.
| Filter | Hex | Description |
|---|---|---|
| udp.payload[8:2] | 58 39 | Device ID: X9 |
| udp.payload[24:6] | 00 80 a3 XX XX XX | Mac |
echo -n "000000f6" | xxd -r -p | netcat -u XXX.XXX.XXX.XXX 30718
(00 01 00 f6 seems to do the same)
0000 00 00 00 f6 ....
0000 00 00 00 f7 XX XX XX XX 58 39 XX XX XX XX XX XX ..... ..X90.\...
0010 XX XX XX XX XX XX XX XX 00 80 a3 XX XX XX b...........C.
| Filter | Hex | Description |
|---|---|---|
| udp.payload[16:7] | 36 2e 39 2e 30 2e 32 | Extended Firmware Version 6.9.0.2 |
echo -n "000000f4" | xxd -r -p | netcat -u XXX.XXX.XXX.XXX 30718
0000 00 00 00 f4 ....
0000 00 00 00 f5 XX XX XX XX XX XX XX XX XX XX XX XX ............\...
0010 36 2e 39 2e 30 2e 32 XX XX XX XX XX XX XX XX XX 6.9.0.2.....C...
0020 XX .
Reference
Product Information Base (PIB) Viewer
Lantronix deviceinstaller
resource.zip