NETMODE

NETMODE is a network mode controller for Lichee-Jack, designed to manage the primary Ethernet interface end0 using NetworkManager.

It provides a unified command-line interface to switch between DHCP client, DHCP server, static IP, and an AUTO detection mode that infers network behavior by passively sniffing DHCP traffic.

Features

Switch end0 between common network roles
Integrates cleanly with NetworkManager (nmcli)
Optional embedded DHCP server using udhcpd
Passive AUTO mode using DHCP traffic inspection
Script-friendly and deterministic
LED feedback for AUTO decision results

Dependencies

NetworkManager
nmcli
tcpdump
udhcpd (controlled via UDHCPCTL)
LED utility (optional, for visual feedback)

All dependencies are included in the Lichee-Jack system image.

Supported Modes

Mode	Description
`DHCP_CLIENT`	Bring up DHCP client connection on `end0`
`DHCP_SERVER`	Bring up DHCP server connection and start `udhcpd`
`STATIC`	Bring up static IP connection
`AUTO`	Sniff network traffic and decide client or server
`STOP_ALL`	Deactivate all active connections on `end0`
`<custom>`	Bring up a named NetworkManager connection

Usage


NETMODE <MODE>

Examples:


NETMODE DHCP_CLIENT
NETMODE DHCP_SERVER
NETMODE STATIC
NETMODE AUTO
NETMODE STOP_ALL
NETMODE my-custom-conn

AUTO Mode Logic

AUTO mode performs passive DHCP inspection on end0 for up to 15 seconds:


Listen for:
  UDP src port 68 → dst port 67

Decision Rules

No DHCP traffic detected → fallback to DHCP_CLIENT
DHCP Discover without Request → assume no DHCP server → DHCP_SERVER
DHCP Request detected → DHCP server exists → DHCP_CLIENT

This allows Lichee-Jack to adapt automatically when plugged into:

An unmanaged switch
A PC Ethernet port
An existing LAN

LED Feedback (AUTO Mode)

During AUTO mode, LED colors indicate the selected role:

Mode Selected	LED Pattern
DHCP Server	Purple ↔ Yellow blink
DHCP Client	Purple ↔ White blink

This provides immediate, headless feedback.

Connection Management

Before activating any mode, NETMODE:

Stops udhcpd (if running)
Finds all active NetworkManager connections bound to end0
Deactivates them cleanly

This ensures only one active network role exists at any time.

Implementation Notes

Uses nmcli con up/down exclusively
Explicit interface binding avoids ambiguity
Logging is sent to syslog using tag LicheeJack
set -o pipefail ensures early failure detection

Integration Ideas

Bind AUTO mode to Mode Switch position
Use in USB gadget payloads with Ethernet
Combine with BATTERY for power-aware networking
Use LED signaling for headless diagnostics

Limitations

AUTO mode relies on passive sniffing, not active probing
Requires tcpdump permission on end0
Assumes preconfigured NetworkManager connection profiles

NETMODE follows the Lichee-Jack philosophy: adaptive, explicit, and automation-first.