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Initial commit: Alpine 5G Router with Fibocom FM350-GL modem configuration

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- Complete working configuration for FM350-GL modem
- CYTA Cyprus APN setup (internet)
- AT command reference and troubleshooting guide
- Configuration scripts and documentation
- RNDIS mode working with manual IP configuration
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nearxos
2026-02-02 00:26:20 +02:00
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# Logs
*.log
/var/log/
# Temporary files
*.tmp
*.swp
*~
# OS files
.DS_Store
Thumbs.db
# Backup files
*.bak
*.backup

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# Fibocom FM350-GL 5G Modem Configuration Guide
Complete reference for configuring the Fibocom FM350-GL modem on Alpine Linux.
## Working Configuration
| Setting | Value |
|---------|-------|
| **Modem** | Fibocom FM350-GL |
| **USB ID** | 0e8d:7126 (Mode 40) |
| **AT Port** | /dev/ttyUSB1 |
| **Network Interface** | eth1 (RNDIS) |
| **APN** | internet (CYTA Cyprus) |
## AT Command Reference
### Sending AT Commands
The FM350-GL doesn't need `stty` configuration. Send commands directly:
```bash
# Pattern for sending AT commands
cat /dev/ttyUSB1 & CAT_PID=$!
sleep 0.3
echo -e 'YOUR_COMMAND\r' > /dev/ttyUSB1
sleep 2
kill $CAT_PID 2>/dev/null
```
### Essential Commands
| Command | Purpose | Example Response |
|---------|---------|------------------|
| `AT` | Test communication | `OK` |
| `AT+CGMI` | Manufacturer | `Fibocom Wireless Inc.` |
| `AT+CGMM` | Model | `FM350-GL` |
| `AT+CSQ` | Signal strength | `+CSQ: 7, 99` (7 = moderate) |
| `AT+CREG?` | Network registration | `+CREG: 0,1` (1 = registered) |
| `AT+CEREG?` | LTE/5G registration | `+CEREG: 0,1` |
| `AT+CCID` | SIM card ID | `+CCID: 893570...` |
### APN Configuration
```bash
# Set APN (CYTA Cyprus uses "internet")
echo -e 'AT+CGDCONT=1,"IP","internet"\r' > /dev/ttyUSB1
# Verify APN is set
echo -e 'AT+CGDCONT?\r' > /dev/ttyUSB1
# Response: +CGDCONT: 1,"IP","internet",""...
```
### Connection Management
```bash
# Activate PDP context (start data connection)
echo -e 'AT+CGACT=1,1\r' > /dev/ttyUSB1
# Response: +CGEV: ME PDN ACT 1, OK
# Get assigned IP address
echo -e 'AT+CGPADDR=1\r' > /dev/ttyUSB1
# Response: +CGPADDR: 1,"10.156.167.104",""
# Get full connection details (DNS, MTU)
echo -e 'AT+CGCONTRDP=1\r' > /dev/ttyUSB1
# Response includes DNS servers
```
### USB Mode Control
```bash
# Check current USB mode
echo -e 'AT+GTUSBMODE?\r' > /dev/ttyUSB1
# Response: +GTUSBMODE: 40
# Available modes
echo -e 'AT+GTUSBMODE=?\r' > /dev/ttyUSB1
# Response: +GTUSBMODE: (40,41)
# Switch modes (requires modem reset)
echo -e 'AT+GTUSBMODE=40\r' > /dev/ttyUSB1
# Reset modem
echo -e 'AT+CFUN=1,1\r' > /dev/ttyUSB1
```
## USB Modes
| Mode | USB Product ID | Description | AT Commands |
|------|----------------|-------------|-------------|
| 40 | 0e8d:7126 | RNDIS mode | ✅ Work on ttyUSB1 |
| 41 | 0e8d:7127 | Extended mode | ❌ Don't work |
**Important:** Stay in Mode 40 for reliable AT command access.
## Network Interface Configuration
### Why DHCP Doesn't Work
The RNDIS interface (`eth1`) does **not** provide DHCP. The modem manages the connection internally. You must:
1. Get the IP from the modem via `AT+CGPADDR=1`
2. Configure the interface manually
### Manual Configuration
```bash
# Get IP from modem (replace with actual value)
MODEM_IP="10.156.167.104"
# Configure interface
ip link set eth1 up
ip addr flush dev eth1
ip addr add $MODEM_IP/32 dev eth1
ip route add default dev eth1 metric 50
# Test
ping -c 3 8.8.8.8
```
## CYTA Cyprus Settings
| Setting | Value |
|---------|-------|
| APN | `internet` |
| DNS Primary | 195.14.130.220 |
| DNS Secondary | 195.14.154.100 |
| Network Name | Vodafone |
## Complete Connection Sequence
```bash
#!/bin/sh
# Full connection sequence for FM350-GL with CYTA SIM
AT_PORT="/dev/ttyUSB1"
APN="internet"
# 1. Configure APN
cat $AT_PORT & PID=$!; sleep 0.3
echo -e "AT+CGDCONT=1,\"IP\",\"$APN\"\r" > $AT_PORT
sleep 2; kill $PID 2>/dev/null
# 2. Activate connection
cat $AT_PORT & PID=$!; sleep 0.3
echo -e "AT+CGACT=1,1\r" > $AT_PORT
sleep 3; kill $PID 2>/dev/null
# 3. Get IP address
MODEM_IP=$(timeout 5 sh -c "
cat $AT_PORT & PID=\$!
sleep 0.3
echo -e 'AT+CGPADDR=1\r' > $AT_PORT
sleep 2
kill \$PID 2>/dev/null
" 2>&1 | grep CGPADDR | grep -oE '[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+' | head -1)
echo "Modem IP: $MODEM_IP"
# 4. Configure interface
ip link set eth1 up
ip addr flush dev eth1
ip addr add $MODEM_IP/32 dev eth1
ip route add default dev eth1 metric 50
# 5. Test
ping -c 3 8.8.8.8
```
## Troubleshooting
### AT Commands Not Responding
**Symptoms:** No response to AT commands on any port.
**Solutions:**
1. Check modem is in Mode 40: `lsusb | grep 7126`
2. If in Mode 41 (7127), AT commands won't work - need physical access to switch back
3. Try different ports: ttyUSB0, ttyUSB1, ttyUSB2
### ttyUSB3 Shows as Regular File
**Symptoms:** `ls -la /dev/ttyUSB3` shows `-rw-r--r--` instead of `crw-rw----`
**Fix:**
```bash
rm -f /dev/ttyUSB3
mknod /dev/ttyUSB3 c 188 3
chmod 660 /dev/ttyUSB3
chown root:dialout /dev/ttyUSB3
```
### stty Errors
**Symptoms:** `stty: /dev/ttyUSB1: cannot perform all requested operations`
**Solution:** Don't use `stty`. Send AT commands directly with `echo` and `cat`.
### No IP on eth1
**Symptoms:** `ip addr show eth1` shows no inet address after DHCP attempt.
**Solution:** RNDIS doesn't use DHCP. Configure IP manually from `AT+CGPADDR=1`.
### ModemManager Not Detecting Modem
**Note:** ModemManager doesn't work well with this modem in RNDIS mode. Use AT commands directly instead.
### Signal Strength Interpretation
| CSQ Value | dBm | Quality |
|-----------|-----|---------|
| 0 | -113 or less | No signal |
| 1-9 | -111 to -95 | Poor |
| 10-14 | -93 to -85 | Fair |
| 15-19 | -83 to -75 | Good |
| 20-30 | -73 to -53 | Excellent |
| 31 | -51 or better | Excellent |
| 99 | Unknown | - |
## Kernel Modules
These modules should be loaded for MBIM/QMI support (optional):
```bash
modprobe cdc-wdm
modprobe cdc_mbim
modprobe qmi_wwan
modprobe cdc_ncm
# Verify
lsmod | grep -E '(cdc|qmi)'
```
## Files on Device
| Path | Purpose |
|------|---------|
| `/usr/local/bin/connect-5g.sh` | Auto-connection script |
| `/etc/init.d/5g-router` | OpenRC service |
| `/var/log/5g-router.log` | Connection log |
| `/etc/iptables/rules.v4` | Firewall/NAT rules |
## Service Management
```bash
# Check status
service 5g-router status
# Restart connection
service 5g-router restart
# View logs
tail -f /var/log/5g-router.log
# Check if enabled at boot
rc-update show | grep 5g-router
```

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# Alpine 5G Router - Raspberry Pi 5 + Fibocom FM350-GL
A complete 5G router setup using Alpine Linux on Raspberry Pi 5 with a Fibocom FM350-GL modem.
## ✅ Status: Working
The 5G modem is fully operational with CYTA Cyprus SIM card.
## Documentation
| File | Description |
|------|-------------|
| [README.md](README.md) | This file - overview and quick start |
| [5G_MODEM_TROUBLESHOOTING.md](5G_MODEM_TROUBLESHOOTING.md) | Complete modem configuration reference |
| [configure_fm350_5g.sh](configure_fm350_5g.sh) | Configuration script for the modem |
## Hardware
- **Board:** Raspberry Pi 5
- **Modem:** Fibocom FM350-GL (USB ID: 0e8d:7126)
- **OS:** Alpine Linux v3.23.3
- **SIM:** CYTA Cyprus (APN: `internet`)
## Network Architecture
```
Internet (CYTA 5G)
│
▼
FM350-GL Modem
(RNDIS eth1)
│
▼
Raspberry Pi 5
Alpine Linux
│
▼
eth0.100 VLAN
(192.168.1.1)
│
▼
LAN Clients
```
## Quick Start
### 1. Install Required Packages
```bash
# Enable community repository
sed -i 's|#.*community|http://mirrors.neterra.net/alpine/v3.23/community|' /etc/apk/repositories
apk update
# Install packages
apk add modemmanager dnsmasq iptables libmbim-tools qmi-utils
```
### 2. Configure and Connect Modem
```bash
# Set APN for CYTA
cat /dev/ttyUSB1 & CAT_PID=$!
sleep 0.3
echo -e 'AT+CGDCONT=1,"IP","internet"\r' > /dev/ttyUSB1
sleep 2
kill $CAT_PID
# Activate connection
cat /dev/ttyUSB1 & CAT_PID=$!
sleep 0.3
echo -e 'AT+CGACT=1,1\r' > /dev/ttyUSB1
sleep 3
kill $CAT_PID
# Get modem IP
cat /dev/ttyUSB1 & CAT_PID=$!
sleep 0.3
echo -e 'AT+CGPADDR=1\r' > /dev/ttyUSB1
sleep 2
kill $CAT_PID
# Note the IP address returned (e.g., 10.156.167.104)
```
### 3. Configure Network Interface
```bash
# Replace MODEM_IP with the IP from AT+CGPADDR=1
MODEM_IP="10.156.167.104"
ip link set eth1 up
ip addr flush dev eth1
ip addr add $MODEM_IP/32 dev eth1
ip route add default dev eth1 metric 50
# Test connectivity
ping -c 3 8.8.8.8
```
### 4. Setup NAT for LAN
```bash
# Enable IP forwarding
echo 1 > /proc/sys/net/ipv4/ip_forward
# Configure NAT
iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE
iptables -A FORWARD -i eth0.100 -o eth1 -j ACCEPT
iptables -A FORWARD -i eth1 -o eth0.100 -m state --state RELATED,ESTABLISHED -j ACCEPT
# Save rules
iptables-save > /etc/iptables/rules.v4
```
## Key Configuration Details
### Modem USB Modes
| Mode | USB ID | Description | Status |
|------|--------|-------------|--------|
| 40 | 0e8d:7126 | RNDIS mode | ✅ Working |
| 41 | 0e8d:7127 | Extended mode | ❌ AT broken |
**Important:** Stay in Mode 40 - AT commands work on `/dev/ttyUSB1`.
### Working AT Commands
| Command | Description |
|---------|-------------|
| `AT` | Test communication |
| `AT+CSQ` | Signal strength |
| `AT+CGDCONT=1,"IP","internet"` | Set APN |
| `AT+CGACT=1,1` | Activate connection |
| `AT+CGPADDR=1` | Get assigned IP |
| `AT+CGCONTRDP=1` | Get DNS servers |
| `AT+GTUSBMODE?` | Check USB mode |
### CYTA Cyprus Network Info
- **APN:** `internet`
- **DNS Primary:** 195.14.130.220
- **DNS Secondary:** 195.14.154.100
## Services
The following services are configured to start on boot:
```bash
# Check service status
rc-status
# Services enabled:
# - dnsmasq (DHCP/DNS)
# - iptables-restore (firewall rules)
# - 5g-router (connection script)
```
## Files on Device
| Path | Purpose |
|------|---------|
| `/usr/local/bin/connect-5g.sh` | Startup connection script |
| `/etc/init.d/5g-router` | OpenRC service |
| `/etc/init.d/iptables-restore` | Firewall restore service |
| `/etc/iptables/rules.v4` | Saved firewall rules |
| `/etc/dnsmasq.conf` | DHCP configuration |
| `/etc/network/interfaces` | Network configuration |
| `/var/log/5g-router.log` | Connection log |
## Troubleshooting
### Modem not responding to AT commands
1. Check modem is in Mode 40: `lsusb | grep 7126`
2. Use `/dev/ttyUSB1` for AT commands
3. Don't use `stty` - send commands directly
### DHCP not working on eth1
This is normal - RNDIS mode doesn't provide DHCP. Configure IP manually using the address from `AT+CGPADDR=1`.
### Connection drops
Re-run the connection script:
```bash
/usr/local/bin/connect-5g.sh
```
Or restart the service:
```bash
service 5g-router restart
```
## Verification Commands
```bash
# Check modem
lsusb | grep -i fibocom
# Check network
ip addr show eth1
ip route show
# Test connectivity
ping -c 3 8.8.8.8
ping -c 3 google.com
# Check NAT rules
iptables -t nat -L -n -v
# View logs
tail -f /var/log/5g-router.log
```

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#!/bin/bash
# Fibocom FM350-GL 5G Modem Configuration Script
# For Alpine Linux with CYTA Cyprus SIM card
#
# This script configures the 5G modem and establishes a connection
# Usage: ./configure_fm350_5g.sh
set -e
# Configuration
AT_PORT="/dev/ttyUSB1"
APN="internet"
WAN_IF="eth1"
LAN_IF="eth0.100"
# Colors for output
RED='\033[0;31m'
GREEN='\033[0;32m'
YELLOW='\033[1;33m'
NC='\033[0m' # No Color
log_info() { echo -e "${GREEN}[INFO]${NC} $1"; }
log_warn() { echo -e "${YELLOW}[WARN]${NC} $1"; }
log_error() { echo -e "${RED}[ERROR]${NC} $1"; }
send_at_cmd() {
local cmd="$1"
local wait="${2:-2}"
cat $AT_PORT 2>/dev/null &
local CAT_PID=$!
sleep 0.3
echo -e "${cmd}\r" > $AT_PORT
sleep $wait
kill $CAT_PID 2>/dev/null || true
}
get_at_response() {
local cmd="$1"
local wait="${2:-2}"
timeout $((wait + 3)) sh -c "
cat $AT_PORT 2>/dev/null &
CAT_PID=\$!
sleep 0.3
echo -e '${cmd}\r' > $AT_PORT
sleep $wait
kill \$CAT_PID 2>/dev/null
" 2>&1
}
check_modem() {
log_info "Checking for FM350-GL modem..."
if ! lsusb | grep -qi "fibocom"; then
log_error "Fibocom modem not detected via USB"
exit 1
fi
local usb_id=$(lsusb | grep -i fibocom | grep -oE '0e8d:[0-9a-f]+')
log_info "Modem detected: $usb_id"
if [ "$usb_id" = "0e8d:7127" ]; then
log_warn "Modem is in Mode 41 (7127). AT commands may not work."
log_warn "Attempting to switch to Mode 40..."
fi
if [ ! -c "$AT_PORT" ]; then
log_error "AT port $AT_PORT not available"
exit 1
fi
log_info "AT port available: $AT_PORT"
}
test_at_commands() {
log_info "Testing AT command communication..."
local response=$(get_at_response "AT" 1)
if echo "$response" | grep -q "OK"; then
log_info "AT communication working"
return 0
else
log_error "AT commands not responding"
return 1
fi
}
check_signal() {
log_info "Checking signal strength..."
local response=$(get_at_response "AT+CSQ" 1)
local csq=$(echo "$response" | grep "+CSQ:" | grep -oE '[0-9]+' | head -1)
if [ -n "$csq" ]; then
if [ "$csq" -lt 10 ]; then
log_warn "Signal strength: $csq (weak)"
elif [ "$csq" -lt 20 ]; then
log_info "Signal strength: $csq (moderate)"
else
log_info "Signal strength: $csq (good)"
fi
else
log_warn "Could not read signal strength"
fi
}
configure_apn() {
log_info "Configuring APN: $APN"
local response=$(get_at_response "AT+CGDCONT=1,\"IP\",\"$APN\"" 2)
if echo "$response" | grep -q "OK"; then
log_info "APN configured successfully"
else
log_warn "APN configuration may have failed"
fi
}
activate_pdp() {
log_info "Activating PDP context..."
local response=$(get_at_response "AT+CGACT=1,1" 3)
if echo "$response" | grep -qE "(OK|CGEV)"; then
log_info "PDP context activated"
else
log_warn "PDP activation response: $response"
fi
}
get_modem_ip() {
log_info "Getting modem IP address..."
local response=$(get_at_response "AT+CGPADDR=1" 2)
local ip=$(echo "$response" | grep "+CGPADDR:" | grep -oE '[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+' | head -1)
if [ -n "$ip" ]; then
log_info "Modem IP: $ip"
echo "$ip"
else
log_error "Could not get modem IP"
return 1
fi
}
configure_interface() {
local ip="$1"
log_info "Configuring network interface $WAN_IF..."
ip link set $WAN_IF up 2>/dev/null || true
ip addr flush dev $WAN_IF 2>/dev/null || true
ip addr add $ip/32 dev $WAN_IF
ip route add default dev $WAN_IF metric 50 2>/dev/null || true
log_info "Interface configured with IP: $ip"
}
setup_nat() {
log_info "Setting up NAT for LAN ($LAN_IF)..."
# Enable IP forwarding
echo 1 > /proc/sys/net/ipv4/ip_forward
# Add NAT rules (check if they exist first)
iptables -t nat -C POSTROUTING -o $WAN_IF -j MASQUERADE 2>/dev/null || \
iptables -t nat -A POSTROUTING -o $WAN_IF -j MASQUERADE
iptables -C FORWARD -i $LAN_IF -o $WAN_IF -j ACCEPT 2>/dev/null || \
iptables -A FORWARD -i $LAN_IF -o $WAN_IF -j ACCEPT
iptables -C FORWARD -i $WAN_IF -o $LAN_IF -m state --state RELATED,ESTABLISHED -j ACCEPT 2>/dev/null || \
iptables -A FORWARD -i $WAN_IF -o $LAN_IF -m state --state RELATED,ESTABLISHED -j ACCEPT
log_info "NAT configured"
}
test_connectivity() {
log_info "Testing internet connectivity..."
if ping -c 3 8.8.8.8 >/dev/null 2>&1; then
log_info "Ping to 8.8.8.8: SUCCESS"
else
log_error "Ping to 8.8.8.8: FAILED"
return 1
fi
if ping -c 2 google.com >/dev/null 2>&1; then
log_info "DNS resolution: SUCCESS"
else
log_warn "DNS resolution failed - check /etc/resolv.conf"
fi
}
show_status() {
echo ""
echo "========================================="
echo " 5G Modem Configuration Summary "
echo "========================================="
echo ""
echo "Modem: $(lsusb | grep -i fibocom | cut -d' ' -f6-)"
echo "AT Port: $AT_PORT"
echo "APN: $APN"
echo ""
echo "Interface: $WAN_IF"
ip addr show $WAN_IF 2>/dev/null | grep -E "(state|inet )" | sed 's/^/ /'
echo ""
echo "Routing:"
ip route show | grep -E "(default|$WAN_IF)" | sed 's/^/ /'
echo ""
echo "========================================="
}
# Main execution
main() {
log_info "Starting FM350-GL 5G modem configuration..."
echo ""
check_modem
test_at_commands || exit 1
check_signal
configure_apn
activate_pdp
local modem_ip=$(get_modem_ip)
if [ -z "$modem_ip" ]; then
log_error "Failed to get modem IP. Exiting."
exit 1
fi
configure_interface "$modem_ip"
setup_nat
test_connectivity
show_status
log_info "5G modem configuration complete!"
}
main "$@"