NTP-GPS

A bare minimum GPS Stratum 1 NTP server, using an inexpensive ($7-15) USB-A GPS reciever

About:

This container runs NTPsec and gpsd, built on the Docker Alpine image.

- USB Reciever -

Tested using the VK-162 GMOUSE USB External GPS Navigation Module [u-blox]

 

Chipset properties

Main chip: u-blox
Receive frequency: L1 [1575.42MHz]
Tracking Channels: 50
Support DGPS [WAAS, EGNOS, and MSAS]

- Configure -

Discover Reciever Mounted Path

Running the following bash script will display what USB devices are connected and path they're mounted

Take note of the /dev/<Device> location

for sysdevpath in $(find /sys/bus/usb/devices/usb*/ -name dev); do (
   syspath="${sysdevpath%/dev}"
   devname="$(udevadm info -q name -p $syspath)"
   [[ "$devname" == "bus/"* ]] && exit
   eval "$(udevadm info -q property --export -p $syspath)"
   [[ -z "$ID_SERIAL" ]] && exit
   echo -e "\n### $ID_SERIAL ###\n/dev/$devname"
) done

Example:

$> for sysdevpath in $(find /sys/bus/usb/devices/usb*/ -name dev); do (
>    syspath="${sysdevpath%/dev}"
>    devname="$(udevadm info -q name -p $syspath)"
>    [[ "$devname" == "bus/"* ]] && exit
>    eval "$(udevadm info -q property --export -p $syspath)"
>    [[ -z "$ID_SERIAL" ]] && exit
>    echo -e "\n### $ID_SERIAL ###\n/dev/$devname"
> ) done

### u-blox_AG_-_www.u-blox.com_u-blox_7_-_GPS_GNSS_Receiver ###
/dev/ttyACM0

### u-blox_AG_-_www.u-blox.com_u-blox_7_-_GPS_GNSS_Receiver ###
/dev/ttyACM1

- Install -

Auto Configure:

The following will mount all devices in /dev to the container, and gpsd will default to USB hotplugging to add new USB devices automatically to the daemon

docker run -d \
  --name=ntp-gps \
  --restart=unless-stopped \
  --cap-add SYS_TIME \
  --device=/dev/ \
  -e TZ=$(cat /etc/timezone) \
  -p 123:123/udp \
fitzdockerhub/ntp-gps:latest

Single Device Configure:

Change <Device ID> to what was previously discovered
Change <Time Zone> to your Time Zone

• List of Time Zones

docker run -d \
  --name=ntp-gps \
  --restart=unless-stopped \
  --cap-add SYS_TIME \
  --device=/dev/<Device ID> \
  -e DEVICE=/dev/<Device ID> \
  -e TZ=<Time Zone> \
  -p 123:123/udp \
fitzdockerhub/ntp-gps:latest

Example:

docker run -d \
  --name=ntp-gps \
  --restart=unless-stopped \
  --cap-add SYS_TIME \
  --device=/dev/ttyACM1 \
  -e DEVICE=/dev/ttyACM1 \
  -e TZ=America/Denver \
  -p 123:123/udp \
ntp-gps:latest

Test NTP Server

Using the built in nmap ntp-info script, the NTP server response can be checked

nmap --script ntp-info -p 123 -sUV -PN <Docker NTP-GPS  Host IP>

Example:

$> nmap --script ntp-info -p 123 -sUV -PN 192.168.0.1

Nmap scan report for 192.168.0.1
Host is up (0.0011s latency).

PORT    STATE SERVICE VERSION
123/udp open  ntp     NTP v4 (primary server)
| ntp-info:
|_  receive time stamp: 2022-12-17T04:29:05
MAC Address: 0A:0A:0A:0A:0A:0A (Unknown)

Nmap done: 1 IP address (1 host up) scanned in 10.64 seconds

- DHCP -

If you are using a local dhcp server such as Dnsmasq or Pi-hole, you can add the DHCP option 42 to advertise the NTP server to all DHCP clients

Change <NTP Server IP> to the address assigned the NTP-GPS container

dhcp-option=42,<NTP Server IP>

Pi-hole Example:

Add a new sequencial <Dnsmasq Filename>.conf file to /etc/dnsmasq.d/

$> ls -1a /etc/dnsmasq.d/
.
..
01-pihole.conf
02-pihole-dhcp.conf
03-pihole-wildcard.conf
04-pihole-static-dhcp.conf

$> echo "dhcp-option=42,192.168.0.1" /etc/dnsmasq.d/05-pihole-ntp-dhcp.conf

Testing DHCP Option 42

Using the built in nmap dhcp-discover script, you can view if the NTP server is being advertised

nmap -sU -p 67 --script=dhcp-discover <DHCP Server IP>

Example:

$> nmap -sU -p 67 --script=dhcp-discover 192.168.0.1

Nmap scan report for 192.168.0.1
Host is up (0.0010s latency).

PORT   STATE SERVICE
67/udp open  dhcps
| dhcp-discover:
|   DHCP Message Type: DHCPACK
|   Server Identifier: 192.168.0.1
|   IP Address Lease Time: 1m42s
|   Subnet Mask: 255.255.255.0
|   Broadcast Address: 192.168.0.255
|   Domain Name Server: 192.168.0.1
|   NTP Servers: 192.168.0.1
|_  Router: 192.168.0.1
MAC Address: 0A:0A:0A:0A:0A:0A (Unknown)

Nmap done: 1 IP address (1 host up) scanned in 0.49 seconds