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npm License: MIT

Glass Glass

  • Glass was created as a quick side project out of necessity to fulfill requirements not readily available through our production ISC DHCP Servers for our organization - I've decided to share it for anyone who would also find it useful
  • More features and application-level things could be extended into the interface but my goals were simply the high yield features for our production network needs
  • Disclaimer: Glass and its author has no affiliation with ISC and the authors of isc-dhcp-server
  • Original Author: Chris Miles:

Table of Contents


  • Standalone NodeJS application that has a web interface, listens to the dhcp log and the leases file to collect analytics and data realtime
  • DHCP IPv4 Support (No IPv6 at this time)
  • Full OUI Database
    • Has complete vendor to MAC OUI database - with a script to pull down and update live data
  • Realtime Alerting
    • Shared Subnet Utilization Alerting
      • Customize thresholds (IE: Warning: 80% Critical 95%)
    • Leases Per Minute - If your disk fills up - or your SAN is unavailable - alerting your team on absolutely zero activity on your production server can allow you to be on the 8-ball. This is a step-above process alerting because you can have the dhcp server process running and no leases being written
  • Alerting Destinations
    • Slack
    • E-Mail
    • SMS
  • Statistics (Available through REST API)
    • Shared Network Utilization
    • Individual Network Utilization
    • Vendor Counts by MAC
    • OUI Count
    • Excessive DHCP Requests
  • Log Streaming (Realtime via Websockets)
  • Lease Data
    • Full active DHCP lease data available via API and searchable through the web interface
    • All options are dynamically parsed into an easy to ingest JSON format
  • Config Edit (Only supports single DHCP config file configurations)
    • Edit the DHCP config using a full web-based text editor (Ace)
    • Before saving the config - Glass will run a syntax check against the file
    • Config editing through Glass creates a backup (snapshot) on success with no syntax errors and commits to production file * Start / Stop / Restart server process * Administrative Authentication enforced on administrative tasks (Restarts/Config/Glass Settings)
  • Uses AdminBSB UI with customizations and tweaks
  • Full Mobile support


  • Glass has a dashboard containing quick-glance important information pertaining to the health of the server and the pools configured - statistics update in realtime
    • DHCP Leases per second / minute
    • Total Active Leases
    • Server CPU Utilization
    • Shared Network Utilization
    • Subnet Utilization


DHCP Config Editing

  • A built in config web editor that uses the dhcp server binary to check syntax before over-writing the production config with a bad configuration
  • Currently config editing only supports editing one single config file (No includes) due to syntax verification that glass performs


DHCP Config Snapshots

  • Mess up a config? Snapshots are quickly available through the snapshots sidebar as long as you've been editing the config through the Glass interface


DHCP Server Restart

  • Server Stop / Start / Restarting can all be done through the Glass interface



  • Glass exposes useful statistical information in the Web interface that is also available through the raw API interface


Log Streaming

  • Stream the DHCP syslog via Websockets to your browser, making troubleshooting efforts super easy by being able to add realtime filters and have MAC address be translated realtime to the vendor for readability



Glass API

  • Glass has a small but powerful REST API exposing data not otherwise available easily through raw isc-dhcp-server data formats



  • Realtime Alerting One of our biggest high value returns on this project was creating something that can keep us on top of any sort of outage issues.
    • "Is our server writing leases even though the process is alive?"
    • "Is any our shared networks filling up?"
  • Shared Subnet Utilization Alerting (Checked once a minute)
    • Customize thresholds
      • Default 80 (Warning)
      • Default 95 (Critical)
  • Leases Per Minute (Checked once every 5 seconds) - If your disk fills up - or your SAN is unavailable - alerting your team on absolutely zero activity on your production server can allow you to be on the 8-ball. This is a step-above process alerting because you can have the dhcp server process running and no leases being written.
    • Default: 50
    • Glass keeps track of a rolling average of leases being written on the minute, the counter can be seen realtime on the dashboard
  • 0 value in Glass Settings or in your glass_config.json will turn the alerting functionality OFF

Alert Delivery Methods

  • Glass currently supports the following alerting delivery methods



SMS - Simple Format

  • SMS gets cut off at 140 characters - but you get the core alert and should only be used as a backup measure to other methods


  • Instructions are per Debian/Ubuntu Distros

Install NodeJS (If not installed)

curl -sL | sudo -E bash -
sudo apt-get install -y nodejs

Install Glass (as root)

cd /opt
git clone
cd glass-isc-dhcp
mkdir logs
chmod u+x ./bin/ -R
chmod u+x *.sh

sudo npm install
sudo npm install forever -g
sudo npm start
  • For Debian this is all that is needed and Glass should start immediately, you can browse via http://server-ip:3000
  • For Ubuntu users - you will have additional Apparmor config to add
  • Recommended to iptables port 3000 to close off Glass if you are facing the public on your server
  • Recommended to keep Glass up through reboots, see Glass Process Keepalive


  • Ubuntu uses AppArmor by default - you will most likely run into file access issues without exemptions
sed -i '/\/etc\/dhcp\/\*\*/a\ \ \/var\/lib\/dhcp\/\*\* lrw,' /etc/apparmor.d/usr.sbin.dhcpd 
sed -i '/\/etc\/dhcp\/\*\*/a\ \ \/opt\/glass-isc-dhcp\/\*\* lrw,' /etc/apparmor.d/usr.sbin.dhcpd 
service apparmor restart

Glass Configuration

  • Glass configuration is stored in ./config/glass_config.json
  • All of these settings can be edited in both Glass Settings and Glass Alerts within the Web Interface, if you have custom file locations you will need to edit this config file before starting


  "admin_user": "glassadmin",
  "admin_password": "glassadmin",
  "leases_file": "/var/lib/dhcp/dhcpd.leases",
  "log_file": "/var/log/dhcp.log",
  "config_file": "/etc/dhcp/dhcpd.conf",
  "shared_network_critical_threshold": "95",
  "shared_network_warning_threshold": "0",
  "slack_webhook_url": "",
  "slack_alert_channel": "",
  "leases_per_minute_threshold": "50",
  "ip_ranges_to_allow": [
  "email_alert_to": "",
  "sms_alert_to": ""

Glass Process Keepalive

  • To keep your server alive through reboots, possible crashes and process restarts, we need to use a process monitor and for simplicity we will use NodeJS's Forever. Forever is already installed during Glass installation. We will add it to our crontab
crontab -l > mycrontab
echo "@reboot cd /opt/glass-isc-dhcp && /usr/bin/forever --minUptime 10000 --spinSleepTime 10000 -a -o ./logs/glass-process.log -e ./logs/glass-error.log ./bin/www" >> mycrontab
crontab mycrontab
rm mycrontab

Secure your Server

  • Glass runs on web port 3000 - if you're going to run this on a production server, make sure that you lock it down from the outside world if anyone can access it. Even if they don't have a password - vulnerabilities can surface at any point in the future and your system becomes a prime target

iptables (Recommended)

iptables -A INPUT -p tcp --dport 3000 -s -j ACCEPT
iptables -A INPUT -p tcp --dport 3000 -s x.x.x.x/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 3000 -j REJECT --reject-with icmp-port-unreachable

Building dhcpd-pools (Optional)

  • Glass uses dhcpd-pools for shared network / subnet utilization and it is bundled by default (For Ubuntu and Debian) when you install. However, if you need to build the binary yourself on another distribution, use the following to build dhcpd-pools and it needs to be placed in the ./bin directory of glass
  • Below shows use of apt-get of unzip/libtool - you will have to use your respective package management system to pull pre-requisites down
  • Credit: dhcpd-pools:
sudo apt-get install -y unzip
sudo apt-get install -y libtool

git clone

cd /tmp

cd /tmp/dhcpd-pools
./bootstrap	# only when building git clone
./configure --with-uthash=/tmp/uthash-master/include
make -j4
make check
make install

Glass API

Use Cases

  • If none of the in-web management features are appealing - at the very least the exposed real time data the Glass agent can expose via the API can be valuable in integrating with 3rd party applications. For example - if you need to query 5 DHCP servers for one device on a network - this makes it incredibly efficient to do so with real-time and accurate data
  • If you want to get all subnet details/utilization exposed into a 3rd party application, (For example graphing utilization in grafana) you can use the API calls to ingest into your InfluxDB or otherwise

Example Calls

GET: /api/get_active_leases

  • This call will return the full lease list unless you pass optional search parameter:
    • Ex: /api/get_active_leases?search=Cisco

Output example truncated - some info redacted

  "64.90.X.X": {
    "start": 1507177832,
    "end": 1507181432,
    "mac": "14:91:82:6e:77:0a",
    "mac_oui_vendor": "Belkin International Inc.",
    "options": {
      "ClientMac": "14:91:82:6e:77:a",
      "ClientIP": "64.90.X.X",
      "vendor-class-identifier": "udhcp 1.19.4",
      "vendor-string": "udhcp 1.19.4",
      "agent.remote-id": "3:c:0:0:d1:d4:29:81:f6:3:2:8a:0:be"
    "host": "Vargo"
  "209.212.X.X": {
    "start": 1507177401,
    "end": 1507181001,
    "mac": "20:aa:4b:12:bd:9b",
    "mac_oui_vendor": "Cisco-Linksys, LLC",
    "options": {
      "ClientMac": "20:aa:4b:12:bd:9b",
      "ClientIP": "209.212.X.X",
      "agent.remote-id": "3:c:0:0:d1:d4:29:81:f6:3:1:4e:4:51"
    "host": "snarley55"

GET: /api/get_subnet_details

Output example truncated - some info redacted

  "subnets": [
      "location": "69.168.x.x/26",
      "range": "69.168.x.x - 69.168.x.x",
      "defined": 55,
      "used": 0,
      "touched": 0,
      "free": 55
      "location": "",
      "range": " -",
      "defined": 2045,
      "used": 0,
      "touched": 0,
      "free": 2045

GET: /api/get_mac_oui_list

Output example truncated - some info redacted

  "100000": "Private",
  "100723": "IEEE Registration Authority",
  "101212": "Vivo International Corporation Pty Ltd",
  "101218": "Korins Inc.",
  "101248": "ITG, Inc.",
  "101250": "Integrated Device Technology (Malaysia) Sdn. Bhd.",
  "101331": "Technicolor",
  "102279": "ZeroDesktop, Inc.",

GET: /api/get_server_info

Output example

  "cpu_utilization": 3.1,
  "leases_per_second": 4,
  "leases_per_minute": 310,
  "host_name": "DHCP-Server"

GET: /api/get_vendor_count

Output example truncated

  "Belkin International Inc.": 1230,
  "Cisco-Linksys, LLC": 1345,
  "Calix Inc.": 4368,
  "Billion Electric Co. Ltd.": 404,
  "Apple, Inc.": 528,
  "Wistron Corporation": 18,
  "Zyxel Communications Corporation": 320,
  "Billion Electric Co., Ltd.": 611,
  "NETGEAR": 2797,
  "Cisco Systems, Inc": 65,
  "Hewlett Packard": 87,
  "Sonicwall": 11,

GET: /api/get_mac_oui_count_by_vendor

Output example truncated

  "149182": {
    "count": 131,
    "mac_prefix": "149182",
    "vendor": "Belkin International Inc."
  "180373": {
    "count": 4,
    "mac_prefix": "180373",
    "vendor": "Dell Inc."
  "186590": {
    "count": 1,
    "mac_prefix": "186590",
    "vendor": "Apple, Inc."

GET: /api/get_dhcp_requests

Output example truncated - some info redacted

  "20:aa:4b:1d:d0:17": {
    "request_for": "68.170.X.X",
    "request_via": "209.212.X.X",
    "request_count": 139,
    "request_vendor": "Cisco-Linksys, LLC"
  "58:6d:8f:aa:37:6a": {
    "request_for": "68.170.X.X",
    "request_via": "209.212.X.X",
    "request_count": 171,
    "request_vendor": "Cisco-Linksys, LLC"