contact supportVoIP Detective can be monitored by any SNMP-based tool such as PRTG, SolarWinds, Zabbix, LibreNMS or Nagios. The appliance exposes standard system information (uptime, CPU, memory, disk, network interfaces and running processes) over SNMP v2c or SNMP v3. SNMP is read-only – a monitoring tool can read values from VoIP Detective but cannot change anything.
Everything in this article is done from the VoIP Detective command line menu (CLI). Log in over SSH as the cliadmin user to reach it.
Requirements
| Item | Requirement |
|---|---|
| VoIP Detective OS | AlmaLinux 9 (OS 4 or later). CentOS 7 and CentOS 8 appliances can be configured, but package installation on those systems requires support assistance. |
| Port | UDP 161 inbound from your monitoring server. The CLI opens this port on the appliance firewall automatically. |
| Package | net-snmp and net-snmp-utils. These are installed automatically the first time SNMP is enabled. The appliance needs outbound HTTPS (port 443) to the AlmaLinux repositories to download them. Air gapped installation should contact VoIP Detective support for assistance. |
| Monitoring tool | Any SNMP v2c or v3 poller. SNMP v3 is recommended. |
Important: SNMP v2c sends the community string in clear text. Use SNMP v3 unless your monitoring tool does not support it.
Enable SNMP
From the CLI main menu, select 5 (configure Linux OS services), then 8 (configure SNMP), then 2 (enable and configure SNMP).
The first time this runs, VoIP Detective installs the net-snmp packages. This takes about a minute. You are then asked which version of SNMP to configure.
SNMP v3 (recommended)
Choose 2 (SNMPv3) and answer the prompts:
| Prompt | What to enter |
|---|---|
| SNMPv3 username | The account name your monitoring tool will log in with, for example prtg. |
| Authentication password | At least 8 characters. Entered twice. This proves the monitoring tool's identity. |
| Privacy (encryption) password | At least 8 characters. Entered twice. This encrypts the SNMP traffic. It can be the same as the authentication password, but a different one is better. |
| System location | Free text shown to the monitoring tool, for example Head Office - Rack 4. |
| System contact | Free text, usually an email address. |
VoIP Detective then creates the user, opens UDP 161 on the firewall, starts the SNMP service and runs a test query against itself. Look for this line near the end:
[OK] SNMPv3 test query worked: ...
If you see [FAIL] instead, the user was not created correctly. Run option 2 again.
ℹ️ Tip: Passwords are typed without echo – nothing appears on screen as you type.
SNMP v2c
Choose 1 (SNMPv2c) and answer the prompts:
| Prompt | What to enter |
|---|---|
| Read-only community string | The shared password your monitoring tool will use. Do not use public. |
| Allowed network/host | The IP address or network that is permitted to poll VoIP Detective, for example 192.168.1.50 or 10.0.0.0/24. Entering default allows any host and is not recommended. |
| System location | Free text shown to the monitoring tool. |
| System contact | Free text, usually an email address. |
VoIP Detective writes the configuration, opens UDP 161 on the firewall and starts the SNMP service.
ℹ️ Tip: Running option 2 again replaces the previous SNMP configuration. A dated backup of the old file is kept in /etc/snmp/.
Configure your monitoring tool
The values below are set by VoIP Detective when the SNMPv3 user is created and cannot be changed from the CLI.
SNMP v3 settings
| Setting | Value |
|---|---|
| SNMP version | v3 |
| Security level | authPriv (authentication and encryption). VoIP Detective refuses noAuthNoPriv and authNoPriv. |
| Username | The SNMPv3 username you entered |
| Authentication protocol | SHA (SHA-1). Do not select SHA-256 or SHA-512. |
| Authentication password | The authentication password you entered |
| Encryption / privacy protocol | AES (AES-128). Do not select AES-192 or AES-256. |
| Encryption / privacy password | The privacy password you entered |
| Context name | Leave blank |
| Port | 161 UDP |
ℹ️ Tip: In PRTG these are labelled Authentication Type, Password, Encryption Type and Data Encryption Key on the Credentials for SNMP Devices page of the device. Set them on the device, not on each sensor.
SNMP v2c settings
| Setting | Value |
|---|---|
| SNMP version | v2c |
| Community string | The read-only community string you entered |
| Port | 161 UDP |
Recommended sensors
VoIP Detective supports the standard SNMP system MIBs (SNMPv2-MIB, HOST-RESOURCES-MIB, IF-MIB, UCD-SNMP-MIB). Useful things to monitor:
- Uptime – detects unexpected reboots.
- Disk space on / – CDR data grows over time; alert at 85% used.
- Memory – the database caches heavily, so high usage is normal; alert on swap use instead.
- CPU load – spikes during nightly imports and large reports are expected.
- Network interface traffic – confirms CDR files are still arriving from CUCM.
- Processes –
httpd,php-fpm,mariadbd(ormysqld) andsshdshould always be running.
Check SNMP status
From the CLI main menu, select 5, then 8, then 1 (show current SNMP status). This shows whether the net-snmp package is installed, whether the service is running and enabled at boot, whether UDP 161 is open on the firewall, and the current configuration (community strings are shown; SNMPv3 passwords are not).
Disable SNMP
From the CLI main menu, select 5, then 8, then 3 (disable SNMP). This stops the SNMP service, prevents it from starting at boot and closes UDP 161 on the firewall. The configuration and the net-snmp packages are left in place, so SNMP can be re-enabled later with option 2.
Troubleshooting
"net-snmp package: NOT installed" after running option 2
The package download failed. Option 2 continues past the failure and still asks the SNMP questions, so it can look as though setup completed. Scroll back through the output for a red FAILED line after installing net-snmp.
Installing SNMP without internet access
If the appliance cannot reach the internet contact support, and we will provide the rpms that need to be installed manually.
The SNMPv3 test query failed
The user was not created. The usual cause is that net-snmp was not installed (see above). Confirm with 5 > 8 > 1, fix the installation, then run option 2 again.
The monitoring tool cannot connect
- Run 5 > 8 > 1 and confirm the service is active and
161/udpappears under firewall ports. - Check that UDP 161 is allowed between the monitoring server and VoIP Detective on any network firewall in between.
- SNMP v3: confirm the tool is set to SHA and AES (not the 256-bit variants) and to authPriv.
- SNMP v2c: confirm the monitoring server's IP address falls inside the allowed network you entered. Re-run option 2 to change it.
SNMP shows as enabled but the firewall port is open and the package is missing
Option 2 was run before the package download problem was fixed. The firewall rule and configuration file it left behind are harmless. Fix the download (above) and run option 2 again – it overwrites the configuration.
Security notes
- SNMP on VoIP Detective is read-only. No write community or write user is created.
- SNMP v2c access is limited to the network you entered. SNMP v3 access is not limited by network – any host that can reach UDP 161 and has the credentials can read. Restrict UDP 161 to your monitoring server on your network firewall if required.
- Call records are never exposed over SNMP. Only operating system statistics are available.
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