An SNMP Community String serves as a vital key, enabling secure communication between network devices and management systems. This introductory guide demystifies its function and explores the mechanics of how it ensures network security and efficient management.
Table of contents:
What are SNMP Community Strings?
An SNMP community string is a simple password that SNMP uses to control access to devices, and the passwords involved are known as SNMP community strings.
In other words, SNMP community strings leverage a user ID or password to access the router or other device information. They are only available with SNMPv1 and SNMPv2c protocols. SNMPv3 requires username/password authentication as well as an encryption key.
Many SNMPv1 and v2c devices are shipped with a “public” read-only community string. Most network administrators customize the community strings in the device settings as a best practice.
How SNMP Community Strings Work?
SNMP community strings are sent from one device to another alongside a specially formatted GET request known as a Protocol Data Unit, or PDU. If the community string is correct, the polled device responds with the relevant information as a Response PDU.
SNMP community strings are integral to the security of the Simple Network Management Protocol (SNMP) protocol. What’s more, it helps you to hierarchically manage devices and command your network with confidence
If you’re just getting familiar with SNMP, then head over to our article on How SNMP Works. Additionally, you’ll find information about what can Domotz do for you using SNMP monitoring.
What are the Three Types of SNMP Community Strings?
Community strings come in three primary flavors: read-only, read-write, and trap.
Read-Only
Community Strings:
These allow you to view information about a device but not make any changes.
Read-Write
Community Strings:
These enable you to view and change information on a device.
SNMP community strings can be anywhere from 1 to 32 characters long. Like most passwords, they’re case-sensitive and can include any combination of letters, numbers, and symbols.
What are the SNMP Versions?
The SNMP versions are SNMPv1, SNMPv2c, and SNMPv3. SNMP has undergone a few iterations since its introduction just before the turn of the century.
Although the earliest versions, SNMPv1 and SNMPv2, used community strings, they weren’t as secure as the latest SNMPv3.
Long story short, their lack of encryption made transmissions more vulnerable despite community strings. SNMPv3 offers the highest level of security through encryption, authentication, and message integrity – so it’s best to stick to SNMPv3 and follow safe password practices.
How to Find SNMP Credentials
The first step in finding SNMP credentials is to check with the hardware manufacturer. They should have documentation that includes the default community strings for their devices.
If you can’t find the information from the manufacturer, you can try looking for it online. There are a few different ways to do this:
- Use a search engine like Google or Bing. Try searching for “[device name] SNMP community string.”
- Check online forums for your device. People often post community strings they’ve used for different devices.
Next, we’ll cover some OS-specific strategies:
How to Find SNMP Credentials in Linux
You can store SNMP community strings in the “/etc/snmp/snmpd.conf” file. If you’re on an OS that isn’t configured this way for some reason, you can open a terminal and enter the following command:
find /etc -name snmpd.conf
This will search your entire system for the snmpd.conf file. Once you’ve found the file, open it in a text editor – or view it on the command line using the cat command – and look for a line that starts with “rocommunity”. This line will have the read-only community string for your device. To find the read-write community string, look for a line that starts with “rwcommunity.”
How to Find SNMP Credentials in Windows
Click the appropriate taskbar item to enable the Server Manager. Next, choose the Server Manager tile from the start screen, pick “add Roles and Features,” and navigate to the Features section.
After installing the SNMP service, run the services.msc task after logging in as an administrator. You should see an SNMP Service Properties window pop up – navigate to the Security tab to check the current community string settings under “Accepted community names.”
This should work for Windows 10, Server 2016, and Server 2019, but if you’re using an older version, you’ll have to go through the Windows Key and then navigate to Administrative Tools. You must select the Services option from there to find the SNMP Service Properties window.
How to Configure SNMP Community Strings
Why Configure SNMP Community Strings?
Proper configuration of SNMP community strings ensures:
- Network Security: Prevents unauthorized access to your network devices.
- Efficient Monitoring: Ensures that your NMS can access the required data.
The process for configuring SNMP community strings is different for the various device or software. However, there are some general steps that you can follow.
General Steps
- Access the Device Configuration Interface: Log in to the device using an appropriate method (e.g., SSH, console, or web interface).Locate the SNMP Configuration Section: Navigate to the SNMP settings. This is usually under “Management” or “Monitoring.”
- Set the Community Strings: Define the Read-Only community string (e.g., “public”). Define the Read-Write community string (e.g., “private”).
- Specify Access Control: Restrict access to the community strings by defining permitted IP addresses or subnets.
- Save the Configuration: Apply and save the changes to ensure the settings persist after a reboot.
How to Configure SNMP Community Strings in Linux
Use your preferred editor to modify the “/etc/snmp/snmpd.conf” file.
To create a new community string, add a line that starts with the appropriate read-only or read-write prefix followed by the community string. For example, to create a read-only community string called “public,” you would add the following line to the snmpd.conf file:
rocommunity public
To create a read-write community string, use the “rwcommunity” line instead:
rwcommunity private
On Red Hat this would be it, but with Ubuntu, you should also modify the “/etc/default/snmpd” file by replacing the following line:
SNMPSDOPTS=‘ -lsd -Lf dev/null -u snmp -p /var/run/snmpd.pid’
With:
SNMPDOPTS=‘ -Lsd -Lf /dev/null -u snmp -I -smux -p /var/run/snmpd/pid -c /etc/snmp/snmpd/conf’
After saving and closing the file, restart the SNMP daemon and enable the service with the following commands:
/etc/init.d/snmpd restart
sysv-rc-conf snmpd on
Tip: When you check the snmpd.conf file, you might also notice some commented-out sections (preceded by the ‘#’ character). These comments include several examples, so they’re worth a read.
How to Configure SNMP Community Strings in Windows
To configure an SNMP community string in Windows, follow the previous instructions to navigate to the SNMP Service Properties window for your OS version. From the Security tab, click the Add button to enter a new community string and choose the appropriate access rights – like Rear-only or Read-write.
Seven SNMP String Best Practices
When creating an SNMP community string, there are a few best practices to keep in mind:
- Use Long and Complex Strings: The longer the password is, the more difficult it is to guess.
- Avoid Common Words: Avoid using easily guessed words like “public” or “private.” Use a mix of letters, numbers, and symbols.
- Separate Read-Only and Read-Write Strings: Use different strings for read-only and read-write to avoid potential threats.
- Storing Securely: Store the string securely, and do not share it with others.
- Change Your Strings Regularly: Update your strings regularly to avoid risks.
- Restrict Access: Limit access to specific IP addresses or subnets.
- Monitor Usage: Regularly monitor SNMP access logs to detect unauthorized access attempts.
How to Confirm an SMMP Community String Is Working
The easiest way to confirm that an SNMP community string is to try to use it to manage the device. If the string is working, you should be able to view information about the device. If not, you’ll get an error message.
SNMP Monitoring With Domotz
You can use Domotz to monitor any SNMP (v1, v2, v3) OID values and configure thresholds for alerting on those sensors with our SNMP Monitoring feature.
SNMP Monitoring with Domotz will help you efficiently monitor and manage network devices using SNMP protocols. You can gather detailed data and insights from network devices, ensuring optimal performance and reliability.
Additionally, we offer pre-configured SNMP templates for popular devices, simplifying setup and saving time by providing instant access to key metrics without manual configuration.
Further, the SNMP MIB Browser allows you to explore and access device-specific MIBs (Management Information Bases), enabling advanced customization and monitoring for any SNMP-compatible device.
Leveraging Domotz, you can simplify network management and enhance your network’s security posture.
Further information about SNMP and SNMP monitoring:
