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SNMP, or Simple Network Management Protocol, is widely used to communicate with and monitor network devices, servers, and more, all via IP. In the previous article, we installed an SNMP agent on a CentOS 6.5 server. This agent allows for the collection of data from our server and makes the information available to a remote SNMP manager. To add a little security, we'll now change the port that SNMP listens on.

Change SNMP Port

Preflight Check

  • These instructions are intended for changing the SNMP port.
  • I’ll be working from a Liquid Web Core Managed CentOS 6.5 server, and I'll be logged in as root.
  • SNMP is installed and configured per the tutorial on How To Install and Configure SNMP on CentOS.

Change the SNMP Port

First, echo a new configuration into the SNMP configuration file:

echo OPTIONS=\"-LS0-5d -Lf /dev/null -p /var/run/snmpd.pid -x TCP:13371 UDP:13371\" >> /etc/sysconfig/snmpd

-LS0-5d specifies the logging level. In this case levels 0 through 5 will be logged; log levels are defined as follows:

0 or ! for LOG_EMERG,
1 or a for LOG_ALERT,
2 or c for LOG_CRIT,
3 or e for LOG_ERR,
4 or w for LOG_WARNING,
5 or n for LOG_NOTICE,
6 or i for LOG_INFO, and
7 or d for LOG_DEBUG.

-p /var/run/snmpd.pid saves the process ID of the daemon into /var/run/snmpd.pid.

-x TCP:13371 UDP:13371 listens on port 13371 (TCP and UDP) on all IPv4 interfaces. Port 13371 was used specifically for this tutorial, and can be replaced with a custom report number.

Now, restart the SNMP service to reload the new configuration file:

service snmpd restart

Test the SNMP Configuration

To verify that SNMP is now listening on the correct port use the following command:

netstat -lnp | grep snmp

Let's test the SNMP configuration... try running the following two commands:

snmpwalk -v 2c -c idv90we3rnov90wer -O e

Note: idv90we3rnov90wer is the "community" used in the previous tutorial; your community string will likely be different. If you're going to connect to SNMP from a remote server, be sure your server's firewall has the appropriate ports open
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About the Author: Justin Palmer

Justin Palmer is a professional application developer with Liquid Web

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