Overview
SNMP stands for “Simple
Network Management Protocol”, it can be utilized to monitor any devices that
support snmp, few of the devices are server, router, network printers,
firewalls. SNMP can monitor a variety of parameters for these devices such as
server performance, network usage, disk utilization.
Applies To
Tested on RHEL 7, CentOS 7, though it can be configured on
most of the *nix flavor of OS.
Pre-Requisites
·
snmp,
snmp-utils
Installation and Configuration procedure
First of all, we will check if the package is already
installed else we will install the packages.
Check Package
Check if the package is already installed, to check package
installation status, run the command;
rpm -qa | grep net-snmp
net-snmp-utils
Install Package
After checking the package installation status, if the
package is not installed. Install the package to install run the command;
yum install net-snmp
net-snmp-utils -y
Verify Installation
After installing the net-snmp packages verify if the package
is installed, to check package installation status, run the command;
rpm -qa | grep net-snmp*
SNMP – Configuration File
Default configuration file that is configured as per the
below. To display current configuration without comments and lines non-blank
lines, run command;
grep -v "^$"
/etc/snmp/snmpd.conf | grep -v '^ *#'
Default Configuration File – Snippet
com2sec notConfigUser
default public
group notConfigGroup v1 notConfigUser
group notConfigGroup v2c notConfigUser
view systemview included
.1.3.6.1.2.1.1
view systemview included
.1.3.6.1.2.1.25.1.1
access notConfigGroup
"" any noauth
exact systemview none none
syslocation Unknown (edit /etc/snmp/snmpd.conf)
syscontact Root <root@localhost> (configure
/etc/snmp/snmp.local.conf)
dontLogTCPWrappersConnects yes
Firewall Configuration
SNMP protocol works on UDP port “161” and this port needs to be opened in order to listen and scan
the report from remote servers and for latest version of snmp service supports
running on TCP port which is again on “161”.
Firewall Configuration – Open UDP Port
After installing and checking the default configuration, the
next step that needs to be done is to open firewall port, snmp protocol run on
UDP port 161.
firewall-cmd --permanent
--add-port=161/udp
Firewall Configuration – Reload
Reload the firewall configuration.
firewall-cmd --reload
Firewall Configuration – List
After reloading firewall daemon, list the current rules set.
firewall-cmd --list-alll
snmpwalk – localhost Query
After configuring the firewall, you can go ahead and test
the snmp query data on the localhost it should be able to retrieve the OID
values when you run. To retrieve the information run the command;
snmpwalk -v 1 -c public -O e
127.0.0.1
snmpwalk – Remote Query
To query from a remote client to retrieve the OID values
when you run. To retrieve the information run the command; in this case we are
querying from a windows machine.
snmpwalk -r:54.165.245.172 -q
-c:public
SNMP Configuration
In order to SNMP to work for any query requests, it should be configured only agentaddress directives is listed and configured, similarly other directives can be configured according to the business needs.
Listening address
This attribute will associate the IP address wherein the
snmp service will listen on.
Attribute Name
|
IP Address Information
|
Port
|
agentaddress
|
127.0.0.1
|
161
|
agentaddress
|
IP Address
|
161
|
agentaddress
127.0.0.1:161
SNMP Daemon Management
State
|
Command
|
Purpose
|
Enable
|
systemctl enable snmpd
|
Enable the service to start at boot and start
automatically
|
Start
|
systemctl start snmpd
|
Start the service
|
Stop
|
systemctl stop snmpd
|
Stop the service
|
Restart
|
systemctl restart snmpd
|
Restart the service
|
Disable
|
systemctl disable snmpd
|
Disable the service to start at upon booting
|
Mask
|
systemctl mask snmpd
|
Troubleshooting
Timeout: No Response from 127.0.0.1
Error Message
Timeout: No Response from 127.0.0.1
Cause
One of the cause is the service is not running, start the
service.
Another cause is when the remote server doesn’t have port is
blocked or not listening default port on the client.
systemctl status snmpd
Resolution
To resolve the issue we will start the daemon and query
again for the first cause, for the second cause ensure firewall port is configured such that UDP port 161 is opened and listening, check firewall configuration section.
systemctl start snmpd
SNMP Version Features
SNMP has 3 versions currently, that can be configured based
on the business needs. The below table will give insight into different
versions and its features that provide
device statistics.
SNMP
Version
|
Features
|
Version 1
|
This provides device statistics and error reporting
without consuming a lot of system resources. Security was limited to
community strings and access controls based on the IP address of the querying
server. Data communication wasn't encrypted.
|
Version 2
|
This is referred to as v2c
which expanded the number of supported error codes, increased the size of
counters used to track data, and has the ability to do bulk queries that more
efficiently loaded response packets with data
|
Version 3
|
This version provides greater security and remote
configuration capabilities than earlier versions.
Access is not only limited to a single community
string for read-only and read/write access, as usernames and passwords can
also be configured in this version.
Support for
encrypted SNMP data transfer and transfer error detection is also provided.
|
Just what I needed. Thanks :-)
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