Installation and configuration of net-snmp agent on CentOS Linux.

SNMP v3 is the version of Simple Network Management Protocol with advance security mechanism to handle SNMP packets. The net-snmp agent is free snmp v3 agent. The version 3 of Simple Network Management Protocol provides more secure authentication and cryptographic features. The snmpv3 defined in RFCs 3413 and 3414. The steps presented below related to CentOS Linux.
Installation:

# yum install net-snmp

Start snmp service and check its status:

# systemctl start snmpd.service
# systemctl status snmpd.service
● snmpd.service - Simple Network Management Protocol (SNMP) Daemon.
Loaded: loaded (/usr/lib/systemd/system/snmpd.service; disabled; vendor preset: disabled)
Active: active (running) since Sun 2018-04-01 17:53:11 EDT; 1s ago
Main PID: 5173 (snmpd)
CGroup: /system.slice/snmpd.service
└─5173 /usr/sbin/snmpd -LS0-6d -f

Install snmp utilities:

# yum install net-snmp-utils

Stop snmp service:

# systemctl stop snmpd.service

Add snmp user, configure authentification method and encryption:

# net-snmp-create-v3-user -A shapassword1 -a SHA -X AES -x aespassword1 v3snmpuser1

Start snmp service:

# systemctl start snmpd.service

Verify how it works locally:

# snmpwalk -v 3 -a SHA -A shapassword1 -l authPriv -x AES -X aespassword1 -u v3snmpuser1 127.0.0.1

Verify how it works remotely:

# snmpwalk -v 3 -a SHA -A shapassword1 -l authPriv -x AES -X aespassword1 -u v3snmpuser1 192.168.2.1

If it does not work remotely but works locally check if it is firewall issue. Stop firewall:

# systemctl stop firewalld.service

and repeat remote snmpwalk test. If it is working now it means that it is firewall problem and we need to configure firewall to allow remote snmp requests.
In /etc/firewalld/services directory create the snmp.xml file with following content:



SNMP
SNMP protocol

Start firewall and execute the firewall configuration commands:

# systemctl start firewalld.service
# firewall-cmd --reload
# firewall-cmd --zone=public --add-service snmp --permanent
# firewall-cmd --reload


Start snmpwalk from remotely to verify how it work now.