snmp v3安全級別有三種，分別為noAuthNoPriv（不認證也不加密）、authNoPriv（認證但是不加密）、authPriv（既認證又加密）
一、SNMPv3配置代碼：
snmp-server contact zhangsan snmp-server location chengdu snmp-server view MIB-2 mib-2 included
1）如果設置安全級別為authPriv
snmp-server group READONLY v3 priv read MIB-2 snmp-server user admin READONLY v3 auth sha mypass123 priv aes 128 myaes123
2）如果設置安全級別為authNoPriv
snmp-server group READONLY v3 auth read MIB-2 snmp-server user admin READONLY v3 auth sha mypass123
3）如果設置安全級別為noAuthNoPriv
snmp-server group READONLY v3 noauth read MIB-2 snmp-server user admin READONLY v3
注意：上述密碼設置長度必須大於等於八位，否則在linux上使用snmpwalk命令時，會報錯提示
Error: passphrase chosen is below the length requirements of the USM (min=8). snmpwalk: (The supplied password length is too short.) Error generating a key (Ku) from the supplied privacy pass phrase.
其中sha可改成md5，
md5 Use HMAC MD5 algorithm for authentication sha Use HMAC SHA algorithm for authentication
aes可改成：3des，des。
3des Use 168 bit 3DES algorithm for encryption aes Use AES algorithm for encryption des Use 56 bit DES algorithm for encryption
2、snmpwalk獲取信息命令
1）安全級別為authPriv時，snmpwalk獲取信息方式：
snmpwalk -v 3 -u admin -l authPriv -a sha -A mypass123 -x aes -X myaes123 192.168.0.80 ".1.3.6.1.2.1"
2）安全級別為authNoPriv時，snmpwalk獲取信息方式：
snmpwalk -v 3 -u admin -l authNoPriv -a sha -A mypass123 192.168.0.80 ".1.3.6.1.2.1"
3）安全級別為noAuthNoPriv時，snmpwalk獲取信息方式：
snmpwalk -v 3 -u admin -l noAuthNoPriv 192.168.0.80 ".1.3.6.1.2.1" snmp-server contact zhangsan snmp-server location chengdu snmp-server view MIB-2 mib-2 included
1）如果設置安全級別為authPriv
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