Simple Network Management Protocol is widely used to gather information from network nodes. SNMP is an application layer protocol that runs on top of TCP/IP, typically on UDP port 161. SNMP is most often in read-only mode, in which information is read from the node, but no changes can be made. SNMP also supports read-write mode, which allows changes to be made to the node’s configuration.

There are three versions of SNMP, V1, V2 and V3. V1 and V2lack strong security methods. V3 supports strong security by enabling the use of MD5 or SHA hashed authentication and DES encryption with SNMP messages.

To configure SNMP V1

Router(config)#snmp-server community <string> ro <ACL> (Read-only string)
Router(config)#snmp-server community <string> rw <ACL> (Read-write string)

Simple SNMP V3 configuration:

Router(config)#snmp-server group SNMP_GROUP v3 auth
Router(config)#snmp-server user SNMP_USER SNMP_GROUP v3 auth md5 my_password