For SNMP to operate, the NMS must have access to the MIB. To ensure that access requests are valid, some form of authentication must be in place.

SNMPv1 and SNMPv2c use community strings that control access to the MIB. Community strings are plaintext passwords. SNMP community strings authenticate access to MIB objects.

There are two types of community strings:

To view or set MIB variables, the user must specify the appropriate community string for read or write access. Play the animation in the figure to view how SNMP operates with the community string.

Note: Plaintext passwords are not considered a security mechanism. This is because plaintext passwords are highly vulnerable to man-in-the-middle attacks, in which they are compromised through the capture of packets.