SNMPv3 basics

The SNMP protocol structure has changed significantly with version 3. SNMPv3 is now divided into a number of modules with clearly defined interfaces that communicate with one another. The three main elements in SNMPv3 are "Message Processing and Dispatch (MPD)", "User-based Security Model (USM)" and "View-based Access Control Mechanism (VACM)".

The MPD module is responsible for the processing and dispatch of inbound and outbound SNMP messages.
The USM module manages security features that ensure the authentication of the users and the encryption and integrity of the data. SNMPv3 introduced the principle of the "security model", so that the SNMP configuration in LCOS LX primarily uses the security model "SNMPv3". However, for compatibility reasons it may be necessary to also take the versions SNMPv2c or even SNMPv1 into account, and to select these as the "security model" accordingly.
VACM ensures that the sender of an SNMP request is entitled to receive the requested information. The associated access permissions are found in the following settings and parameters:
"SNMPv3-Views" collect together the content, status messages, and actions of the Management Information Base (MIB) that are permitted to receive or execute an SNMP request. These views can be single values, but also complete paths of the MIB. This content is specified by the OIDs of the MIB entries. In this way, a successfully authenticated sender of an SNMP request only has access to that data specified in the applicable SNMPv3 views.
"SNMPv3-Groups" collect users with the same permissions into a specific group.
"Security levels" relate to the exchange of SNMP messages. The following levels can be selected:
The SNMP request is valid without the use of specific authentication methods. Authentication merely requires the user to belong to an SNMP community (for SNMPv1 and SNMPv2c) or to specify a valid user name (for SNMPv3). Data transfer is not encrypted.
SNMP requests are only processed following authentication by means of the HMAC-MD5 or HMAC-SHA algorithm, but data transfer is not encrypted.
SNMP requests are only processed following authentication by means of the HMAC-MD5 or HMAC-SHA algorithm, and data transfer is encrypted by the DES or AES algorithm.
"Context" is used to distinguish the various SNMP entities.

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