Cisco 2950G 24 Software Configuration Guide - Page 479

Chapter 24 Configuring SNMP Understanding SNMP Table 24-1 SNMP Security Models and Levels Model SNMPv1 SNMPv2C SNMPv3 SNMPv3 Level noAuthNoPriv noAuthNoPriv noAuthNoPriv authNoPriv Authentication Encryption Community string No Community string No Username No MD5 or SHA No Result Uses a community string match for authentication. Uses a community string match for authentication. Uses a username match for authentication. Provides authentication based on the HMAC-MD5 or HMAC-SHA algorithms. You must configure the SNMP agent to use the SNMP version supported by the management station. Because an agent can communicate with multiple managers, you can configure the software to support communications with one management station using the SNMPv1 protocol, one using the SNMPv2C protocol and another using SNMPv3. SNMP Manager Functions The SNMP manager uses information in the MIB to perform the operations described in Table 24-2. Table 24-2 SNMP Operations Operation Description get-request get-next-request get-bulk-request2 Retrieves a value from a specific variable. Retrieves a value from a variable within a table.1 Retrieves large blocks of data, such as multiple rows in a table, that would otherwise require the transmission of many small blocks of data. get-response Replies to a get-request, get-next-request, and set-request sent by an NMS. set-request Stores a value in a specific variable. trap An unsolicited message sent by an SNMP agent to an SNMP manager when some event has occurred. 1. With this operation, an SNMP manager does not need to know the exact variable name. A sequential search is performed to find the needed variable from within a table. 2. The get-bulk command only works with SNMPv2 or later. SNMP Agent Functions The SNMP agent responds to SNMP manager requests as follows: • Get a MIB variable-The SNMP agent begins this function in response to a request from the NMS. The agent retrieves the value of the requested MIB variable and responds to the NMS with that value. • Set a MIB variable-The SNMP agent begins this function in response to a message from the NMS. The SNMP agent changes the value of the MIB variable to the value requested by the NMS. The SNMP agent also sends unsolicited trap messages to notify an NMS that a significant event has occurred on the agent. Examples of trap conditions include, but are not limited to, when a port or module goes up or down, when spanning-tree topology changes occur, and when authentication failures occur. 78-14982-01 Catalyst 2950 Desktop Switch Software Configuration Guide 24-3