B and an instance must be added to this. Particular object instances are important as they are real components of the device, whereas an OID is merely an identifier. For non-tabular or "scalar" objects the instance number is 0, for example, "sysDescr.0". For tabular objects, the instance is defined by the MIB and is a sequence of one or more variables, for example, "ifInOctets.2", as mentioned above, or "tcpConnState.179.74.15.126.1192.225.226. 126.197.80" where "tcpConnState" means TCP connection state. Rather than specifying the instance number, one can also use get-next while specifying only the OID from the MIB, such as sysDescr. This will provide the first instance of that type from the SNMP agent. This method can be used for all types of managed object. When using an MIB browser, the user selects the MIB node of interest and then selects get-next. Alternatively, the user selects an MIB node, explicitly enters the instance in which they are interested after the end of the OID and uses get. The AdventNet SNMP MibBrowser allows loading of MIBs, MIB browsing, walk- ing through the MIB tree, searching MIBs and all other common SNMP-related functions. The hierarchical structure of some MIB databases gives them a tree structure which an operator can find it convenient to walk through to check the sta- tus of various managed objects. The data that are available through an SNMP agent in a managed device can be viewed and manipulated through the MibBrowser. Figure 4.3 shows the main window of the MibBrowser. The operations that can be performed using the MibBrowser are available in the toolbar. The left pane has the MIB tree, which is a structure through which all MIBs that are loaded can be viewed. The MIB tree component enables the user to traverse the tree, view the loaded MIBs and see the definition for each node. The right pane has labeled text fields to specify basic parameters such as Host and Community and it has a Result text display area in which to view results of requests sent to the managed object. In ad