Cisco SRST User Guide - Page 47

Chapter 1 Cisco SRST SNMP MIB Support CISCO-SRST-MIB Object Groups For example, the Interface MIB (RFC 1573) has a key table called the ifTable. Its index object is ifIndex, an integer. Minus the instance, the OID for a counter from that table is: iso.internet.mgmt.mib-2.interfaces.ifTable.ifEntry.ifInOctets Or, numerically: 1.3.6.1.2.1.2.2.1.10 For the interface with ifIndex 7, the full OID is: iso.internet.mgmt.mib-2.interfaces.ifTable.ifEntry.ifInOctets.7 1.3.6.1.2.1.2.2.1.10.7 Observe that row selection (instance) comes after column selection. This can be particularly confusing when you are applying the principle of lexical order to a table. Using the GetNext protocol operation to walk a table, you can proceed by column, that is, all instances for a column are returned before the next column is started. Table indexes can be much more complex than tables. Here is an example from the Cisco VINES MIB. The INDEX clause from the ASN.1 definition is: INDEX { cvForwNeighborHost, ifIndex, cvForwNeighborPhysAddress } The first two indexes are simple integers, with ifIndex being imported from the standard ifTable. The final index is a variable length octet string. Including the integers is simple and obvious. The variable-length index object gets more complex. RFC 1212 includes rules for encoding variable length index objects as instances. The general rule is that the value is preceded by a length, and the length and each part of the value are separate subidentifiers. So, for example, if we have neighbor host number 9, ifIndex 3, and an Ethernet neighbor physical address 0000.0c03.1ef0, the instance portion of an object for that row is 9.3.6.0.0.12.3.30.240. In RFC 1902, SNMPv2 extends the instance encoding rules to include an "IMPLIED" keyword that can be used on the final instance object if it is variable length. When "IMPLIED" is present, the string instance cannot have a zero length in front of it. Because lexical ordering for variable length instance objects effectively sorts them by length, your ASCII text index will not come out naturally in alphabetical order. CISCO-SRST-MIB Object Groups Table 1-6 lists the CISCO-SRST-MIB objects, which are presented according to their group. The CISCO-SRST-MIB is organized by the following groups listed in Table 1-6 • csrstConf • csrstNotifInfo • csrstActiveStats • csrstSipConf • CiscoSrstMIBNotifs OL-7959-01 Cisco SRST SNMP MIB Release 3.4 Guide 1-33