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Definition 3-2. The Ethernet Statistics table from RFC 1757
-- The Ethernet Statistics Group -- -- Implementation of the Ethernet Statistics group is -- optional. -- -- The Ethernet Statistics group contains statistics -- measured by the probe for each monitored interface on -- this device. These statistics take the form of free -- running counters that start from zero when a valid entry -- is created. -- -- This group currently has statistics defined only for -- Ethernet interfaces. Each etherStatsEntry contains -- statistics for one Ethernet interface. The probe must -- create one etherStats entry for each monitored Ethernet -- interface on the device. etherStatsTable OBJECT-TYPE SYNTAX SEQUENCE OF EtherStatsEntry ACCESS not-accessible STATUS mandatory DESCRIPTION A list of Ethernet statistics entries. ::= { statistics 1 } The object name (or table name) etherStatsTable begins with a lowercase letter, indicating a Value (see Section 2.3.4). The) associated syntax definition is a sequence of the EtherStatsEntry, which begins with an uppercase letter to indicate a Type. This object is nonaccessible because it is a table. The status is mandatory, meaning all implementations must support this object. A description of the object is A list of Ethernet statistics entries. The { statistics 1 } designation indicates that this table is the first subtree under the statistics group. etherStatsEntry OBJECT-TYPE SYNTAX EtherStatsEntry ACCESS not-accessible STATUS mandatory DESCRIPTION A collection of statistics kept for a particular Ethernet interface. As an example, an instance of the etherStatsPkts object might be named etherStatsPkts.1 INDEX { etherStatsIndex } ::= { etherStatsTable 1 } The object value (etherStatsEntry) ends with Entry. This identifies a table row object. The index clause specifies the columns within each row that form the table. This object is the first object under the etherStatsTable subtree. EtherStatsEntry ::= SEQUENCE { etherStatsIndex INTEGER (1..65535), etherStatsDataSource OBJECT IDENTIFIER, etherStatsDropEvents Counter, etherStatsOctets Counter, etherStatsPkts Counter, etherStatsBroadcastPkts Counter, etherStatsMulticastPkts Counter, etherStatsCRCAlignErrors Counter, etherStatsUndersizePkts Counter, etherStatsOversizePkts Counter, etherStatsFragments Counter, etherStatsJabbers Counter, etherStatsCollisions Counter, etherStatsPkts64Octets Counter, etherStatsPkts65to127Octets Counter, etherStatsPkts128to255Octets Counter, etherStatsPkts256to511Octets Counter, etherStatsPkts512to1023Octets Counter, etherStatsPkts1024to1518Octets Counter, etherStatsOwner OwnerString, etherStatsStatus EntryStatus } The syntax of the etherStatsTable is a sequence of EtherStatsEntry. The sequence contains 21 objects that will make up the columns of each row. etherStatsIndex OBJECT-TYPE SYNTAX INTEGER (1..65535) ACCESS read-only STATUS mandatory DESCRIPTION The value of this object uniquely identifies this etherStats entry. ::= { etherStatsEntry 1 } The etherStatsIndex object may take on a value between 1 and 65,545. This index determines how the various objects will be retrieved.
Managed objects are arranged into groups for two reasons. First, a logical grouping facilitates the use of the object identifiers and tree structure discussed in Section 3.1. Second, it makes the SNMP agent design more straightforward because the implementation of a group implies the implementation of all objects within the group. Thus, both the software developer and the end user can clearly understand a statement of support for, say, the TCP Group.
The next sections discuss the Internet standard MIB-I (RFC 1156) and MIB-II (RFC 1213) managed objects. MIB-I contained 114 objects. MIB-II, which is backward-compatible with MIB-I, contains these 114 objects plus 57 more, for a total of 171 objects. Chris VandenBergs article [3-5] discusses the MIB-II enhancements. Appendix G details the various objects.
The System group provides a textual description of the entity in printable ASCII characters. This text includes a system description, OID, the length of time since the reinitialization of its network management entity, and other administrative details. Implementation of the System group is mandatory. The OID tree for the System group is designated {1.3.6.1.2.1.1}, as shown in Figure 3-2.
Figure 3-2. The System group
The Interfaces group {1.3.6.1.2.1.2} provides information about the hardware interfaces on a managed device, as shown in Figure 3-3. This information is presented in a table. The first object (ifNumber) indicates the number of interfaces on the device. For each interface, a row entry is made into the table, with 22 column entries per row. The column entries provide information about the interfaces, such as the interface speed, physical (hardware) address, current operational state, and packet statistics.
Figure 3-3. The Interfaces group
MIB-I included the Address Translation group, shown in Figure 3-4, but it was deprecated in MIB-II. The deprecated status means that MIB-II includes the Address Translation group for compatibility with MIB-I, but will probably exclude it from future MIB releases. The Address Translation group provided a table that translated between IP addresses and physical (hardware) addresses. In MIB-II and future releases, each protocol group will contain its own translation tables. The Address Translation group is designated {1.3.6.1.2.1.3}. It contains one table with three columns per row.
Figure 3-4. The Address Translation group
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