Essential SNMP

Appendix A. Using Input and Output Octets

To be SNMP-compatible, an IP device must support MIB-II (iso.org.dod.internet.mgmt.mib-2) objects. MIB-II contains the interfaces table (mib-2.interfaces.ifTable.ifEntry), which is one of the most useful objects for network monitoring. This table contains information about the system’s network interfaces. Some of its objects are:

ifDescr

A user-provided description of the interface

ifType

The interface’s type (token ring, Ethernet, etc.)

ifOperStatus

Whether the interface is up, down, or in some kind of test mode

ifMtu

The size of the largest packet that can be sent over the interface

ifSpeed

The maximum bandwidth of the interface

ifPhysAddress

The low-level (hardware) address of the interface

ifInOctets

The number of octets received by the interface

ifOutOctets

The number of octets sent by the interface

We explored various parts of this table in other chapters, but avoided saying too much about ifInOctets and ifOutOctets. RFC 1213 states that ifOutOctets and ifInOctets are the total number of octets sent and received on an interface, including framing characters.

In many environments, this information is crucial. Companies such as Internet service providers (ISPs) make their livelihoods by providing usable bandwidth to their customers, and thus spend huge amounts of time and money monitoring and measuring their interfaces, circuits, etc. When these pipes fill up or get clogged, customers get upset. So the big question is, how ...