View source for MFD:IF-MIB

{{MFDTutorial}}

== MFD: IF-MIB ==
'''NOTE: this tutorial is based on the code for the upcoming release
5.2 (currently in the main CVS line). If you generate code from a
release prior to 5.2, your results may vary.'''


This tutorial documents the process of implementing the
''IF-MIB'' MIB module for Linux. We'll start with the
''ifTable'', and then do the ''ifXTable''.
    
=== Introduction ===
    
The data for both of these tables comes from the kernel. This means
that we have to explicity ask for the data, the data may not be
in the format we would like it to be in, and all the data we want may
not be available. It also means that we will not be notified when the
data changes.

We cannot really do anything about the format of the data that we get
from the kernel. The ifXTable presents an additional twist, in that it
contains 64 bit counters for statistics, and the statistics available
for the Linux 2.4 kernels are only 32 bits. So we'll  cache data and
do periodic polls to maintaine these values.

As is often the case with external data, the interfaces data we get
from the kernel is not sorted by the index specified by the MIB. The
kernel reports data by interface names ('eth0', 'lo', etc), and the
''IF-MIB'' tables specifies an integer, ''ifIndex'', as
the table index.