How do I find out the SNMP OID prefix?

Question

I am trying to get information on the current IN / OUT bound traffic on an Airport Express router displayed in an openHAB setup.

what I need is to be able to supply a line something like these:

in:   snmp="<[192.168.2.111:public:.1.3.6.1.2.1.2.2.1.10.10:10000]"
out:  snmp=">[OFF:192.168.2.111:private:.1.3.6.1.4.1.4526.11.16.1.1.1.3.1.2:2]"
trap: snmp="<[192.168.2.111:public:.1.3.6.1.2.1.2.2.1.10.10:0]"

for my config file (see https://github.com/openhab/openhab/wiki/Snmp-Binding). I've got mrtg set up to get data from the Airport Express before, so SNMP is activated and working. No problem there.

However, I know nothing about SNMP really and cannot figure out how/where to find out what would pull current trafic load on eth0 from the router.

I appreciate any help I can get on this.

Answer 1

I solved it myself, using the excellent MIB Browser and SNMPmon apps (iPad). Broswing down the strukture, there is an IF-MiB:ifInOctets.1 (1 being because I am only interested in eth0) which makes me able to monitor the (inbound) octets being processed. There is also a ifOutOctets of course.

A description of the ifInOctets.1 OID

This page Description of bandwidth calculation describes how the octet counts can then be converted to network usage. In essence,

usage= D_ifInOctets*8*100/(T*ifSpeed) 

where D_ifInOctets is the difference in ontet counts (they are given as counts) between two points in time, T is the time elasped between the two pollina periods and ifSpeed is extracted from another note in IF-MiB.

For combined duplex bandwith usage. please have a look at the cisco docs resered to above.