CentOS use SNMP to show interface useage

Question

I have an SNMP monitoring box and want to monitor interface utilisation on a clustered database server. I'm trying to work out the correct OID to monitor - I just need SNMP to return the total interface throughput at a given time.

The SNMP box is already configured and will correctly graph it. All howtos I can find talk about setting up Catci or MRTG which is all well and good, but what I need seems simpler, yet I can't seem to find what I'm looking for. The SNMP box is already configured with the correct community name etc so this should be a really easy one in theory.

Any help very gratefully received

Thanks

Solution

When you say "interface utilisation", I assume you mean Ethernet interface utilization. If that assumption is correct, there are a couple OIDs to investigate:

• 1.3.6.1.2.1.2.2.1.10 - ifInOctets returns the total number of octets received on the interface, including framing characters.
• 1.3.6.1.2.1.2.2.1.16 - ifOutOctets returns the total number of octets transmitted out of the interface, including framing characters.
• 1.3.6.1.2.1.31.1.1.1.6 - ifHCInOctets returns the total number of octets received on the interface, including framing characters (this is the 64-bit version of ifInOctets).
• 1.3.6.1.2.1.31.1.1.1.10 - ifHCInOctets returns the total number of octets transmitted out of the interface, including framing characters (this is the 64-bit version of ifOutOctets).

Each OID is part of a table and will have an associated index that links it to an interface description (e.g., eth0 or br1).

These OIDs provide a count of octets received and transmitted so they require a little massaging to get into the utilization rates you desire. In the past when I've monitored these OIDs I've queried for two values a few seconds apart and then calculated the rate.

(QueryResult2 - QueryResult1) / (SecondsElapsed)

I would guess that Cacti (which I assume you're using since you tagged your question with it) has some way to calculate rates from SNMP values, however, I've never used it so I am not positive.

One other important note is that the default snmpd.conf included with CentOS may not have these OIDs enabled. If you run snmpwalk on 1.3.6.1.2.1.2 and 1.3.6.1.2.1.31 and receive empty results, edit /etc/snmpd.conf to configure the SNMP daemon to respond to those OIDs. I can't remember the exact syntax but I think adding a line like,

view   all   included   .1

will enable all available OIDs on the server.