[mrtg] Re: Gigabit speed, net-snmp, and overflows

Dawn Keenan dkeenan at ist.uwaterloo.ca
Fri Feb 10 16:17:39 MET 2006

John Haggerty wrote:
> I'm trying to track Gigabit traffic on Red Hat 3 Update 5 servers with 
> net-snmp (rpm net-snmp-5.0.9-2.30E.15) with mrtg (rpm 
> mrtg-2.10.15-1.i386), but even though I've reduced the polling time to 1 
> minute, at the highest speeds, the results are inaccurate, I suppose 
> because the 32 bit counters overflow in around 30 seconds.
> I cannot see how to configure net-snmp to serve up the 64 bit high speed 
> counters; for example, cfgmaker says

You probably need a more recent version of Net-SNMP built with 
"--enable-mfd-rewrites" to get the IfXTable 64 bit counters for interfaces.

 From http://www.net-snmp.org/about/ChangeLog.html (for Net-SNMP 5.2):

  - new experimental tables/rewrites for Linux, including:
       ifTable, ifXTable, inetCidrRouteTable, ipCidrRouteTable,
       ipAddressTable, ipSystemStatsTable, ipNetToPhysicalTable.
    - Enable these talbles by specifying --enable-mfd-rewrites to configure.
    - Most of these tables have IPv6 support as well.
  - ifIndex no longer changes when interfaces are added/removed, and all
     tables/object wiil now use the same ifIndex for the same interface.


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