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I have MRTG with RRDTool configured to monitor the bandwidth on a switch, it is set to measure the traffic in bits. For the interface I need monitored it is showing this:

Description: GigabitEthernet2/0/25 ifType: ethernetCsmacd (6) ifName: Gi2/0/25 Max Speed: 1000.0 Mbits/s

Which is correct, it is a gigabit switch. However, on the graph it is showing 84.938Mbps out, which is not accurate, it is more like 849.38Mbps.

How do I get it to display the proper values?

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up vote 2 down vote accepted

This is counter rollover. Make sure you are using SNMPv2(SNMP v2 use 64-bit counters).

Add :::::2 to switch definition(Target[myswitch]: 2:public@switch1:::::2) and enable SNMP v2 on switch.

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Thank you, after reading your answer, I have found documentation to support this. Is it possible to get the proper values with snmp v1 (uses 32-bit counters?). The issue is that the switch is only snmp v1 capable with the current firmware. – SuperMicro321 Feb 5 '11 at 12:59
32-bit = 1024*1024*1024*4 = 1Gbit * 4s. You can set interval 4 second(0:4) and initial creation database, but I think it will not work. – alvosu Feb 5 '11 at 13:20

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