This is rather silly, but I lost some time with it, so I thought to put it in a blog post as it might be useful to others. Ok, a few days ago I took over an existing cacti installation; I was working to improve it and bring in some other stuff I always do in a cacti installation (note to self, I should really put some blog posts about cacti templates I use, as that will definitely save me some time in the future). One problem I noticed was that there was a traffic interface graph that was wrong when it was going over 114Mbps. I knew what the problem was and it should have been a quick fix.
All I had to do was to change from regular 32-bit counters to 64-bit counters and increase the maximum value to 1M. I have done that, but to my surprise the graph stopped working completely for the respective interface. So I had to dig into it, and debug the problem. I was able to see that the cacti poller snmp query was failing and returning:
1 2 3
That was strange, as I knew for sure a similar cisco switch works just fine with 64-bit counters (btw this was a C2960G). Running the snmp query by hand, like:
was working just fine and returning the counter. Finally after wasting some time I realized what was the problem: the host device was configured in cacti to use SNMPv1, and I only had to change this to SNMPv2 to make it work as expected. Hopefully this will help others in similar situations…
Conclusion: if your 64-bit snmp counters are not working as expected, be sure to check if you are using SNMPv2 or not. That might be your problem, as SNMPv1 doesn’t support that.