Interpreting bandwidth usage by MRTG/CACTI

155 pts.
Tags:
Bandwidth
Cacti
MRTG
Network monitoring
Hello guys. We have a dedicated lease line of 1 E1 (2Mbps) that we subscribe from an ISP. For the past several months, we have noticed that internet connection is so slow and it keeps us thinking if we are getting what we are paying for. I need help in interpreting an MRTG graph from CACTI of our E1 line if we are getting the appropriate bandwidth that is due us. Your interpretations and advices are most welcome.

Answer Wiki

Thanks. We'll let you know when a new response is added.

The MRTG graph will probably only show what you were using, not the capacity of the circuit.

If it hits the 2Mb level, then you got 2Mb at that time. Try one of the online speed testers, like speedtest.net, when no-one else is using it, which should give you an idea if the line is truly 2Mb. It also depends on how the router is configured, as to whether you really have 2Mb or there are some signalling as well that takes out a 64kbps slot. So it could be a bit less, legitimately.

If you have a Cisco router on the end, that can tell you how loaded the line is, and the speed it is set to be. That may also give an indication.

Just realized you posted the graph below. I would say from that graph, that you are getting 2Mb/s. You are unlikely to generate it all the time, but you can see that it hits this level quite a bit, so it looks OK from that picture.

Sometimes you just have to trust the ISP!

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  • JuneC
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  • JuneC
    Thanks for the response. Admittedly, the MRTG reached the 2Mbps mark if we would consider the outbound traffic. However, the inbound says otherwise, it couldn't even hit the 0.5 Mbps mark. I would interpret this as a shortcoming on the ISP side of providing quality service to the client. They may give the client a 2Mbps mark on the outgoing traffice since they control their own routers but when it comes to inbound traffic, which is supposed to be the data coming from the internet/ world wide web, they seem to limit it to a minimal. I'm not really quite sure if what I just said is absolutely correct, they are just my own interpretations. Please make your own expert advices and interpretations and if you have the same experience, pls share it with us. Thank you.
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  • petkoa
    Hi JuneC MRTG can graph anything, but usually graphs the traffic on an interface - the main term is interface. So, if this graph is for the router at your site, then it is as you state: your inbound traffic is ~150Kbit/s; if, however, this is graph from the ISP's router interface connecting to your site, then things are opposite - your inbound traffic is ~2Mbit/s. See, for that interface outbound is in your direction, i.e. inbound for you. How many PCs in your LAN are using this internet connection and how? Nowdays 2Mbit/s are barely enough for a single home PC... Good luck, Petko A.
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