We're currently using the Cisco 1921/K9 router along with SG300 L3 switch and other L2 switches in the office environment. We're hooked up to a 10M fiber line for internet but not sure if we need that much bandwidth yet. What's a good way to test out if our current usage actually needs that much bandwidth?

My initial thoughts were to see how many times during the day we hit peak bandwidth usage. Is it possible to track that via the current equipment? Is this even a good method for testing bandwidth needs?

  • What firewall do you have? Cisco PIX/ASAs include utilization graphs. – generalnetworkerror Jun 9 '13 at 5:56
  • If you find out that you don't need all that capacity, what actions are you planning to take? Is the purpose to order smaller/cheaper circuit? – ytti Jun 9 '13 at 8:13
  • @generalnetworkerror no firewalls – lamp_scaler Jun 9 '13 at 9:31
  • @ytti based on the data, either up the bandwidth or down the bandwidth plan from our ISP – lamp_scaler Jun 9 '13 at 9:32
  • Can you post 'sh int X' for your WAN 10M interface (is the wan link itself 10M, or where is the actual 10M congestion point?). – ytti Jun 9 '13 at 9:46

Generally speaking you can install MRTG or any network graphing and historical data software which can pull interface statistics via SNMP. A nice and easy free software for this is CactiEZ. It can be easily run out of the box on an old server or mounted and installed easily on a VM.

However, since you're using a Cisco router, you can enable NetFlow on your interfaces and export that information to a Netflow collector/software such as Solarwinds Traffic Analyzer. This allows you to use the router to classify the types of traffic traversing that interface and report that back to the collector. You can then get better statistical information on what kind of traffic is being utilized and where its coming and going to as well.

  • Another excellent NF collector is Scrutinzer: plixer.com/Products/download-options.html. Free version has some limitations, but it's still very useful and it just answered a question I had earlier today about a 250Mb/s outbound spike. – generalnetworkerror Jun 9 '13 at 6:07
  • How does one enable netflow? does it cost extra? – lamp_scaler Jun 9 '13 at 9:32
  • @lamp_scaler - you could check plixer.com/Scrutinizer-Netflow-Sflow/…, but not sure if your router has the software feature. – generalnetworkerror Jun 9 '13 at 9:53
  • @lamp_scaler I don't believe you require any additional license for NetFlow on a 1900 series router. You should be able to enable it by adding, to each interface, ip flow egress ip flow ingress and in the global config....do an ip flow-export ? and configure destination, version, and source. – knotseh Jun 10 '13 at 14:29

SNMP is very handy for this type of monitoring. For just one router, you can download the free version of PRTG and set it up to monitor the interface's bandwidth.

On your router you are going to need to enable SNMP access. To do so, enter snmp-server community [name of your choice] RO in global-configuration mode. Setting up PRTG is quite simple as well, and there is plenty of documentation on their website regarding the specifics.

  • It's very hard with SNMP to see actual peak-rate, as it's averaged data. Optimally we'd see all data send with at least millisecond precision or greater, then we could calculate peak-demand. – ytti Jun 9 '13 at 8:14
  • @ytti yes, but if you aren't hitting your peak consistently over time, then you may not need all the extra bandwidth. If you hit 20Mbps for a few seconds, but average 2Mbps, the peak is not characteristic of your traffic flow and overall link saturation. – Yosef Gunsburg Jun 9 '13 at 9:24
  • If you hit 20Mbps for few seconds, and you downgrade link to 2Mbps, you'll be dropping frames at those few seconds. And you'll experience high latency in other smaller peaks. – ytti Jun 9 '13 at 9:25
  • @ytti say you have a user downloading a 100MB file. It will peak during the download, but will not drop frames if you scale the link down. With less bandwidth, the L4 protocols will take care of those issues with windowing. – Yosef Gunsburg Jun 9 '13 at 9:29
  • Only way to scale down the transfer is to drop frames, that is how TCP works :) – ytti Jun 9 '13 at 9:32

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