Monitoring bandwidth consumption

I have a 1700 series Cisco router and a 512K bit/sec leased line. About 50 users are accessing the Internet through that router, and I want to monitor my bandwidth consumption through the router. Is there any way by which I can monitor bandwidth (tool or software)?
- Amit Goswami

My favorite tool for this type of task is MRTG. It is essentially a Perl script, so you can have it running on just about any platform. There is a little bit of housekeeping that needs to be done before you start turning things on. You will need to enable SNMP on your Cisco router. If you enable it on both the Ethernet and serial port (assuming you are using an external DSU/CSU), you can watch both sides of the router and potentially see problems on both sides. Especially if you enable SNMP on the serial interface of the router, I would strongly encourage the use of a read-only community string so the likelihood of someone compromising the router are minimized. Another benefit to this option is if you put all your users on a "managed" router (one that supports SNMP), you can also watch your users' network usage on each port and tell to a degree who is hogging the connection.

The implementations of MRTG that I have done have been on Windows. What I will outline here will mostly apply to that and to other platforms such as Linux to varying degrees. You will need to have Perl installed so the scripts associated with MRTG can run. I use the ActivePerl distribution of Perl. Once this is installed, you will need to set up either IIS or Apache on the server you're using. Remember the directory for which the Web server software is set up. That will be needed for when you run the scripts to create the files used by MRTG so it can create them in the proper directory.

Before getting too gung-ho on getting things running, spend some time and thoroughly review the manual for MRTG so you use the correct options for your particular setup. Subscribe to the MRTG listserv so you will know when a new version comes out and avoid problems others have run into. If you have more than one SNMP device you will be monitoring, it would be a good idea to create a separate directory for each device on the Web server to keep the files separated and easier to deal with.

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