Measuring T1 usagewith MRTG

John Abreau john.abreau at
Thu Aug 31 17:53:21 EDT 2006

I set up MRTG the other day, and I have it monitoring the two ports on
my PIX firewall and each port on my two Cisco switches. I don't have
access to the external router, which is owned and managed by my ISP.
I'm putting in a support call to ask them for SNMP access so I can
point MRTG at it.

In the meantime, I'm assuming that the statistics for the switch port
that the router is connected to is an accurate reflection of the
traffic through the router. MRTG is showing the following:

     Max  In: 778.9 kb/s (7.8%)
     Average  In: 92.5 kb/s (0.9%)
     Current  In:  	81.6 kb/s (0.8%)

     Max  Out: 1200.8 kb/s (12.0%)
     Average  Out: 74.1 kb/s (0.7%)
     Current  Out: 37.6 kb/s (0.4%)

We have a single T1 connection, which provides 1.44 Mbps of bandwidth.
If I'm interpreting this correctly, we're currently using about
26% of the T1's bandwidth and averaging 51%, with today's peak usage
coming in at 83% of the T1's capacity.

Am I interpreting this correctly? Also, I imagine there's a certain
amount of overhead in a T1, and I'm not sure how much that would be.
Would the figure above of 1200 Kbps Max Outbound indicate that our T1
was completely saturated at that point?

John Abreau
IT Manager
Zuken USA
238 Littleton Rd., Suite 100
Westford, MA 01886
T: 978-392-1777            F: 978-692-4725
M: 978-764-8934
E: John.Abreau at  W:

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