[mrtg] MaxBytes Question

Tyler, Rodney rtyler at gntc.edu
Wed Sep 4 17:05:05 CEST 2013


I'm new to MRTG and bandwidth monitoring, but I've been asked to setup traffic monitoring for a specific Ethernet interface on a Cisco Catalyst 6509 that connects two campuses over a fiber WAN link.  The third party fiber provider says they are giving us 100Mbps across the fiber, and we want to verify if we are getting that, as well as document our throughput historically.  I have managed to setup SNMP and MRTG and get successful connections, but I'm confused about the MaxBytes, AbsMax, and Unscaled.  As I said, the link speed is supposed to be 100Mbit/s (100Mbps).  But our interface is connected at 1000Mbps, as shown below from a partial "show interface" command:

  Hardware is C6k 1000Mb 802.3
  MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,
  Full-duplex, 1000Mb/s, media type is 10/100/1000BaseT
  Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 544000 bits/sec, 408 packets/sec
  5 minute output rate 5656000 bits/sec, 595 packets/sec
     554615327 packets input, 128091215313 bytes, 0 no buffer
     839477309 packets output, 1079159783816 bytes, 0 underruns

What should my MaxBytes be set to?  Is it supposed to reflect my 1Gbps interface speed or the 100Mbps link speed stated by the vendor?  Do I need to set the AbsMax and Unscaled keywords?  Also, what is the best way to "clear" the MRTG data collected thus far and start over?  My current graph looks like this:

[cid:image001.png at 01CEA95E.9C8A1C80]

Thank you for your help,

Rodney Tyler
rtyler at gntc.edu<mailto:rtyler at gntc.edu>

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