[mrtg] cablemodem questions

Jake Colman colman at ppllc.com
Wed Nov 20 17:39:15 MET 2002

My cablemodem is docsis-compliant so cfgmaker is able to produce an
intelligent config for it.

An snmpwalk shows that there are 4 interfaces:

interfaces.ifTable.ifEntry.ifDescr.1 = enet0
interfaces.ifTable.ifEntry.ifDescr.2 = cable0
interfaces.ifTable.ifEntry.ifDescr.3 = cabldn
interfaces.ifTable.ifEntry.ifDescr.4 = cablup

interfaces.ifTable.ifEntry.ifType.1 = ethernetCsmacd(6)
interfaces.ifTable.ifEntry.ifType.2 = docsCableMaclayer(127)
interfaces.ifTable.ifEntry.ifType.3 = docsCableDownstream(128)
interfaces.ifTable.ifEntry.ifType.4 = docsCableUpstream(129)

interfaces.ifTable.ifEntry.ifSpeed.1 = Gauge32: 10000000
interfaces.ifTable.ifEntry.ifSpeed.2 = Gauge32: 0
interfaces.ifTable.ifEntry.ifSpeed.3 = Gauge32: 30341646
interfaces.ifTable.ifEntry.ifSpeed.4 = Gauge32: 5120000

At first glance, I was going to use the cfgmaker output for interfaces 3 and
4.  But when I looked at the speed of interface 3 versus interface 1
I decided that interface 1 really represents the downstream connection.  Is
this correct?  If so, what is interface 3?

Graphing interface 1, I see values for in/out and a calculated percentage.
This percentage exceeds 100%.  Does this make sense?  Why?  If it's only a
downstream channel, why is there an in value at all?

Graphinsg interface 4 (the upstream interface) I am only getting out values
but not in.  I guess that's because the upstream interface only sends traffic
one way.  Is there a way to combine in/out so I can see how the two mesh?

How do these graphs translate into showing me overall bandwidth usage?  In
other words, how does this allow me to understand whether my cable connection
is fast enough for the amount of traffic I am putting through?

My ISP tells me that I gaet 10mbs downstream and 1mbs upstream.  Other than
for interface 1, I am not seeing those values.  Does that make sense?


Jake Colman                     

Principia Partners LLC                  Phone: (201) 209-2467
Harborside Financial Center               Fax: (201) 946-0320
902 Plaza Two                          E-mail: colman at ppllc.com
Jersey City, NJ 07311                  www.principiapartners.com

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