[mrtg] Re: CableModem Interfaces

[Christopher A. Congdon]

I don't know the ins and outs of cable modems in general, but it seems
to me that what you *should* see if this thing adheres to certain
standards...

Interface 1) You should see inbound and outbound traffic. Inbound should
represent the traffic you are sending from your network to the 'net.
Outbound should represent traffic your modem is receiving from the 'net
and being transmitted to your network.

Interface 2) This is probably some sort of 'internal' interface. Many
devices have if's like this and can be ignored.

Interface 3/4) You may want to look into combining these two interfaces
as the same graph. I'm not sure why they are separately listed
interfaces, but IF3 should be your Internet to LAN traffic and IF4
should be your LAN to Internet traffic.

Interface 5) This would be the traffic you would see if you had a USB
cable hooked up to your cable modem. If you're not using USB, you can
comment out this IF.

If your server is doing most of the Internet traffic on your network, it
is no surprise that the IF3 matches your server's inbound traffic. Since
your server is pulling packets from the 'Net, they have to follow
through the inbound interface on your Cable Modem, which is IF3. You
should see a matching graph of Outbound Traffic color on the Cable's
IF1. This also means that your server's ETH0 outbound should be a close
match for the cable's IF4.

Judging by the Configmaker interfaces, it is no surprise that IF4 only
shows outbound traffic. IF1 however should show inbound and
outbound...after all, it should be a standard Ethernet interface.

Again, your best bet is to have MRTG make two graphs for you, one
showing inbound and outbound for the cable's IF1, and a combo graph
showing IF3 as inbound and IF4 as outbound traffic.

Chris

> -----Original Message-----
> From: mrtg-bounce at list.ee.ethz.ch [mailto:mrtg-bounce at list.ee.ethz.ch]
On
> Behalf Of Jake Colman
> Sent: Tuesday, June 07, 2005 09:00
> To: mrtg at list.ee.ethz.ch
> Subject: [mrtg] CableModem Interfaces
> 
> 
> I have a cablemodem connected to eth0; eth1 is used for the internal
> network.  I used cfgmaker to create a config for eth0 and for the
> interfaces
> on the cablemodem (a docsis-compatible SB5100).
> 
> I don't understand what the various cablemodem interfaces mean nor do
I
> understand how I can use these interfaces to graph the bandwidth I am
> using
> when connected to the internet.
> 
> cfgmaker found 4 interfaces on the SB5100:
> 
> 1) ifType: ethernetCsmacd (6); ifName: eth0
> 2) skipped
> 3) ifType: CATV Downstream Interface (128); ifname: <none>
> 4) ifType: CATV Upstream Interface (129); ifname: <none>
> 5) ifType: (160); ifName: usb0
> 
> The downstream interface (interface 3) seems to have exactly the same
> graph
> for incoming bytes as that shown for my server's eth0 interface.
> 
> Interfaces 1 and 4 show only outbound bytes but I have no idea what
this
> represents.  Can anyone explain?
> 
> Ultimately, what I'd like to graph is the amount of my available
bandwidth
> that I am currently consuming in both directions.  Any suggestions how
to
> do
> this?
> 
> TIA!
> 
> ...Jake
> 
> --
> Jake Colman
> Sr. Applications Developer
> Principia Partners LLC
> Harborside Financial Center
> 1001 Plaza Two
> Jersey City, NJ 07311
> (201) 209-2467
> www.principiapartners.com
> 
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