[mrtg] Re: CableModem Interfaces

Jake Colman colman at ppllc.com
Wed Jun 8 16:32:15 MEST 2005 

Chris,

Thanks for the detailed explanation.  The way you explained it does seem to
match up with the graphs I am seeing.

Some questions/observations:

1) IF3 and IF4 just seem to be splitting up the data that I can also see on
   IF1.  Is that correct or am I missing some subtelty as to whay it is split
   that way?

2) IF1 is the same data, just in reverse, of what I am seeing on the server's
   eth0.  Again, is that correct or am I missing something?

3) If the above are correct, if I want to graph my internet traffic, all I
   really need to grapg is my server's eth0.  I don't see any value-added to
   graphing the interfaces on the cablemode.  Is this correct too?

Thanks!

...Jake

>>>>> "CAC" == Christopher A Congdon <ccongdon at congdonweb.com> writes:

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

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

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

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

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

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

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

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

   CAC> Chris

   >> -----Original Message-----
   >> From: mrtg-bounce at list.ee.ethz.ch [mailto:mrtg-bounce at list.ee.ethz.ch]
   CAC> 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
   CAC> 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
   CAC> this
   >> represents.  Can anyone explain?
   >> 
   >> Ultimately, what I'd like to graph is the amount of my available
   CAC> bandwidth
   >> that I am currently consuming in both directions.  Any suggestions how
   CAC> 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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-- 
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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