[mrtg] Re: mrtg on a cable modem

[Bryant Loftin]

You can try directly connecting to your cable modem and do a SNMP walk on
public at 192.168.100.1 I read this is a factory default for many cable modem
LAN side interfaces (assuming your ISP hasn't tweaked it). Then look for an
OID that has an IP value like 10.2.222.3 or 172.17.3.4 most likely your
provider us using 10.0.0.1 or 172.17.0.1 as gateway's so it's not going to
be those.

My Toshiba wouldn't play this game so...

This is what I did to get my WAN side modem IP:

Environment:  I'm using W2K and have netmon with driver from SMS2.0 loaded
for promiscuous packet sniffing. 
I Directly connected to the modem; no router etc.
W2K is set for same IP network range as the modem internal interface
192.168.1.2 255.255.255.0 (most DOCSIS cable modems come from the factory
with the internal (LAN side) IP set to 192.168.100.1. I don't know if this
is a standard?

Turn off cable modem, turn on packet sniffing, turn on cable modem.

The first packet to come through was a DHCP nack from WAN side containing
the IP for my modem. I was surprised to see this show up on the LAN side but
it worked. Both LAN and WAN sides reply to SNMP reads using public. 

Side note:
My standard setup is using a linksys befsr11 between my boxes and the modem.
So when the befsr11 is in place the LAN side IP isn't routed but with port
161 enabled I can still get read's from the WAN side IP.

have fun.
bjl


-----Original Message-----
From: Williams, Garth [mailto:gkwilliams at epcor.ca]
Sent: Thursday, January 31, 2002 2:58 PM
To: Mrtg (E-mail)
Subject: [mrtg] Re: mrtg on a cable modem



	I have been working this avenue myself recently.  Using Ethereal and
the PCAP driver, I am able to get the MAC address of my cable modem.  Any
ideas on how to proceeed to get its IP address with this information?

	g

	<snip>
> You will also have to jump through hoops to get your Cable modem IP
> address.
> 
	</snip>


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