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Re: Cable Modem [really responsible engineering]

  • From: Greg A. Woods
  • Date: Thu Jun 28 15:53:15 2001

[ On Thursday, June 28, 2001 at 13:41:55 (-0400), Fletcher E Kittredge wrote: ]
> Subject: Re: Cable Modem [really responsible engineering] 
>
> 	I haven't been able to figure your statement above out.  I
> thought you were saying that given a client device MAC address, one
> could determine which cable modem MAC address was servicing that
> client MAC, even in the cases where the cable modem was just acting as
> a bridge.

Luckily not much of this thread has been polluting NANOG, so I'm not
100% sure what your goal is here, but I will point out that:

The client-IP addresses active on any CPE interface of any cable modem
compliant with the DOCS-CABLE-DEVICE-MIB (rfc2669) can easily be
discovered with SNMP.  From there it's very simple to find the client
MAC in your dhcpd.leases file (though I don't know why the IP#s wouldn't
be sufficient for most needs).  Note too that this same table should
also act as a filter to lock static addresses to a given modem if its
entries are assigned by the operator.

The only problem of course is that you've got to SNMP-scan all your
modems to find which customer's using a given IP# (I did that a couple
of times just this morning! ;-).  There are no doubt ways to cache this
information, and maybe even refresh a cache intelligently.  There may
even be a better, proprietary, way do do such searches in well
implemented head-end systems (doesn't seem to be in Terayon's though).

-- 
							Greg A. Woods

+1 416 218-0098      VE3TCP      <gwoods@acm.org>     <woods@robohack.ca>
Planix, Inc. <woods@planix.com>;   Secrets of the Weird <woods@weird.com>




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