Cable Modem [really responsible engineering]

Thu Jun 28 17:41:55 UTC 2001

On Tue, 26 Jun 2001 16:08:13 -0400  Fletcher E Kittredge wrote:
> > >         Also, if the cable/dsl/wireless modem is a router, life
> > > becomes much simpler as one can just gather the necessary information
> > > via tracing.  However, I am not sure requiring modems to be routers is
> > > a good thing...
> > 
> > I think you should sit down and read the DOCSIS specifications
> > carefully before you say things like this.  If implemented correctly,
> > it actually works, believe it or not.   The modem does _not_ have to
> > be a router in order for it to work.
> 
> Ted;
> 
> 	Thank you so much!!  I will set right out to do so!

Ted;

	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.

	This is embarassing, but I have been spending time on the
DOCSIS 1.0 spec (http://www.cablemodem.com/specifications.html), and I
can't seem to find where this behavior is specified as required.
Could you give me some hints as to which document it is in and which
section?

        Given the DOCSIS specifications, the two mechanisms I can
think of for yielding this information are SNMP and DHCP.  In regards
to DHCP, time spend with the DOCSIS spec, your excellent book and
tcpdump says to me that it is not in the DCHPREQUEST packet, either as
'giaddr' or as any DHCP option I can find.

       Time with the RFCs and the DOCSIS spec have not yielded to me
any SNMP object in any of the DOCSIS required SNMP MIB RFCs which
would return all the the bridged MAC

	What am I missing?  Your guidance is much appreciated.

thanks,
fletcher