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Re: Cable Modem [really responsible engineering]

  • From: Fletcher E Kittredge
  • Date: Fri Jun 29 14:11:28 2001

On Thu, 28 Jun 2001 17:57:14 -0400 (EDT)  Greg A. Woods wrote:
> In the second case you'll note that docsDevCpeTable normally contains a
> list of all the IP#s the cable modem sees on the CPE interface(s).
> Besides the customer "error" scenario our modems get 169.254/16
> addresses stuck in them whenever some junior admin does something stupid
> (eg. to the DHCP server).  It's really not that hard to find them all
> and clear them all out (and of course once you've done it once you'll
> have already written a script to automate it, right?).

This works when the modem is on, and when you don't have a large
number of modems...  For a large number of modems, running that number
of smtpgets when there is an active problem to be solved is not fun.

How would you do historical data?  How frequently would you poll the
CPE to put together your history?

> You do have your modems locked down enough that CPE devices can't send
> to or spoof as a source the private addresses you use for the modems
> themselves, don't you?

Teach your aged grandmother to suck eggs, Greg.

> > Exactly. I found doing such scans got old years ago.  Not to mention,
> > it doesn't scale well :) Let n be number of customers, then finding a
> > particular MAC is order O(n) where "O is something unsavory" because
> > of individual queries of cable modems which may or may not time
> > out...  People turn the damn things off! 
> 
> Remember what I said about caching and updating the cache?  That's how
> you handle the scaling issue (and improve the realtime accessibility of
> the information too).  This really isn't a difficult problem to solve.
> You should quit running around like a chicken with your head cut off and
> instead just sit down and look at what's already sitting in front of you.

Ouch, the chicken thing really hurts... Did you know I was a chicken
farmer? 

Greg, with all due respect, I have been doing all of this for longer
than you :) Back around 1986, I realized that there are no original
ideas in an Internetworked world.  Given the same problem, people tend
to come up with the same solutions.  Especially since nanog readers
tend to share the same paradigms...

Anyhow, we tried these ideas in the early days.  This conversation
arises out of the problems we had.

I am done with this thread; thank you.

sincere regards,
fletcher




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