North American Network Operators Group

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Re: rfc1918 ignorant (fwd)

  • From: Jeff Wasilko
  • Date: Wed Jul 23 19:23:49 2003

On Wed, Jul 23, 2003 at 06:03:13PM -0400, Daniel Senie wrote:
> At 02:11 PM 7/23/2003, Dave Temkin wrote:
> >2003 7:07 AM:]
> >> Comcast and many others seem to
> >> blithely ignore this for convenience sake. (It's not like they need a
> >> huge amount of space to give private addresses to these links.)
> >
> >ARIN required cable operators to use RFC 1918 space for the management
> >agents of the bridge cable modems that have been rolled out to the millions
> >of residential cable modem customers.  Doing so obviously requires a 1918
> >address on the cable router, but Cisco's implementation requires that
> >address to be the primary interface address.  There is also a publicly
> >routable secondary which in fact is the gateway address to the customer, 
> >but
> >isn't the address returned in a traceroute.  Cisco has by far the lead in
> >market share of the first gen Docsis cable modem router market so any trace
> >to a cable modem customer is going to show this.
> When MediaOne (remember them?) deployed the cable modems here (LanCity 
> stuff, originally), traceroutes did NOT show the 10/8 address from the 
> router at the head end. ATT bought MediaOne, and now we've got Comcast. The 
> service quality has stayed low, and the price has jumped quite a bit, and 
> somewhere along the line a change happened and the 10/8 address of the 
> router did start showing up. Now it's possible the router in the head end 
> got changed and that was the cause. I really don't know.

That's exactly what happened. The Lancity equipment were bridges,
so you never saw them in traceroutes. The head-end bridges were
aggregated into switches which were connected to routers. 

The Cisco uBR is a router, so you see the cable interface (which
is typically rfc1918 space) showing up in traceroutes from the CPE out. 
Note that you don't see it on traceroutes towards the CPE since you see 
the 'internet facing' interface on the uBR.