Hmm. I doubt Comcast is actually doing this - they are far too busy actually
trying to build a network, out of the ashes of the @home debacle. However,
even if they were, there isn't really anything wrong with it. We scratch our
heads, collectively, when a large broadband provider goes chapter 11, but
then oppose a pricing model that might be profitable. Now, if a provider was
refusing to provide extra IPs, then I could see the problem. However, if a
provider is willing to provide extra IPs for something reasonable like
$5/month, more power to them. There are several good reasons why they might
want to ban NAT:
1 - When you come to the stadium, you can't bring in your own hot-dogs. It's
the same sort of thing - the hot dogs are subsidizing the ticket price. In
this case, extra fees for things like IP addresses and extra email boxes,
are the concession items.
2 - Support issues - supporting a largely clue-challenged user base, is hard
enough without people slapping linksys routers in, then expecting the ISP
to, defacto, provide support. Anyone remember when the only supported router
for UUNet ISDN lines was the Pipeline 50? This was to (in theory) enable
supportability
Especially considering the clue-challened support departments at Cable ISPs, this is a legitimate problem.
Newer Linksys and similar routers can spoof the MAC address of the PC that's behind them as a way to avoid having to tell the cable company about the new "computer." Connected backwards, the Linksys routers appear to merrily spoof the default gateway off the segment (i.e. most likely the first MAC address the box hears) and create lots of support headaches.
3 - NAT is wonderful, but we aren't running out of IP addresses that
quickly, and NAT will break some applications. Large scale NAT is probably
not the solution to future IP address exhaustion problems. Providers who do
this are not being bad guys, because extra IP addresses cost less than the
costs of supporting NAT boxes. If folks don't like this, they can become
involved with ARIN and propose some bizarre price-support scheme for IP
addresses, to encourage NAT, I suppose.
Well, NAT saves the cable company from having to route subnets. ATT Broadband in Massachusetts is now offering "business" service. Reading the fine print, they provide a NAT router, and say you can have up to 253 users behind it. Of course any apps that wouldn't work with NAT will not work.
As such, clearly they DO support and/or allow such use of routers. Actually, they've been doing this for a long time. They supply cable service to many schools in the area, and those are all supported using NAT boxes.
4 - This is, of course, an unenforceable policy (which is why I suspect it
does not exist). However, it is very reasonable for a provider to refuse to
support a customer with a NAT box, if the customer is buying a single user
service.
Support is one thing. Trying to detect the presence is another entirely. Wasting time, effort and money trying to track down users who're using "cable routers" is looney.
