While Comcast is a large provider, what they do is different from what someone like the large backbone providers which have peering arrangements. Because Comcast (like all Broadband providers) has a MUCH larger amount of endpoints than your typical WAN/Backbone provider it is always going to have more data being pushed to it than it sends. That will never change and it is their business model but they now want to be treated like they are a transit provider when really they are just a data sink. Comcast wants to say its just because of the vast discrepancy of traffic but content delivery is always going to use a lot of bandwidth and to get around "net neutrality" by just claiming its not the content but the amount of traffic is just a lousy excuse to disguise the true reason.

Yes, there will be Carrier Grade NAT (CGN) used for the time to be. You will primarily see if in Mobile Wireless networks for handsets that don't require a full Internet connection but other ISP's will eventually be forced to do the same. That said, CGN is required so that we can do Dual Stack (where you have both an IPv4 and IPv6 address). This is the most commonly accepted transition technique and really the best available. It works by using the DNS system to determine if the name you are trying to resolve has a AAA or AAAA (referred to as a Quad A) record. The IP stacks of today are set to prefer Quad A over AAA records so if a site has a IPv6 address (or Quad A record) you will hit the site using your IPv6 connection. CGN is a IPv4 technology and not a IPv4 to IPv6 Gateway. CGN just allows us to do a massive amount of NAT44 that most of our current NAT devices can't handle.

Really there is nothing to see here that hasn't been said over and over again on every "World ending IPv4 shortage" article on Slashdot. Yes, the threat is real. Does it really matter to many people outside of Service Providers, not really because almost everyone else is doing NAT44 today anyone in one form or another. As usual, what should be taken from this is that if you are a Network Engineer responsible for managing a network, you should be taking the time to take inventory of your IPv4 space and making plans for implementing Dual stack in the near future.

I don't know enough about your environment but hopefully you know that that isn't a possibility across Layer 3 devices (and when I say VLAN's, I assume that you are talking about an IP segment and not just a VLAN number). That said the "ip dhcp helper" or DHCP relay I think is what you are looking for. This way you can have 1 DHCP server serving numerous VLAN's or L3 IP segments. If you have more specific questions feel free to reach out to me.

Carl Fugate
carl@iprouteradmin.com
BLOG: www.iprouteradmin.com
Router Lab: www.onlinerouterlab.com