There’s this great debate in the IPv6 world about how to chop up your allocation into assignments for your customers. Typically, most ISPs are being handed a /32, and general guidelines say to allow for a /48 per DSL/leased line/cable customer.

However a lot of people are asking, why not a /64?  Quoted below is the sort of answer you’re likely to receive on NANOG, by one Mark Smith:

There are a variety of scenarios where customers, including residential, will benefit from having multiple subnets. They may wish to separate the wired and wireless segments, to prevent multicast IPTV from degrading wireless performance. They may wish to segregate the children/family PC from the adult PC network or SOHO network, allowing the subnet boundary to be an additional Internet access policy enforcement point. They’ll need separate subnets if they wish to use a different link layer technology, such as LoWPAN. They may wish to setup a separate subnet to act as a DMZ for Internet facing devices, such as a local web server for sharing photos with relatives. Game consoles may be put in a separate subnet to ensure file transfers don’t interfere with game traffic latency, using the subnet ID as a QoS classifier.

This answer is quite simply unrealistic. It’s the answer of a typical geek with no sense of perspective as to what the average consumer wants. It’s the opinion of what Mark Smith the network engineer and geek would want.

In the real world, most consumers of domestic internet services have absolutely no concept of IP addresses let alone subnetting, VLANs, segregation or quality of service. Most domestic networks are a single flat subnet with NAT to a single IP address and no servers that would require port forwarding, and rarely an IPTV system, but those are usually setup to use special triple-play routers configured by the ISP. Most domestic users just want to be able to plug stuff in and have it work.

Now, people will argue that there are more IPv6 addresses than there are atoms in the world. However that argument isn’t as good when you are assigning 1,208,925,819,614,629,500,000,000 IP addresses for just 2 or 3 devices. It’s a grossly inefficient waste no matter what you say. Not to mention that if you’re one of the big cable or DSL providers with millions of customers, it makes much more sense. Each barely used /48 that you throw out contains 256 /64′s.

As such, I personally am inclined to go for the default of a /64 per customer, but allow for a /48 should they need it. There is absolutely no point in issuing a /48 subnet to someone who is never ever going to use it… it’s just laziness, which is what got us into the current situation with IPv4 in the first place.

More numbers than you can shake a stick at. Just to give you an idea, at the ISP level (/32) that’s 79 septillion IP addresses assigned. That number is so big I had to go look it up on Wikipedia to find out what it’s called. Every home user will have 18 quntillion addresses at his disposal – I don’t have 18 quntillion pieces of lint  in my house, let alone a desire to connect every single one to the internet!

A common problem with ADSL in the UK is that most connections are still using PPPoA. This means that if you want a computer to have a public IP address on one of these connections, you need to either have a block of IP addresses routed by your ISP to your router (at extra) cost, or you use a USB modem. There’s no real option for those folks that want to connect something like a SonicWall or any other firewall device directly to the line.

However, there is a poorly documented hidden “half-bridge” mode in the ZyXEL 660R routers. These cheap little single-port routers have the ability to push the public IP address and all it’s traffic onto a single device connected to the LAN port.

To do this, set the router up as normal with the username and password for your connection, then logout from the web interface. You’ll now need to telnet to the device, and enter the following:

poe bridge switch on
ip dhcp enif0 server lease 120
sys save

After this, reboot the router. Once it boots up and logs into your ISP, you should find that it gives you a single IP address on DHCP and that address will be an external fully public IP address.

Update: IntoTheUnknown uses this to build a SIP VoIP system, which of course can have problems when passing through any firewall or NAT conversion.