Implications of using IPv6

Is there a guide to the implications of using IPv6 on a broadband connection?

a) Would you have to use IPv6 on your home network? or could you continue with IPv4 via NAT?

b) How would Dynanic DNS work? What happens if an external IPv4 device such as a mobile phone, or a laptop in a hotel, wants to contact a server on your home network?

a) You can run both IPv4 (NAT if required) and IPv6 in unison with no issues. I am running exactly this setup just now.

b) Dynamic DNS basically disappears. For auto configuring internal clients, there is DHCPv6 available but it's not what I use just now. I currently use RADVD (Router Advertisement Daemon) which allows for IPv6 aware devices to auto configure themselves with a specific address based on the network prefix I've configured the daemon for (based on what my ISP delegate me). Ordinarily, the last 64 bits of this address are based on the MAC address of the connecting device and so the complete 128 bit IPv6 address becomes static, meaning the requirement for dynamic DNS disappears. Windows machines have a little trick which you can enable which randomises the last 64 bits of the IPv6 address it will use when chatting to the RADVD so the address is no longer fixed and predictable (a possible security improvement). AAISP route me a static dedicated /48 prefix to my connection. I only use a single /64 of this however, as that is what RADVD expects to be configuring IPv6 clients on.

If you're talking about translating an external IPv4 address to an internal IPv6 address (similar to NAT, but IPv4->IPv6), then I'm not too up to speed on that yet - but further reading is available here: http://en.wikipedia.org/wiki/IPv6_transition_mechanisms - the only way I know of doing that just now is by using a dedicated proxy program (like 6tunnel) which listens on IPv4 of the host server/router, and forwards connections onto an IPv6 host.

If you are in a public location such as a hotel etc, best to just use a tunnelled IPv6 over IPv4 connection like what http://tunnelbroker.net/ (Hurricane Electric) provide. Once that's setup, you'll be able to reach internal clients on your home network. If your ISP doesn't yet support native IPv6, setup one of their tunnels for your home network as well. Once both ends are connected to IPv6 via tunnels, direct connections are then possible (and will appear to be completely native / transparent).

Thanks for your reply I can see the subject its quite complex.

But in point 2 are you not confusing Dynanic DNS with DHCP?

With Dynamic DNS I can always find my router from say a hotel, because even though it uses an address randomly assigned by my ISP I can find it because it registers itself so that my domain name always points to it.

It could be that with IPv6 there are so many addresses available that my ISP would always assign me a fixed address.

In reply to a post by Michael_Chare:

But in point 2 are you not confusing Dynanic DNS with DHCP?

I wasn't sure if you were referring to the IPv6 address of the router, or hosts with IPv6 addresses on your LAN. In any case, my points still stand. The ISP will delegate and route to your connection a fixed IPv6 prefix (a /64, or in my case, a /48 which allows multiple /64's). The router is then configured with any static IPv6 address that lies within that prefix, but for simplicity and to avoid conflict with other hosts on the LAN, I tend to use the very first address of the delegated prefix. So for example, if my prefix is 2001:A:B:C::/64, I'll set the router to have IPv6 address 2001:A:B:C:: (which is 2001:A:B:C:0:0:0:0).

Hosts on the LAN will then have IPv6 addresses 2001:A:B:C:X:X:X:X where, if using RADVD, the last 64 bits (the X:X:X:X) become predictable as they are based on the MAC address of the client (using EUI-64). See http://waldner.netsons.org/f3-eui64.php - if I have a prefix of 2001:A:B:C::/64 and my MAC address is 00:01:02:03:04:05, my IPv6 address will always be 2001:A:B:C:201:2FF:FE03:405 (static) if RADVD is auto-configuring my client.

As you can see, you don't really have to worry about changing IP addresses any more, and so don't have to worry about dynamic DNS - you'll always know what clients have what addresses, since there is a direct mapping between MAC address and final IPv6 address. All you have to do is set these addresses up on any domains you have as static AAAA records (make sure your DNS servers support AAAA records, of course, which is the IPv6 version of A records).

I mentioned DHCP (and probably confused you) as there is currently another way of auto-configuring clients with IPv6 addresses - DHCPv6. I've not used this at all, but depending on how that is configured, I would imagine it is very similar to standard DHCP. So, you can either make IPv6 clients on your LAN have the same IPv6 address each time they connect (like RADVD) or, give them a different address each time. If the latter, this then does cause a requirement for Dynamic DNS as such clients will have constantly altering IPv6 addresses. But in this case, why configure the client to have a changing IPv6 address at all? If you are wanting to connect to it in the first place, best to make it static and leave it that way so you'll always know what the address is.

On a final note, the difference between DHCPv6 and RADVD is subtle but important. [RADVD doesn't know about DNS servers, or anything else]*. DHCPv6 does. Because I run standard (IPv4) DHCP on my LAN, all my devices get their DNS and domain settings from this, and the RADVD part is like a 'bolt-on' to configure their IPv6 address. If I was to go completely IPv6 (and remove IPv4), I'd have a problem because I would have the auto-address configuration part of IPv6, but not the rest of the package (eg. clients wouldn't be told what DNS servers to use to resolve stuff etc). This is why I'm sure DHCPv6 will eventually become mainstream, and RADVD rendered redundant in due course.

* - just noticed this isn't entirely true anymore: http://tools.ietf.org/html/rfc6106 - things are moving too fast these days!

Edited by deleted (Sun 15-Jan-12 05:33:03)

Thanks very much for your reply. I am beginning to understand a bit more now.