IPv6 - Public IPs, private IPs, IPs derived from the MAC address? Confused!

I'm pretty much excited for IPv6 because of the large address room and (potential?) owning of more than one IP, or even tens of IPs (/122 subnet?)

Though one magazine has now confused me.

In a current issue (no. 3) of "CT", a German computer magazine, I read that when using IPv6 your IP address consists of your MAC address and various other things, and that this address will be public on the web, no matter what access point / LAN you connect to.

My knowledge of IP(v6) is in contrary of this. I thought you will normally always have a a local network IP and NAT takes care of your Internet access, and your provider gives the NAT router an IP.

I've heard of the 6to4 interface, but does this one give you your own ip in the IPv6 net?

Personally I hope it still is through a personal IP space (like 192.168, 127.16-31, 10. in IPv4) in private networks with a NAT going to the Internet. And also I hope that providers will offer subnets to private customers so they don't have to use NAT anymore. Yay for converting your LAN into the WAN and using better security (so Computers from the same subnet still get access rights like normal).

sinni800

Posted 2011-02-23T15:15:26.413

Reputation: 3 048

On the Internet, no one cares what your MAC address is. – Ignacio Vazquez-Abrams – 2011-02-23T15:20:18.060

2Still your MAC address uniquely identifies your device wherever it is! If someone outside would get ahold of it he could track you. – sinni800 – 2011-02-23T15:28:18.257

Answers

Your magazine is right. IPv6 address consists of two parts: network prefix and host address.

If host address is not assigned, then computer autogenerates it, usually by using MAC address. Which means your IP includes something that uniquely identifies you, not depending on what network you are using.

See for example Wikipedia page for more information. There is also another post in superuser.com explaining how to disable using MAC address in different operating systems.

Olli

Posted 2011-02-23T15:15:26.413

Reputation: 6 704

So the one that the computer generates is the Link Local address? It makes sense when you can clarify that. – sinni800 – 2011-02-24T08:49:17.717

@sinni800: usually network router advertises network prefix, and host generates host address. That's not link-local (as in link-local addresses in IPv4), it's visible to public internet when you connect to somewhere. – Olli – 2011-02-24T08:57:58.903

Wow, this completely answered what I was trying to get. So you now USUALLY don't just give the NIC the whole address, but rather just give it the network portion by DHCPv6 and the host itself makes the host portion? – sinni800 – 2011-02-24T10:08:16.403

@sinni800: it really depends on network configuration. I think normally IPv6 network is configured with for example radvd (Router Advertisement Daemon). That way computer gets network prefix and router address. Then computer selects host address automatically. But you can also use DHCPv6 (but not all operating systems include (native) IPv6 DHCP client). That way local router/server provides full address to client (your computer). – Olli – 2011-02-24T11:24:54.250

Yes, there are private IP addresses in IPv6. I'm shocked that no one has objected to answers that claim otherwise (and I don't have enough reputation to comment).

They are called Unique Local Addresses and as of 2018, they are basically limited to fd00::/8.

They cannot be used with NAT the way IPv4 private addresses are used, however.

Yes, NAT does actually exist in IPv6, but not in the form of the "masquerade NAT" used in IPv4 (it serves a different purpose). It is called NPTv6 and it's used for prefix translation.

LubosD

Posted 2011-02-23T15:15:26.413

Reputation: 121

There is no "private" IP addresses in IPv6. (There is LinkLocal, but that is a bit different).

NAT Will no longer exist. Most companies trialing it, such as comcast, are giving out 32 bit addresses to each consumer modem. that would give you 4 billion IP addresses to use with your connection. (right about how many IPv4 Addresses there are in the world right now)

Firewalls will still be critical, but will not have to do NAT anymore. Things like person to person video chat will really work correctly.

Brian

Posted 2011-02-23T15:15:26.413

Reputation: 2 934

Ahhh. Thanks a lot, this does not clear the MAC thing the magazine explained though. They said that you'll have a public ipv6 address which consists of your mac and some other set things when you connect to a network, not how you just said it... – sinni800 – 2011-02-23T15:29:53.573

This is quite misleading. See for example http://en.wikipedia.org/wiki/IPv6#Address_Format , "The host address is often automatically generated from the interface MAC address.". Your magazine is right on this thing.

– Olli – 2011-02-23T15:48:30.633

Hmmm. So WHEN is the host address generated from the MAC address. Only at link-local level or where? – sinni800 – 2011-02-24T08:50:09.853

Uh.. About the comcast thing. Do they give you a /32 SUBNET or 32 bit of HOST ADDRESSES? If it was 32 bit of host addresses we'd have a /96 net. – sinni800 – 2011-02-25T09:02:05.320

There are only public IP addresses in IPv6. Thus, no NATing will be required at all.

The smallest block of IPs possible will be in the thousands, not just a few. Each person will be allocated thousands of IPv6 addresses.

There will be enough IPv6 addresses for every molecule on the face of the earth to have its own address (not inside the earth as well, just the face).

Tacticious

Posted 2011-02-23T15:15:26.413

Reputation: 9