IPv6 Course part 2: Stable IPv6 addresses on the local network

For IPv6, Network Address Translation (NAT) not provided. Rather, it is among other Purpose IPv6, NAT to make it unnecessary. The corollary, principle that every computer has a publicly accessible IPv6 (However, the protected by the firewall or in the FritzBox. is blocked). It also means, that by default, change the local IPv6 is, if the public IPv6 change.
Also: If you have no fixed IPv6 subnet (and perhaps reasons of anonymity and will not have), then change the default, IPv6 addresses of all computers in local network accessible, if the router gets a new IPv6 subnet. Get the router using 6to4 tunnels are IPv6 subnet, then changes the IP every time IPv6, if the router gets a new IPv4.
In the local network but it can be useful, always use the same subnet. A local server can be configured in a manner, to only accept connections from that subnet. When the Web server is the apache for example with the following commands (“Ababa:Ababa:Ababa” replace the self-chosen prefix, see following paragraph):
deny from all
allow from fd00:abab:abab:abab:/64 192.168.178.0/24


To have a fixed IPv6 prefix locally, the Fritzbox offers the possibility, In addition to the public IPv6 connected computers with an IPv6 subnet to provide, This is the same, and not on the Internet is routed. It must on the Web interface of the Fritz box under “/Internet/credentials/IPv6” in the section “Unique local addresses” the option “Unique local addresses (ULA) always assign” Select, always a FD00 then get all ipv6 calculator:z:MAC address.
This subnet is then used as IPv6 replacement for the private under IPv4 IPv4s 192.168.x.y. The subnet starts with “FD00”, all such addresses for private networks are, the route not on the Internet, reserved. Should any digits in the following places (0-9 and A-F) Enter – other at each Fritzbox. You should enter other at each Fritzbox, following reason: If you are in the foreign guest, then you can connect via VPN with the local network, without that there are problems, because the local IPs in the guest- and home network are not the same.

If this option is enabled and the Fritzbox has received a public IPv6 subnet, then she shares with both prefixes to connected systems. Thus, you get two IPv6 addresses:
FD00 addresses, that have been set up just, and
2001-Address of the 6to4 tunnel.

Now we have 2 Problems:

1. When two local computers want to speak to each other, can they provide 2100- or do FD00 addresses with each other. Which they use it, is not defined. But we want to, that they use internally always the internal FD00 addresses, because otherwise a local server would, It offers its services only to FD00 addresses, not responding.
2. From the perspective of the computer you are 2100- and FD00 addresses: You do not know, that the FD00 addresses on the Internet are not routed. That is why the machines they use equivalent and you cannot be certain, always the 2100 address used for Internet traffic. With the FD00 address the routing in the Internet does not work but.

To solve these problems is a mechanism for IPv6 (Address selection, under windows “prefix policy” called) provided for, as to the use of specific source- and destination IPs can affect. In this case an entry must be added to the address selection table. Unfortunately you can add an entry in Windows XP and not simply; a new entry deletes all existing. Therefore, you must reset all entries and then add the new (in Windows 7 can you simply add, without having to reset the existing):
# In Windows XP
# Windows-Taste + R drücken, "cmd" tippen und die Enter-Taste drücken.
# In Windows 7
# Windows-Taste drückem, "cmd" tippen und mit der rechten
# Maustaste auf "cmd" Klicken und "Als Administrator ausführen"
# anklicken.

# Und das Konfigurationsprogramm verlassen
exit

In Ubuntu and Redhat this rule is set by default (see /etc/gai.conf in Linux), so on these platforms above adjustment manually need made to be (Attention: This may be different on other Linux distributions).

A precise statement of this table in Part 3 the IPv6 course.