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I'm trying to get IPv6 working for a big school project. I have a Dualstack line with an IPv6 ready modem. The server and client get there IPv6 automatically, but when I want to use static ULA addresses I can't connect to the IPv6 DNS server 2001:4860:4860::8888. I just want to give an easy to remember IPv6 address so that I can work with those addresses easier inside my network.

The modem has already got an ULA address which is fd00::c225:6ff:feb5:9595/64. I gave my client an IPv6 adres which is fd00::21/64 and the gateway and dns are fd00::c225:6ff:feb5:9595 which is the modem/router. This is somehow not working.

My question is what am I doing wrong and is my idea even possible?

Thank you in advance.


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up vote 1 down vote accepted

First of all, you are not supposed to pick a ULA address block, you are supposed to generate a random one. If you don't then you run the risk of conflicting addresses when setting up VPN connections to other networks that have done the same. Fd00::/48 is an especially bad choice in this regard... Also see

Second, IPv6 has no NAT. So while you can use ULA addresses for internal communication you can't reach public addresses (such as the public Google DNS servers) from them. Your ISP will filter all traffic that doesn't have a source address from the block of addresses that they delegated to you. You need to either give the clients a global address from that block in addition to the ULA address, or you need to proxy everything. You can also use only the addresses from your ISP and no ULA.

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Thank you Sander Steffann for your reply. I found out that when I want to make a static address that I indeed need to use Global addresses instead of ULA's. The first 64 bit are the subnet and the last 64 bit can be used for my clients, or am I wrong with this? Also is there a way to give the clients an easier address next to the Global address? I know that you can give a NIC two addresses so that is why I'm so curious. – Jonathan Feb 14 '12 at 8:27
You can use all combinations of global and ULA addresses. You can give a PC both an auto-generated address, static addresses and DHCPv6 configured addresses, all at the same time. The problem will be how to manage all that in your operating system... – Sander Steffann Feb 15 '12 at 20:24

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