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I noticed that some of my Centos boxes have IP6 enabled, and seem to have addresses. I have no problem with this, but I would like to get a handle on it, and even connect to them using IP6. This would really help if for any reason DHCP has a hiccup.

But I'm a bit lost as to where the configuration on my CentOS box is. (I am also on google researching this, but I like server fault! :) )

I am hoping that I would be able to log into this via the VPN because every now and then that DHCP device has a bad morning, and needs to be restarted. (I'm also looking into this issue, but someone else handles that, management separation gone mad!) It's a remote client, so it would be a lot easier for me to connect to these systems which seem to self configure, to use that as a pivot via ssh tunnels to get to other remote devices to continue to manage them, while out main route is fixed.

I guess, my questions are

  • How can I configure IP6 without interfering with IP4, and
  • On CentOS, can I influence this auto configuration I seem to be seeing?
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2 Answers 2

up vote 3 down vote accepted

If you are seeing the fe80 address, this is the link local address. It's used for network discovery and other administrative functions, not to run services on. Every IPv6 interface has one.

The "correct" way to this, assuming you don't have a ipv6 connection from your provider, is to get a ipv6-in-ipv4 from http://tunnelbroker.net and have a computer setup on your network as a ipv6 gateway/firewall. It's easy to do, however, this will give every ipv6 ready device on your network a direct public available IP address. If you don't get your firewall right, bad things will happen.

Anyway, it's a 4 step processes.

  1. Tunnelbroker.net will provide you with the commands you need to run to bring up the ipv4 to ipv6 interface on your gateway.

  2. You configure your firewall to forward traffic. In my case, I have it also blocking any incoming connections to any port on any other computer.(no NAT in IPV6)

  3. Setup radvd on the gateway to broadcast that it's the IPv6 gateway to the network.

  4. All the other IPv6 compatible devices on the network will auto configure their IPv6 interface and now have a public IPv6 IP address in addition to the fe80 address. Test and Enjoy.

I run a dual stack network like this at home and I can provide the shell scripts I have written if you want to go this route.

It sounds like you are not the uber-admin at your network, and since doing something like screwing up the firewall settings can expose every host on your network to the Internet, I would make sure you have permission first.

Oh, and this will not affect IPv4 in anyway.

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i love this answer. I really, really do. Oh boy! My home network will not know WTF hit it! Are you kidding me!? For the next 10 days, I am unavailable via IP4! :) Oh yes, and I will fix my clients network too! hehe! –  Mister IT Guru Mar 22 '11 at 11:24
    
They are indeed link local addresses, by the way. –  Mister IT Guru Mar 22 '11 at 11:25
    
I thought I had already accepted this answer! Apparently not! Thank you for the links and the heads up. If all goes to play I should be one click away from all the servers I manage! Thanks again. –  Mister IT Guru Mar 30 '11 at 9:10

The most important thing is whether the infrastructure providing connectivity to your server supports and routes IPv6 traffic. If it doesn't, then you can configure IPv6 as much as you like, but you'll have to go through some extra steps to get IPv6 connectivity.

If you don't have IPv6 provided to you, I'd recommend looking at http://sixxs.net or http://tunnelbroker.net, both providers of IPv6 tunnels. These basically provide a way to get IPv6 to your server by tunnelling it over IPv4. There's quite extensive documentation on both sites on how to get this up and running.

If you're provider does support IPv6 routing, contact them about getting an IPv6 address (or /64 subnet) allocated to you.

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