MavEtJu's Distorted View of the World

IPv6 training and thoughts

Posted on 2008-05-03 09:00:00
Tags: IPv6, Networking

After two days of the IPv6 training workshop organized by APNIC, I think I'm ready for it. Mentally that is. I will guide BarNet safely into the 21st century! (Yes, I know that that century is already eight years old, but then IPv6 is already more than eight years old)

There are a couple of interesting things about IPv6: The first one is the absence of the checksum field in the IP header. Had an IPv4 header a checksum which had to be recalculated on every router it went through (that's no fun for highspeed routers I tell you), IPv6 packets don't have to do this anymore.

The second thing is the absence of the ARP protocol: It's gone now. It's over for it. Bye! It's now part of the ICMPv6 protocol: If you need to know the ethernet address of a host, you send an ICMP packet asking for it. I'm pretty sure that RARP (RFC903) is obsolete now.

The third one is the absence of subnet broadcast address: No more all 1's, it just doesn't exist. If you want to tell something to all hosts, use a local multicast.

Related to the third one is that the network troubleshooting trick to see how many hosts are alive by pinging everybody in the subnet, which is now an /64, is obsolete, because it will take seventeen days before you have complete the full sweep.

The famous IPv6 autoconfiguration... It is great for a simple network where hosts have everything (DNS, WINS, proxy etc) statically configurated, but I don't really believe in it for a properly managed network: DHCPv6 is the way to go. Still. I will have to figure out how it works: I saw that the ISC-DHCP port in the FreeBSD ports tree was very outdated and that there wasn't a 3.1 not 4.x version in it... I will have to take things in my own hands!

With regarding to our network equipment I'm not too worried: The routing Extreme Networks boxes and the Juniper boxes do support IPv6, the Cisco PoE switches should be fine. The FreeBSD, Linux and Windows 2K3 devices do support it. And PIPE networks does support it.

With the FreeBSD boxes there is a small problem right now though... In the past we carefully designed our network and services with jails and such, and jails support only one IP address. That's the whole idea behind a jail, nothing you can do about it. And that works great, oh, except for the fact that in dual stack mode you need two IP addresses: an IPv4 and IPv6 one. I know that there are patches around for FreeBSD 7.0 to support multiple IP addresses, but that doesn't help me yet because we have just migrated everything to 6.3...

So, how can provide IPv6 access to our services easily? The simplest way is to make some kind of IPv6-to-IPv4 gateway, which translates an IPv6 packet into an IPv4 packet and forwards that to our servers.
Confused? Here is an example: has an DNS A record of The IPv6 DNS AAAA record would be 2001:0DF0:0009::CA53:B0F8 (or 2001:DF0:0009::0202:0083:0176:0248 to prevent nasty dec-to-hex conversion errors). As you can see, the last 32 bits is the IPv4 address, the first 48 bits is our network. The IPv6-to-IPv4 gateway would carefully craft an IPv4 packet with the right IPv4 address and send it of to my webserver. The answer would be translated back into an IPv6 address.

Nothing difficult, this is just plain NAT. And it would expose all our services in one go to the IPv6 world, without anything to change on the services. Okay, you would lose the information of who it really was who asked it, but that is just a small price to pay until the full IPv6 service is in place. Let's do some hacking!

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