IPv6 DHCP Configuration – Step-by-Step Guide

I don't know the answer to your question, but I just want to warn you about using the DHCP server address as your default router. If that works it is by chance... In IPv6 the default route is communicated by RA's and not by DHCP.

You will need to enable forwarding, accepting RA's and sending out RS's. A problem here is that the kernel included in Centos6 does not allow you to do that. When forwarding is enabled then accepting RA's and sending RS's is disabled. There should be a CentosPlus kernel with the relevant patches though. See the mailing list thread / message at http://lists.centos.org/pipermail/centos/2011-April/thread.html#109756

The relevant sysctl.conf settings are:

net.ipv6.conf.all.forwarding=1
net.ipv6.conf.eth0.accept_ra=2
net.ipv6.conf.eth0.accept_ra_defrtr=1
net.ipv6.conf.eth0.router_solicitations=1

I cannot test with Server 2008, but the following should work:

To add a tunnel from command line, run netsh and type:

interface ipv6

add v6v4tunnel Tunnelbroker localaddr=<local_v4_address> remoteaddr=<tunnel_v4_endpoint>

add address Tunnelbroker address=<client_v6_endpoint>
add address Tunnelbroker address=<routed_prefix>:1 

add route ::/0               interface=Tunnelbroker            publish=yes
add route <routed_prefix>/64 interface="Local Area Connection" publish=yes

set interface Tunnelbroker            forwarding=enabled
set interface "Local Area Connection" forwarding=enabled advertise=enabled

Replace <local_address> with the server's IPv4 address (the external one in your case with PPPoE, internal if the server itself is behind a NAT).

Replace <tunnel_endpoint> with the IPv4 address of your tunnel's server endpoint (given in the Tunnelbroker tunnel info page).

Replace <prefix> with your tunnel's IPv6 "Routed /64" prefix, for example, 2001:470:1f0b:614:: (given in the tunnel info page).

This only configures IPv6 Stateless Autoconfiguration. After the tunnel is created (the first 3 commands might be enough), you should be able to create DHCPv6 scopes in the DHCP management console. Someone who can test it on Server 2008 should expand this part...