Depends on the location. If iWay does have a POP in your network, they can offer native IPv6 because their DHCP does support it. If they don't have a POP, they often (need to) use Swisscom to "proxy" your packages (like Crossover7). And because the Swisscom DHCP Server can't assign IPv6 leases currently, your router needs to tunnel IPv6 packages in IPv4 packages to the infrastructure of iWay.
https://de.wikipedia.org/wiki/6rd