Hey everyone. I just spent an hour or so figuring this all out so I figured I'd put all the pieces of information together in one place.
Our house had FTTH installed by the Telekom and until yesterday, we had a contract with them. Now that our initial two years are up, we switched to Vodafone to get the new-customer rate.
Vodafone unfortunately doesn't provide a dedicated IPv4 address, so IPv4 connectivity requires the use of DS-Lite. Setting up the initial tunnel connection is easy, this part came mostly from the wiki:
/etc/config/network:
config interface 'wan'
option device 'eth0.7'
option proto 'pppoe'
option username 'vodafone-ftth.komplett/***'
option password '***'
option ipv6 '1'
config interface 'wan6'
option proto 'dhcpv6'
option reqaddress 'try'
option reqprefix 'auto'
option device 'pppoe-wan'
config interface 'wan4'
option proto 'dslite'
option peeraddr '::'
option encaplimit 'ignore'
At this point however, I ended up with "Destination Port Unreachable" when I attempted to do an IPv4 ping against any destination from my LAN clients. I dug through the forums and finally found a slightly related post that had a firewall configuration attached but stated that it wasn't working. I figured "you've got nothing to lose" and indeed, I only gained: IPv4 works!
Here's the relevant /etc/config/firewall section:
config zone
option name 'wan'
option input 'REJECT'
option output 'ACCEPT'
option forward 'REJECT'
option masq '1'
option mtu_fix '1'
list network 'wan'
list network 'wan4'
list network 'wan6'
Turns out that I needed to add all of the WAN interfaces to the WAN firewall zone, not just wan and also not just wan6 xor wan4.
Everything works now and I'm good for the next two years!
Also, side note: when I signed up for the contract, Vodafone asked for the Home-ID (can be found on the FTTH box). I gave them the ID, but they mangled it and stated it as A000011 (which was not even close). If this happens to you, fear not: the day your contract starts, you have to go through a setup wizard on the Telekom website that asks for your fiber modem's serial number as well as the Home-ID once again. Supplying the correct one there is enough to make it all work.
Another side note: the Telekom internet kept working until I started the setup wizard on the Telekom website (which then cuts your connection and activates the Vodafone contract). So you don't have to do this right at midnight, you can probably just do it at some point during the day.