Hi, 

I've successfully set up IPv6 (DHCP6 PD) on my ER-605 on my main VLAN(1) and have great connectivity.

I've also got a secondary network for IOT devices (VLan ID 70) and get DHCPv4 addresses as expected but still are getting a DHCPv6 address for the main network.

On main network:

francisconroy@Franciss-MacBook-Air % ifconfig en0  
en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
    options=6460<TSO4,TSO6,CHANNEL_IO,PARTIAL_CSUM,ZEROINVERT_CSUM>
    ether ac:c9:06:09:c6:d0
    inet6 [REDACTED]:7552:68::108 prefixlen 64 dynamic 
    inet6 fe80::48d:93e9:49b7:f859%en0 prefixlen 64 secured scopeid 0xc 
    inet 192.168.68.108 netmask 0xffffff00 broadcast 192.168.68.255
    inet6 [REDACTED]:7552:68::101 prefixlen 64 dynamic 
    nd6 options=201<PERFORMNUD,DAD>
    media: autoselect
    status: active

On IOT network:

francisconroy@Franciss-MacBook-Air % ifconfig en0
en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
    options=6460<TSO4,TSO6,CHANNEL_IO,PARTIAL_CSUM,ZEROINVERT_CSUM>
    ether ac:c9:06:09:c6:d0
    inet6 [REDACTED]:7552:68::108 prefixlen 64 dynamic 
    inet6 fe80::48d:93e9:49b7:f859%en0 prefixlen 64 secured scopeid 0xc 
    inet 192.168.70.102 netmask 0xffffff00 broadcast 192.168.70.255
    nd6 options=201<PERFORMNUD,DAD>
    media: autoselect
    status: active

IPv6 config in ER-605

IPv4 setup

It's possible that I've just misunderstood this and the address should remain the same? Should this setup work?

The connectivity on the other network isn't working consistently and DNS isn't working.

I'm going to turn off IPv6 on the IOT network and see if things start working for me for now.