When setting up the DNS Forwarding service, I was not allowed to put an IPv6 address for the name-server.
I had to work around the problem by dropping back to an IPv4 address for the name-server:
dns {
forwarding {
cache-size 1000
domain localdomain {
server 127.0.0.1
}
listen-on lo
listen-on eth1.5
listen-on eth1.2
listen-on eth0
name-server 8.8.8.8
name-server 8.8.4.4
}}