Our initial test environment was configured for a 6RD prefix of 2602:240::/32, and changing the prefix lenght for production was overlooked. I have updated our configuration to use 2602:240::/28, so please give your same configuration another try and report back!
For anyone who would like to try manual tunnel configuration on a unix box, the following steps should be useful.
Example IPv4 Address: 188.8.131.52
A useful tool for converting your IPv4 address into a usable 6RD address is available at http://silmor.de/ipaddrcalc.html
under the ' IPv4 to IPv6 Transitional' section
Convertion tool information:
Provider prefix IPv6: 2602:240::/28
Customer IPv4: 184.108.40.206/32 (replace with your IPv4 address)
* Click 'ISP -> Customer' and use an IP from the resulting "IPv6 Customer prefix"
Example output: 2602:243:200E:4020::/60
ip addr add 2602:243:200E:4020::1/60 dev eth0
ip tunnel add 6rd mode sit local 220.127.116.11 ttl 64
ip tunnel 6rd dev 6rd 6rd-prefix 2602:240::/28
ip addr add 2602:243:200E:4020::1/60 dev 6rd
ip link set 6rd up
ip route add ::/0 via ::18.104.22.168 dev 6rd