Community Fibre with Unifi and a gotcha

— 3 minute read

A Gotcha permalink

I just moved over to Community Fibre and discovered a gotcha that will cost me about £200 over the next two years.

If you want a public IP, or if you want an IP that's not behind carrier grade NAT (CGNAT), and you're with Community Fibre make sure you get a 500 Mbps package or above. I went for 200 Mbps, waited for three weeks until my Virgin contract ended, discovered this and was told I couldn't get introductory offers after the 14 day grace period. That's an eight pound difference every month for two years that they wouldn't negotiate on at all.

Why would you want a private IP? So that you can forward ports to devices internally. If you're behind the CGNAT you can forward ports on your router's NAT all you like and it won't work because the CGNAT isn't forwarding them to you.

IPv6 permalink

If you want to use IPv6 from Community Fibre with your Unifi device, an Ultimate Dream Machine (UDM) in my case, you will have to do some setting tinkering and stay in contact with Community Fibre.

Community Fibre can sometimes have too many MAC addresses registered which "blocks" allowing more to be added to your account. Weird bug but that means you can't get your router to work with IPv6 and you need to contact them to clear them out.

First thing you need to do is enable DHCPv6 and give the router the prefix delegation size which is 48 for Community Fibre. This doesn't seem to be published on their website but is mentioned in a talk they did here with slides here and discussed in this forum post.

You then need to go to the networks you want to have IPv6 and enable it there as well. The settings you want are "Prefix Delegation", enable "Router Advertisement", throw in an IPv6 DNS server of your choice if given the option.

Once you've done all that you now need to do the following:

  1. Reboot their modem and the router
  2. Wait for your router to provide IPv6 addresses to your devices, NB your IPv4 won't work
  3. Disable IPv6 to let the IPv4 work
  4. Re-enable IPv6
  5. Contact community fibre a second time if your router entry in your client's IPv6 settings it blank because the MAC addresses have been blocked again
  6. You're now running on IPv6 (hopefully)