I'm on Community Fibre and had the same problem when TB recognised my IPv6 address, what you need is your IPv4 address and it should only change if there is an outage or they are doing some work on the line, mine has been reporting since 24/09 when they last changed it, I have VOIP via AAISP and they tell me when it changes.

In reply to a post by Moto:

If your router's external IP address is in the range of 100.64.0.0/10 ie begins 100.64. through 100.127. then you are on CGNAT.

To explain CGNAT first consider a normal IPv4 connection.

A domestic router will be allocated a unique IP address. The router provides a private network behind the router with a network range something like 172.16.0.0/24 Millions of domestic installations use the same private network number, private to just them as all communication outside the network is done using the routers allocated public address. The domestic router has to remember which private IP address is expecting what reply so it can translate incoming traffic and pass it on.

Now that there are no new IPv4 addresses to be bought by newer ISPs they have to use IPv6 addresses but IP address ranges cost money. To save money they perform the same Nat process but further up the chain. They allocate a private IPv6 address from that 100.64.0.0/10 range to the outside of your router and all traffic from your router is translated into a unique public IPv6 address further into their network. Unique in that it exists only once on the internet but is being used by multiple customers who all share the same unique IPv6 address.

This means they can use the same private IPv6 address range multiple times across their network. The drawback is that the eventual public IPv6 address is being used by multiple users. A powerful router somewhere on their network is storing information on what traffic is coming from their private network so it can pass back their replies. This results in a small rise in latency which probably goes unnoticed by most users.

If that is right, it is screwed up. The 100.64.0.0/10 range is IPv4, so you cannot allocate an IPv6 address from the range. And the whole point of IPv6 is that there are more than enough addresses to go around without anyone ever sharing. I have available on my network 2^72 IPv6 addresses, all public, compared to 2^32 on the whole internet under IPv4

Nothing of what you describe there has anything to do with IPv6. 100.64.0.0/10 addresses are definitely IPv4.

Thanks for the advice @Moto

Since your message, my external IP abruptly changes to IPv4. The address that was coming up before matches the internal IPv6 address of my laptop. A traceroute to that IPv4 address has a single hop. So it looks like, right now, I'm not on a CGNAT. I possibly was before.

Related, my BQM for my IPv6 address stopped working. I started a parallel one with the new IPv4 address. The quality metrics are night and day. The previous graph was mostly blue and yellow, with packet loss hovering around 5-10%. The new one has a tiny green line at the bottom with no packet loss.

Here's the old BQM from earlier today, looking ropey.

Here's the new BQM, which looks much better.

This coincided with my renewing my contract. I was out of contract on their 40 mbps package (no longer offered) and switched to their 500 mbps one that, bizarrely, is cheaper. Maybe changing the package doesn't just change the bandwidth but the infrastructure too.