It’s very bad. Here is a list of examples of what I have first hand experience with consumer ISPs doing to fight the shortage of IPv4 addresses:
- Repeatedly shuffling around IPv4 blocks between cities causing brief outages and connection resets for customers.
- Shortening DHCP lease times from days to minutes.
- Allow users to choose if they want network address translation (NAT) on the Customer Premise Equipment (CPE) or not, then retroactively turn it on for everybody anyway.
- Enabling NAT on CPE for customers who already used the opportunity to opt out of NAT.
- Reducing the cap on number of concurrently active media access control (MAC) addresses enforced by CPE.
- Deploying carrier-grade NAT (CGN) for customers who had a real IP address when they signed up for the service.
All of these are reducing the quality of the product the ISP is selling to their customers. The only sensible explanation for why they would be doing this to their customers is shortage of IPv4 addresses.
The shortage of IPv4 addresses has lead to fragmentation of the address space which has multiple shortcomings:
- Administrative overhead which not only costs time and money, but also is error prone and has lead to outages.
- Large usage of content addressable memory (CAM) capacity on backbone routers which a few years back lead to a significant outage across multiple ISPs when it crossed the limit of a particular popular model of routers.
Without NAT there is no way we could get by today with the 3700 million routable IPv4 addresses. But NAT is a brittle solution which gives you a less reliable connectivity and problems that are difficult to debug. The more layers of NAT the worse it will be. Two decades of hard work has made a single layer of NAT mostly work, but we have already crossed the point where a single layer of NAT was sufficient to work around the shortage of IPv4 addresses.