How Big Is the IP Pool Behind One City and Carrier?

Pick a city and a carrier on our menu and you are not buying one address, you are buying a seat at a pool. Every rotation pulls a new address from that pool, and the obvious question is how many are in there. The honest answer is that it varies by carrier and by region, that repeats are normal, and that you can measure it yourself for the price of a day pass. Here is how the pool works and what the measurements tend to look like.

Where carrier addresses come from

A phone on a US carrier does not get a public address of its own. It gets a private one, and the carrier's gateway translates it to a public address shared with many other phones. That is carrier-grade NAT, and it is the reason a carrier address is trusted: the same address is in use by ordinary subscribers at the same time as you.

The public addresses are grouped into pools that the carrier reserves for a region and a set of gateways. A device in Houston draws from the Texas-area pool of its carrier; a device in Miami draws from the Florida one. The pool is not tied to a tower or a neighborhood, which is why geolocation reads the metro or the state and never anything finer.

When a line rotates, the device drops its data session and starts a new one. The gateway hands it a public address from the same regional pool. It does not choose the least-recently-used address or avoid the one you just had; it picks from what is free, which is why an address can come back after two rotations or after two hundred.

How the three carriers differ

T-Mobile gives up a fresh address readily. Rotate a T-Mobile line in Los Angeles and the new address is almost always different from the last one, and across a day of rotations the set of distinct addresses grows steadily. Its pools tend to be labelled by state rather than by metro in the databases.

Verizon pools are large and tend to hold a session for a long time if you do not rotate. When you do, the new address is usually in a different block of the same regional pool. Verizon addresses are also the ones most consistently labelled with the right metro, which is why we point Boston customers at Verizon.

AT&T sits between the two. Its pools are regional and in some cities they are labelled with the nearest large metro rather than the city the device is in; Boston reading as New York is the clear example on our menu. In Houston, Chicago, Phoenix and Miami, AT&T reads as the city you would expect.

Measuring the pool yourself

A day pass is enough to get a real number for your city and carrier. The method is simple.

• Buy a day pass on the city and carrier you care about, at $4 or $5.
• Write a short loop that calls the rotation link, waits for the device to reconnect, fetches a what-is-my-IP page through the line, and logs the address. There is no waiting period between rotations, but give the modem a moment to come back.
• Run it for an hour or two and count the distinct addresses against the total rotations.
• Look at the ratio of new to repeated addresses over time. Early on nearly every rotation is new; later, repeats appear. Where the curve bends tells you roughly how large the active pool is for that gateway.
• Repeat the test on another carrier in the same city if the first pool looked small. All three carriers are the same price, so switching costs nothing but a few minutes.

What the numbers usually look like

We will not quote a single figure because the pools change and a number printed here would be wrong by spring. What we can say from running the devices is that a few hours of steady rotation on any carrier in any of our eight cities produces far more distinct addresses than anyone needs for a day's work, that repeats begin to show up well before the pool is exhausted, and that the first repeat is not a sign the pool is small, only that assignment is random.

The other thing we can say is that pool size is rarely the real constraint. What matters for most jobs is that each address is a genuine carrier address in the right metro, that the device behind it is yours alone, and that the next rotation is a click away. A pool of thousands that you rotate through blindly is less useful than a pool of hundreds that you rotate through with a plan.

Repeats, and why they are fine

An address coming back is not a defect. Real phones get recycled addresses constantly; the carrier does not care which phone had the address yesterday, and neither do the sites. If a job truly needs an address it has not seen before, log what you have used and rotate again when you hit a repeat; it costs a few seconds and nothing else.

If a job needs more distinct addresses per hour than one pool offers, the move is to add lines rather than to rotate harder. Two day passes on two carriers in the same city give you two pools with no overlap at all, and a third line in another city gives you a third. The menu is designed for exactly that kind of mixing.

What a pool cannot do

A pool cannot make a specific address appear, cannot promise an address that no checker has ever seen, and cannot place you on a particular street. We say this plainly in our terms because no carrier line can do it. If someone needs those things, a carrier line is the wrong tool, and we would rather say so than sell a day pass that disappoints. For everything else, pick a city, pick a carrier, and go see the pool for yourself.

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