When a proxy provider says "100,000 IPs", the first question that comes to mind is this: how many different blocks do those IPs come from? Because blocking decisions are most often applied not to individual IPs but at the level of IP blocks themselves. If all 100,000 addresses come from a few hundred blocks, your real resilience is not 100,000 but a few hundred.
In this article we look at the concept of the subnet, how block-level blocking works, and how to measure the diversity of a pool.
Subnets and CIDR Notation
IPv4 addresses are 32 bits, and the /n notation states how many of the leading bits make up the "network" part. The remaining bits enumerate the addresses within that network:
| Notation | Number of addresses | Typical use |
|---|---|---|
/32 | 1 | A single address — dedicated proxy |
/29 | 8 | A small corporate allocation |
/24 | 256 | The classic "class C"; the unit of blocking |
/22 | 1.024 | A mid-sized hosting block |
/16 | 65.536 | A large provider allocation |
When the industry talks about "C-class diversity", what is meant is how many different /24 blocks the pool is spread across. This is the practical measure of resilience to blocking.
When a site decides to "block the 185.93.68.0/24 block", all 256 addresses in that block lose access at the same moment.
Why Is Blocking Done at Block Level?
Seen from the defensive side the logic is simple: blocking abusive IPs one by one is both slow and easy to get around, since the attacker just moves to the next address. Blocking the block covers all the neighbours in a single move.
In a concentrated pool, if a single block is blocked a third of your capacity is gone. In a dispersed pool the same event affects only a sixth of it.
Measuring the Diversity of Your Pool
If you have a list of IPs, calculating diversity is simple: take the first three octets of each address and count the unique ones.
The lower the average number of IPs per block, the more resilient the pool. Having all 256 addresses come from the same block is, in practice, like owning a single IP.
An average per block below 10 IPs counts as a good distribution. Above 50, your pool has become concentrated and a single blocking decision creates a large loss.
The Situation Is Different in Residential Pools
Residential pools have high diversity by their very nature, because the IPs come from real home subscribers and are spread across thousands of different ISP blocks. Here the real issue is not the number of blocks but how large the pool genuinely is and how often you get the same IP again.
A simple test: send 200 requests without using the same session key and count how many different exit IPs you see. If the repeat rate is high, the pool is not as large as claimed. Our residential proxy article explains the pool architecture in detail.
The Concept of Diversity Changes in IPv6
In IPv6 the address space is so large that a single customer is usually allocated an entire /64 block — which means many times more addresses than the whole of IPv4. But this abundance is misleading:
In IPv6, changing addresses within the same /64 means "the same source" to most defence systems. Real diversity comes from using different /64 blocks.
For the cost advantage and the limits of IPv6, see our IPv4–IPv6 comparison and IPv6 proxy page.
Questions to Ask When Buying
- How many different /24 blocks is the pool spread across? If no number is given, ask for a small sample and measure it yourself.
- How many different ASNs are used? A single ASN means a single point of failure.
- How many countries are the blocks distributed across? Critical if you are going to do geographic targeting.
- How many customers is the same block shared with? In shared pools your neighbours' behaviour affects you.
- Are blocked blocks replaced? The provider's replacement policy determines your resilience.
Managing Distribution in Your Own Pool
If you buy IPs from more than one provider, add block awareness to your selection logic: spread consecutive requests across different blocks as much as possible. This makes it harder for the target to see the signal of "heavy traffic from the same neighbours".
When a block is blocked, quarantining all the addresses in it together is far more efficient than spending time and quota trying them one by one.
Summary
Pool size on its own is not an indicator of quality; the real determinant is the distribution across blocks and ASNs. Because blocking decisions are most often applied at the /24 level, concentrated pools are fragile. You can measure the list you have with a couple of commands and increase resilience by keeping the average number of IPs per block low. You can verify the liveness and exit locations of your addresses with the proxy checker tool in bulk.