C-Class IP Hosting: What It Means and Why It's Not Enough for a PBN

At a glance

• “C-class IP hosting” means hosting where each site gets an IP with a different third number (a different C-block), so the sites don’t look like neighbors on one network.
• IP classes are history. The internet replaced classful addressing with CIDR, specified in RFC 1519 in 1993, so “C-class” in SEO is a leftover name.
• A C-block is the first three numbers of an IPv4 address, and it holds 256 addresses, 254 of them usable by hosts.
• Different C-blocks bought from one seller usually sit on one provider’s network, with the same owner (ASN) and often the same custom nameservers. That shared ownership is what ties the sites together.
• Real diversity means different hosting companies, different owners of the IP space, and nameservers that thousands of unrelated sites also use.

What “C-class” means, and why the term is outdated

An IPv4 address is four numbers from 0 to 255, separated by dots. Each number is 8 bits, called an octet.

	Octet 1	Octet 2	Octet 3	Octet 4
Example IP	162	149	205	185
What SEOs call it	A-block	B-block	C-block	the host
Same C-block as 162.149.205.188?	same	same	same	different

The old classes

In the original addressing plan, the leading bits of an address decided its class, and the class decided how big the network was. RFC 4632 (fetched 2026-10-28 from rfc-editor.org) summarizes it: Class A had 128 possible networks of 16,777,216 addresses each, Class B had 16,384 networks of 65,536, and Class C had 2,097,152 networks of 254 usable hosts each.

Class	Leading bits	First octet	Network size
A	0	0 to 127	16,777,216 addresses
B	10	128 to 191	65,536 addresses
C	110	192 to 223	254 usable hosts
D	1110	224 to 239	Multicast, not assigned to sites
E	1111	240 to 255	Reserved

The first-octet ranges follow from the leading bits. Class D was later defined for multicast, and the rest of that space stayed reserved, per the same RFC.

CIDR replaced classes

The class system ran out of room. Class C was too small for most organizations and Class B was too big, and routing tables were growing faster than routers could handle. The fix was Classless Inter-domain Routing (CIDR), specified in RFC 1519 in September 1993 and updated by RFC 4632 in 2006. RFC 4632 notes that “As of 2005, CIDR has been thoroughly deployed.”

Under CIDR, a network can be any size, written as an address and a prefix length. A /24 is the old Class C size: the first 24 bits (three octets) are fixed, and the last octet varies. That’s 256 addresses, minus the all-zeros and all-ones addresses, which leaves 254 for hosts.

So when someone sells you “C-class IPs”, what they mean is IPs in different /24 ranges, with a different third octet. The address 162.149.205.185 isn’t “a Class C IP” in any modern sense (its first octet would have made it Class B under the old rules). It just lives in the C-block 162.149.205. Our PBN guide calls this out too: C-block hosting is “commonly mis-categorized as ‘C-Class’”. We use “C-block” for the rest of this article.

IPv6, by the way, doesn’t change any of this for PBN builders. It uses 128-bit addresses, a space vastly larger than IPv4, and almost all of the conversation about hosting footprints is still about IPv4.

What C-class IP hosting is, and why it caught on

C-block hosting started from a reasonable idea. Sites on sequential IPs in the same C-block usually sit on the same network, often the same server, and are assumed to belong to the same owner. If a set of blogs that all link to one site share a C-block, that relationship is cheap for anyone to spot.

SEOs noticed that sites with links from many different C-blocks tended to do well, and concluded that C-block diversity mattered. Whether Google counts it directly was never settled. What’s clear is that a cluster of linking sites in one C-block is the first thing anyone checking for a network would look at.

Hosting sellers responded with “unique C-class IP” packages. The economics favored them: a small host can buy or lease a number of /24 ranges cheaply and spread customer sites across them. The customer sees different third octets, and the package says “diverse IPs.”

Why unique C-blocks aren’t enough

Different third octets hide very little. If you look up who owns each IP, a “diverse” set of C-blocks bought from one seller usually tells one story.

Same owner. IP ranges on the public internet are announced by networks identified by an Autonomous System Number (ASN). Look up the ASN of ten IPs from one cheap C-block host and you’ll often find one or two organizations behind all of them. Our post on ASN footprints shows how to check.

Same provider. The same hosting company, the same data centers, often the same server range. A network that looks diverse in the third octet still points back to one place.

Sequential IPs. Some hosts hand out IPs in order, so the fourth octets of your sites line up neatly.

Custom nameservers. Many classic SEO hosts run their own nameservers, used only by their customers. Our PBN guide calls this out directly: use nameservers given by the hosting providers, not nameservers unique to the PBN host, because unique nameservers are a big footprint. More on that in nameserver footprints.

Reputation. Our /seo-hosting/ page puts it this way: “Even if you do everything right, IPs that differ only in the C-block have gained a poor reputation due to their misuse.” Ranges sold as SEO hosting fill up with other people’s networks, and some of those get burned.

Our guide puts hosting that varies only the C-block in the “neutral footprint” category: not enough on its own to get a network deindexed, but the links can be discounted, because Google expects links to come from a diverse range of IPs. In our experience, bad hosting is one of the most common reasons PBNs get deindexed, and hosting that is diverse only on paper is a big part of that.

What real IP diversity looks like

A natural set of sites doesn’t look like ten addresses from one seller. It looks like ten unrelated sites that happen to have picked different hosts. That means:

• Different hosting companies, each with its own IP space, so the ASNs differ.
• IPs in different A-, B- and C-blocks, so the first and second octets vary as well as the third.
• Nameservers from the hosting provider or from a large DNS provider, shared with thousands of unrelated sites.
• One site per IP, so no two blogs in your network share an address.
• Non-sequential IPs, even when two sites end up with the same provider.

You can check any site yourself. Look up its IP, then run a whois or ASN lookup on that IP to see which organization owns the range. Do the same for its nameservers. If most of your sites resolve to one owner, the C-block diversity isn’t hiding anything. If your sites sit behind Cloudflare, check that the real IPs don’t leak, which our research on Cloudflare IP leaks found to be common.

A-blocks matter too. We cover them in their own post on A-class IP hosting.

What our 2016 cheap-host IP analysis found

A common piece of advice for new PBN owners is to spread blogs across many cheap hosting accounts to get IP diversity. In 2016 we tested it.

We collected 80 popular budget hosting providers recommended in forums and Facebook groups and checked who owned the IPs their own websites ran on, using the ASN method above. The 80 hosts’ IPs were owned by just 17 companies. One hosting group, which had bought up many hosting brands, owned more than a third of them. Only about 20% of the hosts looked like they ran their own servers.

The reason is simple. Most cheap hosts don’t own servers, IPs or data centers. They rent servers or reseller plans from bigger providers and put every customer there. There’s nothing wrong with that for an ordinary website. But if you open 80 hosting accounts and manage 80 logins for diversity, you’re paying for far less of it than you think.

This is dated, first-party data from 2016. We haven’t repeated it, so treat the exact numbers as a snapshot. The method still works, and it’s worth running on any host before you sign up.

How Easy Blog Networks handles it

We built Easy Blog Networks around the gaps above. If you want to host every blog on its own IP, here is what that looks like:

• Each blog gets a unique IP with one of many large hosting providers, including Amazon Web Services, DigitalOcean, Linode, Rackspace and IBM Cloud. The full list is on our providers page.
• Nameservers come directly from the hosting provider. For providers without their own, we use popular DNS providers that serve tens of thousands of other websites.
• All IPs are in different A- or B-blocks, or at the very least non-sequential C-blocks.
• You can use up to 500 unique IPs, out of a pool of a few thousand. That means an average user has access to less than 5% of the pool.
• Per our FAQ, the pool spans 38 A-blocks, all from providers in the US, UK, Canada and Australia.

That’s also how we differ from classic SEO hosting, which is explained on our SEO hosting page: we do the job SEO hosting promised, but on the providers’ own IPs and nameservers. For the wider question of what SEO hosting is, see what SEO hosting is, and for everything else that can tie blogs together, read about PBN footprints.