What Is an IP Address Range? How Networks Are Segmented

What an IP Address Range Is and Why It Matters

An IP address range is a contiguous block of IP addresses that share the same network prefix. Every network, from a home Wi-Fi router to a major cloud provider's data center, is defined by a range. Routing tables, firewall rules, access control lists, and geographic IP databases all operate on ranges rather than individual addresses. Understanding how ranges work is a prerequisite for subnetting, network design, and any serious security configuration.

In modern networking, IP ranges are expressed in CIDR notation (Classless Inter-Domain Routing), which compactly encodes both the network address and the number of significant prefix bits. A range written as 192.168.1.0/24 means the first 24 bits are the network prefix, and the remaining 8 bits identify individual hosts within that range. This gives you 256 total addresses (192.168.1.0 through 192.168.1.255), of which 254 are usable for hosts (the first is the network address and the last is the broadcast address).

How IP Ranges Are Calculated

The subnet mask is the other way to express a range boundary. A /24 corresponds to the subnet mask 255.255.255.0. A bitwise AND of any address in the range with the subnet mask produces the network address. For example:

• 192.168.1.75 AND 255.255.255.0 = 192.168.1.0 (the network address)
• The broadcast address is the network address with all host bits set to 1: 192.168.1.255
• Usable host range: 192.168.1.1 through 192.168.1.254

The number of usable host addresses in a range is always 2^(32 - prefix_length) - 2. For a /24 that is 2^8 - 2 = 254. For a /16 that is 2^16 - 2 = 65,534.

Reserved IP Ranges and Their Purposes

Not all IP ranges are available for public use. Several blocks are permanently reserved by IANA (Internet Assigned Numbers Authority) for specific functions:

• 10.0.0.0/8 — Private use (RFC 1918). Over 16 million addresses for internal networks.
• 172.16.0.0/12 — Private use (RFC 1918). Covers 172.16.0.0 through 172.31.255.255, approximately 1 million addresses.
• 192.168.0.0/16 — Private use (RFC 1918). The most common home and small office range.
• 127.0.0.0/8 — Loopback. Traffic sent to any address in this range stays on the local host and never reaches the network. 127.0.0.1 is the standard localhost address.
• 169.254.0.0/16 — Link-local (APIPA). Automatically assigned when DHCP fails. Used by Windows and Linux for local discovery when no DHCP server responds.
• 100.64.0.0/10 — Shared address space (RFC 6598). Used by ISPs for Carrier-Grade NAT (CGNAT) between customer equipment and the provider network.
• 0.0.0.0/8 — This network (unspecified). Cannot be used as a source or destination in routed traffic.
• 255.255.255.255/32 — Limited broadcast. Reaches all hosts on the local segment; not routed by any router.

How Public IP Ranges Are Assigned

The global pool of publicly routable IPv4 addresses is managed hierarchically. IANA allocates large blocks (typically /8s or /16s) to five Regional Internet Registries (RIRs):

• ARIN — North America
• RIPE NCC — Europe, Middle East, Central Asia
• APNIC — Asia-Pacific
• LACNIC — Latin America and Caribbean
• AFRINIC — Africa

RIRs then allocate smaller blocks to ISPs, enterprises, universities, and cloud providers. Those organizations announce their ranges to the global BGP routing table as prefixes, making them reachable from anywhere on the internet. You can query which organization owns a specific range using the WHOIS protocol or databases like the ARIN registry or BGPView.

Subnetting: Splitting Ranges for Network Design

Subnetting takes a large range and divides it into smaller sub-ranges for organizational or security purposes. A /16 range can be split into 256 /24 subnets, each serving a different department, VLAN, or security zone. Common subnetting use cases include:

• Departmental isolation: Engineering uses 10.1.1.0/24, Finance uses 10.1.2.0/24, and Guest Wi-Fi uses 10.1.3.0/24. Firewall rules between subnets enforce access policies.
• Data center segmentation: Web servers, application servers, and database servers each live in separate subnets. Database servers have firewall rules accepting connections only from the application server subnet.
• VLAN mapping: Each VLAN typically maps to a distinct IP subnet. The Layer 2 and Layer 3 boundaries align, simplifying both switching and routing configurations.

Common IP Range Sizes Reference

Common Misconceptions

The /24 is always right for a home or small office network

A /24 gives 254 usable host addresses, which is more than almost any home or small office will use. Most home networks have fewer than 20 devices. A /27 (30 usable hosts) or /28 (14 usable hosts) is often sufficient, though in practice the overhead of calculating a tighter range for a home network rarely justifies the effort. In enterprise environments, right-sizing subnets avoids wasting address space and reduces broadcast domain size.

Ranges from different ISPs never overlap

Private ranges (RFC 1918 space) absolutely overlap. Your 192.168.1.0/24 at home is identical to the 192.168.1.0/24 on thousands of other home networks globally. They do not conflict because they are never routed on the public internet. This is also why site-to-site VPNs between companies that both use 10.0.0.0/8 require NAT—to resolve the overlap.

All addresses in a range are usable

No. The first address (network address) and last address (broadcast address) in any subnet are reserved and cannot be assigned to hosts. A /24 has 256 total addresses but only 254 assignable host addresses. This distinction matters when calculating how many devices a subnet can serve.

A larger range prefix number means more addresses

The opposite is true. A larger prefix number means more bits are fixed as the network prefix, leaving fewer bits for host identification. A /8 has more addresses than a /24 because it has fewer fixed bits and more flexible host bits.

Pro Tips for Working With IP Ranges

• Use ipcalc or sipcalc for subnet math. Don't calculate binary by hand under pressure. Tools like ipcalc 192.168.5.0/25 instantly return the network address, broadcast, usable range, and host count. The online calculator at subnet calculator sites works equally well.
• Document your IP allocation plan before deploying. Assigning ranges ad hoc leads to overlapping subnets, firewall gaps, and routing ambiguity. Maintain an IP address management (IPAM) record—even a spreadsheet—showing which range maps to which function.
• Summarize routes whenever possible. If you have four /24 subnets at 10.1.0.0/24, 10.1.1.0/24, 10.1.2.0/24, and 10.1.3.0/24, a single 10.1.0.0/22 summary route covers all of them. Fewer, larger prefixes in routing tables mean faster lookups and simpler configs.
• Check BGP announcements for your range. Use tools like bgp.he.net or BGPView to verify that your organization's IP ranges are being announced correctly and are not being leaked by other ASes. Unauthorized prefix announcements (BGP hijacks) are a real threat.
• Plan for IPv6 alongside IPv4 ranges. IPv6 subnets are conventionally sized at /64 for endpoint segments, giving more than 18 quintillion host addresses per subnet. Allocate /48s per site and /64s per VLAN to stay compatible with SLAAC (Stateless Address Autoconfiguration).
• Firewall rules should reference ranges, not individual IPs. Using a /24 or /22 in a firewall rule is more maintainable than listing 50 individual host addresses. When a new server is added within that range, it is automatically covered.

IP ranges are the organizational foundation of every network. Getting them right—right-sized subnets, clean documentation, properly announced BGP prefixes—prevents cascading problems in routing, security, and troubleshooting. Find out which IP range your address belongs to here.