What Is a Network Address?

Here's an impossible problem: the Internet has billions of devices. Every router needs to know where to send packets. If routers maintained routes to every individual device, the routing tables would be impossibly large, lookups impossibly slow, and the Internet simply couldn't function.

Network addresses solve this. Instead of tracking every device, routers track networks—groups of devices that share a common address prefix. A single routing entry for 192.168.1.0/24 covers 254 possible devices. The router doesn't care about device .100 or device .200. It just knows how to reach the network they're both part of.

Three routing entries. Potentially millions of reachable hosts. That's the trick.

The Two Parts of Every IP Address

Every IP address contains two pieces of information:

• A network portion that identifies which subnet the device belongs to
• A host portion that identifies the specific device within that subnet

Think of it like a street address. "123 Main Street" has two parts: the street name identifies the neighborhood, and the number identifies the specific house. In 192.168.1.100:

• The network portion (192.168.1) identifies the subnet
• The host portion (100) identifies the device

The network address is what you get when you zero out all the host bits. It's the first address in the subnet range—192.168.1.0 in this case. This address is reserved to represent the network itself. No device gets it.

Where the Split Happens

The subnet mask determines the dividing line between network and host bits:

IP Address:    192.168.1.100
Subnet Mask:   255.255.255.0  (/24)
Network Addr:  192.168.1.0
Host Addr:     100

The /24 means the first 24 bits identify the network. The remaining 8 bits can vary for individual hosts. That's 2^8 - 2 = 254 usable addresses. (We lose two: one for the network address, one for the broadcast address at the end of the range.)

Different subnet sizes carve up the space differently:

The /30 is interesting—only two usable addresses. Perfect for a point-to-point link between two routers where you need nothing else.

What Network Addresses Enable

When a device at 192.168.5.50 sends data to 10.20.30.40, here's what happens:

1. The device compares the destination with its own network (192.168.5.0/24)
2. Different network → send to the default gateway
3. The router looks up the destination's network in its routing table
4. It forwards the packet toward that network
5. This repeats until the packet reaches the destination network
6. The final router delivers it to host .40

At every step, decisions are based on network addresses, not individual hosts. A router's table might look like:

Destination       Gateway          Interface
192.168.1.0/24    Local            eth0
10.0.0.0/8        10.10.10.1       eth1
0.0.0.0/0         203.0.113.1      eth2 (default)

Three entries covering potentially millions of destinations.

This also enables route summarization. If you have four networks—192.168.0.0/24 through 192.168.3.0/24—you can advertise them as a single route: 192.168.0.0/22. One entry instead of four. Smaller tables, faster lookups, more stable routing when individual subnets flap.

And it creates hierarchy. You can carve up IP space logically:

Corporate Network: 10.0.0.0/16
├── HQ Building A: 10.0.0.0/22
├── HQ Building B: 10.0.4.0/22
├── Remote Office 1: 10.0.8.0/23
├── Remote Office 2: 10.0.10.0/23
└── Server Farm: 10.0.12.0/22

Each allocation gets its own network address. Easy to route, manage, and secure.

The Boundaries

Network addresses work with broadcast addresses to define subnet boundaries:

• Network address: First address in the range (e.g., 192.168.1.0)
• Broadcast address: Last address in the range (e.g., 192.168.1.255)
• Usable addresses: Everything in between

The network address is the question every packet asks: "Are you one of us?" Same network means talk directly. Different network means ask the router for help.

Common Misconceptions

"The network address is the router"

No. Routers often have addresses like .1 (near the start of the range), but the network address itself (.0 in a /24) isn't assigned to any device. You can't use the network address for a device. It's like trying to live at the street sign.

"Network addresses only matter for big networks"

Even your home network uses them. Your router determines what's local versus what needs to go to your ISP based on network addresses. Every network, no matter how small, has one.

Calculating Network Addresses

To find the network address from any IP and subnet mask, perform a bitwise AND:

IP Address:    192.168.5.175  (11000000.10101000.00000101.10101111)
Subnet Mask:   /26            (11111111.11111111.11111111.11000000)
Network Addr:  192.168.5.128  (11000000.10101000.00000101.10000000)

The network address is 192.168.5.128. The usable range is .129 to .190, with .191 as the broadcast address.

You don't usually calculate this manually—tools handle it:

# Linux/macOS
ip addr show

# Windows
ipconfig /all

But understanding the mechanism helps you design networks, troubleshoot routing issues, and see why certain addresses can't coexist in the same subnet.

Key Takeaways

• Every IP address has two parts: a network portion (which subnet) and a host portion (which device)
• The network address is the first address in a subnet, reserved to identify the network—no device uses it
• The subnet mask determines where the network portion ends and the host portion begins
• Routers make forwarding decisions based on network addresses, enabling the Internet to scale
• Same network address means local communication. Different network address means route through a gateway

Sources

• TCP/IP addressing and subnetting | Microsoft Learn
• Configure IP Addresses and Unique Subnets for New Users | Cisco