Subnet Calculator / Mission Tech

01 · Configure Your Network

IP Address

. . .

Quick Preset

Prefix Length /24

/0/8/16/24/32

192

168

100

Network bits

Host bits

02 · Live Inspector

CIDR Notation

192.168.1.100/24

Subnet Mask

255.255.255.0

Network Address

192.168.1.0

Broadcast Address

192.168.1.255

First Usable Host

192.168.1.1

Last Usable Host

192.168.1.254

Usable Hosts

254

Network Bits

24 bits

Host Bits

8 bits

03 · Key Concepts

Network Bits

Network bits identify which subnet a device belongs to. Every device on the same subnet shares these bits. Think of them as the street name.

Host Bits

Host bits identify the individual device within a subnet. Network address sets all to 0. Broadcast sets all to 1. Everything between is usable.

Borrowing Bits

Move the slider right by 1 and you borrow one host bit. This doubles your subnets but halves your hosts. Every bit is a trade-off.

Why /24 Everywhere?

A /24 gives 254 usable hosts - enough for any home or small office. It's one full octet for hosts. Your router is almost certainly 192.168.x.0/24 right now.

01 · Configure Your IPv6 Network

IPv6 Address

Quick Preset

Prefix Length /64

/0/16/32/48/64/80/96/112/128

Network prefix

Interface ID

02 · IPv6 Inspector

Full Address

Compressed

Network Prefix

First Address

Last Address

Addresses in Subnet

Prefix Bits

64 bits

Interface ID Bits

64 bits

Address Type

Global Unicast

How to Read an IPv6 Address

An IPv6 address is 128 bits written as 8 groups of 4 hex digits, separated by colons. Each group is called a hextet (16 bits).

2001:0db8:85a3:0000:0000:8a2e:0370:7334

Two shorthand rules make them shorter:

Drop leading zeros in each hextet: 0db8 becomes db8, 0370 becomes 370
Replace one run of all-zero hextets with :: (only once per address): :0000:0000: becomes ::

So the address above compresses to: 2001:db8:85a3::8a2e:370:7334

Prefix vs Interface ID

In IPv6, there is no subnet mask in dotted-decimal form. Instead, you just use CIDR prefix length (the /64 part).

Prefix (network portion): identifies which network the device belongs to. Drag the slider to change it.
Interface ID (host portion): identifies the specific device on that network. In a /64, this is the last 64 bits.

Unlike IPv4, there is no broadcast address in IPv6. Instead, IPv6 uses multicast (ff02::1 for all nodes). Every address in the range is usable.

Common IPv6 Prefix Lengths

/128 - a single host (loopback ::1, or a specific device route)
/64 - the standard subnet. SLAAC (auto-config) requires this. Almost every LAN uses /64.
/48 - typical allocation from an ISP to a customer site. Gives you 65,536 /64 subnets.
/32 - allocation from a RIR to an ISP. 4 billion subnets available to hand out.
/10 - link-local scope (fe80::/10). Auto-assigned on every interface, never routed.
/7 - unique local addresses (fc00::/7, practically fd00::/8). The IPv6 equivalent of RFC 1918 private space.

Key Differences from IPv4

No broadcast - IPv6 uses multicast and anycast instead. No more broadcast storms.
No NAT needed - the address space is large enough (3.4 x 10³⁸ addresses) that every device gets a globally unique address.
Auto-configuration - SLAAC lets devices generate their own address from the network prefix + their MAC (or a random ID). No DHCP required (though DHCPv6 exists).
Simpler headers - fixed 40-byte header, no checksum (handled by link layer), no fragmentation by routers.
No "usable host" math - every address in the range works. A /64 has 2⁶⁴ addresses, all assignable. No -2 like IPv4.

Practice Mode

Test what you know. The bits don't lie.

Question

10.4.12.200/22

What is the network address?