IP Addressing: Subnets, CIDR and Private Ranges

What is an IP address

An IP address uniquely identifies a device on a network. Think of it as the device’s postal address: it is what lets packets reach the right destination.

The most common format is IPv4: four octets separated by dots, each between 0 and 255, e.g. 192.168.1.100. An IPv4 address is 32 bits, which allows roughly 4.3 billion unique addresses — far too few for today’s internet. That shortage is why NAT and IPv6 exist.

Subnet masks and CIDR

The subnet mask tells you which part of the address identifies the network and which part identifies the host:

IP:    192.168.1.100
Mask:  255.255.255.0
       ├── network ──┤├host┤

CIDR notation expresses the same thing as a single number: how many bits belong to the network.

Formula: usable hosts = 2^(32 − prefix) − 2, subtracting the network and broadcast addresses. (It applies from /30 up; /31 and /32 are special cases.)

Private vs public ranges

Three blocks are reserved for internal networks (RFC 1918) and are not routable on the internet:

Public addresses are allocated by the regional internet registries (RIPE, ARIN…) and are the ones reachable across the internet. Internal networks use private addresses and reach the internet through NAT.

Key elements of a network

Practical example: subnetting a datacenter

Suppose you have 10.100.0.0/16 available for your datacenter:

10.100.0.0/16 (whole block)
├── 10.100.1.0/24   → VLAN 10: Management (switches, iLO/iDRAC)
├── 10.100.2.0/24   → VLAN 20: Production servers
├── 10.100.3.0/24   → VLAN 30: Storage (iSCSI)
├── 10.100.4.0/24   → VLAN 40: VoIP
├── 10.100.10.0/24  → VLAN 50: DMZ
└── 10.100.100.0/24 → VLAN 100: Monitoring

Each /24 gives you 254 usable addresses — plenty for most segments, and the one-subnet-per-VLAN pattern keeps the design easy to reason about.

IPv6 basics

IPv6 addresses are 128 bits, written in hexadecimal:

2001:0db8:85a3:0000:0000:8a2e:0370:7334
2001:db8:85a3::8a2e:370:7334   (shortened form)

Key advantages: a practically unlimited address space (3.4 × 10^38), built-in autoconfiguration (SLAAC), and no need for NAT. In datacenters, IPv6 is increasingly used for public-facing services, while internal management networks often stay on IPv4 for simplicity.

IP addressing in CreaRack

Every device you register in CreaRack has a management IP address — see [[crearack—racks—dispositivos]]. Observatory uses that IP for SNMP polling and ping checks, and the [[crearack—network—auto-provision-wizard]] discovers devices by scanning an IP range you define. A clean subnetting plan makes both your inventory and your monitoring much easier to organize.

Related

• [[crearack—redes-infra—vlans]] — logical segmentation on top of IP subnets
• [[crearack—redes-infra—switches-routers]] — the equipment that routes between subnets
• [[crearack—redes-infra—monitorizacion]] — polling devices by IP
• [[crearack—racks—dispositivos]] — registering a device’s management IP
• [[crearack—network—auto-provision-wizard]] — discovery by IP range
• [[crearack—monitoring—que-es-observatory]] — IP-based monitoring

Véase también

• [[crearack—redes-infra—vlans]]
• [[crearack—redes-infra—switches-routers]]
• [[crearack—redes-infra—monitorizacion]]
• [[crearack—racks—dispositivos]]
• [[crearack—network—auto-provision-wizard]]
• [[crearack—monitoring—que-es-observatory]]