Every device on a network needs an address. On the internet, that address is an IP address. It's just a number, but it tells packets where to go and where they came from. This article covers what an IP address is, how IPv4 addresses are written and grouped into subnets, and the public vs private distinction that matters most for IoT.
This is the parent page for the IP-addresses topic. Two child articles go deeper:
IPv4 addresses, in plain English
IPv4 addresses are 32-bit numbers. To make them readable, the 32 bits are split into four 8-bit chunks (called octets) separated by dots. Each octet is a number from 0 to 255.
That's an IPv4 address. Four numbers, each in the range 0 to 255, separated by dots. The full IPv4 address space runs from 0.0.0.0 to 255.255.255.255, which is about 4.3 billion addresses in total.
You may also see addresses written in CIDR notation, which adds a slash and a number:
The /24 is the subnet mask. It says "the first 24 bits identify the network, the rest identify hosts within the network". So 192.168.1.0/24 describes 256 addresses from 192.168.1.0 through 192.168.1.255.
Common subnet sizes:
| CIDR | Network bits | Host bits | Number of addresses |
|---|---|---|---|
/32 | 32 | 0 | 1 (a single host) |
/30 | 30 | 2 | 4 |
/24 | 24 | 8 | 256 |
/16 | 16 | 16 | 65,536 |
/8 | 8 | 24 | 16,777,216 |
/0 | 0 | 32 | All of IPv4 |
/32
/30
/24
/16
/8
/0
Public vs private IP addresses
The same 4.3 billion addresses split into two camps:
| Type | Reachable from the internet? | Examples |
|---|---|---|
Public | Yes (globally unique) | The IP your home router has on the internet side; the IP a server hosts a website on |
Private | No (only inside one network) |
|
Public
Private
Private IP ranges are reserved by the IETF for use inside private networks. Many networks can use the same private IP at the same time without conflict, because their devices aren't reachable from each other directly.
How Simbase assigns IPs to SIMs
By default, every Simbase SIM gets a private IPv4 address when it attaches to the network. The address is assigned dynamically (DHCP) by the Simbase gateway, and it may change between attaches.
Because the SIM has a private IP, it sits behind NAT at the Simbase gateway. This means:
The SIM can initiate outbound connections to your servers, to APIs, to the wider internet.
The SIM cannot be reached inbound. Your servers can't open a connection to the SIM directly.
This is the right default for most IoT deployments. It's secure (no exposed surface), it conserves IPv4 space, and the device-initiated request/response pattern fits 99% of use cases.
When you need a Public IP
Assign a Public IP to a SIM when:
You need to SSH or HTTP into the device from your laptop or a server.
You're running a VPN endpoint on the device.
You're using a server-initiated protocol that needs to push to the device (rare in modern designs).
The device is a remote camera, gateway, or router you need to access on demand.
Public IPs are assigned per SIM in the dashboard. They're billed daily. See Public IPs for the configuration steps and pricing implications.
Common questions
Yes. Private IPs are assigned dynamically when the SIM attaches, so the address can differ between sessions. If you need a stable address, assign a Public IP or use a private network.
Not with the default private IP, the SIM sits behind NAT and can't accept inbound connections. Assign a Public IP to the SIM, or place it on a private network, if you need to reach the device.
That's a private IP from the Simbase gateway, which is the default for every SIM. It's expected, not a fault. The address is only meaningful inside Simbase's network, not on the public internet.
No. Simbase SIMs are assigned IPv4 addresses only. Set the device's IP type to IPv4 rather than IPv6 or dual-stack.
Related
Private vs public IP address, what's reachable from the internet
Network Address Translation (NAT), how one public address serves many SIMs
Public IPs, assign a routable address to a SIM
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