0.0.0.0/0
Public0.0.0.0/0 is the default route, representing all IPv4 addresses. In routing tables it is the "route of last resort." In security groups and firewall rules it means "allow all IPs" — use with caution.
Network address — the base address of the block (0.0.0.0). All devices in this subnet share this prefix. Cannot be assigned to a host.
Broadcast address — packets sent to 255.255.255.255 are delivered to every device in the subnet. Also reserved — not assignable.
Usable hosts — the 4,294,967,294 addresses between those two that you can assign to servers, VMs, or interfaces.
Subnet mask — 0.0.0.0 is the dotted-decimal equivalent of /0. Older tools and Cisco configs use this format instead of CIDR slash notation.
Full Details
| CIDR Notation | 0.0.0.0/0 |
| Network Address | 0.0.0.0 |
| Broadcast Address | 255.255.255.255 |
| Subnet Mask | 0.0.0.0 |
| Wildcard Mask | 255.255.255.255 |
| Prefix Length | /0 |
| IP Address Class | Class A |
| Total IP Addresses | 4,294,967,296 |
| Usable Host Addresses | 4,294,967,294 |
| First Usable IP | 0.0.0.1 |
| Last Usable IP | 255.255.255.254 |
| Network (Hex) | 0x00000000 |
| Broadcast (Hex) | 0xFFFFFFFF |
| Address Type | Public / Globally Routable |
Binary Representation
The first 0 bits (1s in the mask) identify the network. The remaining 32 bits identify hosts within the network.
Subnet Breakdown — splitting into /1
This /0 block can be divided into 2 /1 subnets.
| CIDR | Network | Broadcast | First Usable | Last Usable | Hosts |
|---|---|---|---|---|---|
| 0.0.0.0/1 | 0.0.0.0 | 127.255.255.255 | 0.0.0.1 | 127.255.255.254 | 2,147,483,646 |
| 128.0.0.0/1 | 128.0.0.0 | 255.255.255.255 | 128.0.0.1 | 255.255.255.254 | 2,147,483,646 |
Common Use Cases
- → Default gateway route (route of last resort)
- → Security group rule meaning "allow all IPs"
- → VPN split tunneling — force all traffic through VPN
- → BGP route advertisement of a full routing table