IP Address Lookup
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Understanding IP Addresses
An IP (Internet Protocol) address is a unique numerical identifier assigned to every device connected to a network. It serves two primary functions: host identification and location addressing. There are two versions of IP addresses in use today.
IPv4 vs IPv6
| Feature | IPv4 | IPv6 |
|---|---|---|
| Format | Four decimal octets (e.g. 192.168.1.1) | Eight hex groups (e.g. 2001:0db8::1) |
| Address Size | 32-bit (~4.3 billion addresses) | 128-bit (~3.4 × 1038 addresses) |
| Example | 10.0.0.1 | fe80::1 |
| Header Size | 20-60 bytes | 40 bytes (fixed) |
| NAT Required | Often yes | No (enough addresses) |
Private IP Address Ranges (RFC 1918)
| Range | CIDR | Number of Addresses | Class |
|---|---|---|---|
| 10.0.0.0 – 10.255.255.255 | 10.0.0.0/8 | 16,777,216 | Class A |
| 172.16.0.0 – 172.31.255.255 | 172.16.0.0/12 | 1,048,576 | Class B |
| 192.168.0.0 – 192.168.255.255 | 192.168.0.0/16 | 65,536 | Class C |
CIDR Notation Quick Reference
CIDR (Classless Inter-Domain Routing) notation specifies an IP address and the number of leading bits in the subnet mask. For example, 192.168.1.0/24 means the first 24 bits define the network, leaving 8 bits (256 addresses) for hosts.
| CIDR | Subnet Mask | Addresses | Usable Hosts |
|---|---|---|---|
| /32 | 255.255.255.255 | 1 | 1 |
| /30 | 255.255.255.252 | 4 | 2 |
| /28 | 255.255.255.240 | 16 | 14 |
| /24 | 255.255.255.0 | 256 | 254 |
| /16 | 255.255.0.0 | 65,536 | 65,534 |
| /8 | 255.0.0.0 | 16,777,216 | 16,777,214 |
Special IP Addresses
| Address | Purpose |
|---|---|
| 127.0.0.1 | Loopback (localhost) |
| ::1 | IPv6 loopback |
| 0.0.0.0 | Unspecified / all interfaces |
| 255.255.255.255 | Broadcast (local network) |
| 169.254.x.x | Link-local (APIPA) |
| 224.0.0.0 – 239.255.255.255 | Multicast |