When you open a website, three quiet services make it look easy: your device gets an address, it resolves a name, and it sends packets to the right place. Almost every network investigation starts with one of them.
IP addresses
An IPv4 address is 32 bits, written as four decimal octets: 192.168.1.24. Each octet is 0–255.
An IPv6 address is 128 bits, written in hexadecimal: 2001:db8::1a2b. The :: collapses one run of zero groups.
Some IPv4 ranges are reserved for private networks:
| Range | Common use |
|---|---|
10.0.0.0/8 | Large private networks, cloud VPCs |
172.16.0.0/12 | Private networks (172.16–172.31) |
192.168.0.0/16 | Home and small office networks |
127.0.0.0/8 | Loopback (127.0.0.1 is your own machine) |
Private addresses are not routable on the public internet. Your router translates them through NAT, which we will cover in the next lesson.
Subnets and CIDR
The /24 in 192.168.1.0/24 is the prefix length: the number of leading bits that identify the network. The remaining bits identify hosts.
/24leaves 8 host bits: 256 addresses, 254 usable after the network and broadcast addresses./16leaves 16 bits: 65,536 addresses./32is a single host.
A device also needs a default gateway (usually the router) and one or more DNS servers. Without the gateway, it can talk on the local network but not beyond it.
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