IP Addresses

Every device on a network needs an address — otherwise packets can't find it. The IP address is that address.

IPv4: the classic

192.168.1.50

Four numbers, 0–255, separated by dots. Each number is one byte (8 bits), so the whole address is 32 bits — about 4 billion possible addresses. That sounded like plenty in 1981. It wasn't, which is why the rest of this chapter exists.

Your address right now (typical home network):

ip -brief addr

Check (verified shape, typical addresses):

lo               UNKNOWN        127.0.0.1/8 ::1/128
eth0             UP             192.168.1.50/24 ...

(The /24 is the subnet — next chapter.)

Private vs. public

Only some IPv4 addresses route on the internet. Three ranges are private — free for any home/office network, never valid on the public internet:

Range	Typical use
10.0.0.0 – 10.255.255.255	Large networks
172.16.0.0 – 172.31.255.255	Medium networks
192.168.0.0 – 192.168.255.255	Home networks (your router uses one)

Your laptop is probably 192.168.1.x. Your router has two addresses: a private one facing your home (192.168.1.1) and a public one facing the internet (assigned by your ISP). It translates between them — that's NAT, covered in Your LAN.

Special addresses worth knowing

Address	Meaning
127.0.0.1	localhost — "this computer." Always works, needs no network
0.0.0.0	"All interfaces" — a server listening here accepts from anywhere
255.255.255.255	Broadcast — "everyone on my local network"

Check (verified):

ping -c 2 127.0.0.1

2 packets transmitted, 2 received, 0% packet loss

localhost always answers — it's the simplest possible network test.

IPv6: the successor

IPv4's 4 billion addresses ran out (workarounds like NAT delayed the crisis for decades). IPv6 uses 128 bits — 340 undecillion addresses, enough for every grain of sand to have a network:

fe80::70dc:7cff:fe34:2ffd

Eight groups of hex, with :: compressing runs of zeros. Your devices almost certainly have IPv6 addresses already; most home traffic still uses IPv4, and everything in this guide works for both unless noted. You don't need to master IPv6 to run a home network — just recognize the format when you see it.

Next: Subnetting in 10 Minutes