An IP address (with IP for Internet Protocol) is an identifier, which is assigned, permanently or temporarily, to each machine connected to a computer network (PC, telephone, smart TV, connected object, ...).
IPv4 (version 4) addresses are 32-bit coded. They are generally represented in decimal notation with four numbers between 0 and 255, separated by dots. Example: 172.16.254.1
A server has as many addresses as there are network cards. Some addresses have a reserved use:
The first bits of the IP address specify the network number, the next bits the host number. The number of bits in the network is specified by the network mask:
When we scan 10.10.10.1/24, we test all addresses from 10.10.10.1 to 10.10.10.255.
192.168.X.X/16, 172.16.0.0/12 and 10.X.X.X/8
The 192.168.X.X/16, 172.16.0.0/12 and 10.X.X.X/8 networks are dedicated to local networks. Such adresses should never be forwarded by routers or boxes to Internet. You must train scans and exploits ONLY on hosts on those networks.
$ ip addr 1: lo:
mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000 loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever 73: eth1@if74: mtu 1500 qdisc noqueue state UP group default link/ether 02:42:0a:0a:0a:03 brd ff:ff:ff:ff:ff:ff link-netnsid 0 inet 10.10.10.3/24 brd 10.10.10.255 scope global eth1 valid_lft forever preferred_lft forever
$ ifconfig eth0: flags=4163
mtu 1500 inet 10.10.0.2 netmask 255.255.255.0 broadcast 10.10.0.255 ether 02:42:0a:0a:00:02 txqueuelen 0 (Ethernet) RX packets 7567 bytes 573298 (559.8 KiB) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 7073 bytes 4046236 (3.8 MiB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0 eth1: flags=4163 mtu 1500 inet 10.10.10.3 netmask 255.255.255.0 broadcast 10.10.10.255 ether 02:42:0a:0a:0a:03 txqueuelen 0 (Ethernet) RX packets 15569 bytes 2618290 (2.4 MiB) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 20985 bytes 1976399 (1.8 MiB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0