Several address ranges are reserved for "Special Use". These addresses all have restrictions of some sort placed on their use, and in general should not appear in normal use on the public Internet. The overview below briefly explains the purpose of these addresses – in general they are used in specialized technical contexts. They are described in more detail in RFC 5735. "Private Use" IP addresses:
10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255 192.168.0.0 - 192.168.255.255
These address blocks are reserved for use on private networks, and should never appear in the public Internet. There are millions of private networks (for example home firewalls often use them). People can use these address blocks without informing us, so we have no record of who uses which of these addresses.
The point of private address space is to allow many organizations in different places to use the same addresses, and as long as these disconnected or self-contained islands of IP-speaking computers (private networks) are not connected, there is no problem. If you see an apparent attack, or spam, coming from one of these address ranges, then either it is coming from your local environment, your ISP, or the address has been "spoofed".
The Private addresses are documented in RFC 1918
. If you have further questions about RFC 1918 usage, please contact your ISP. "Autoconfiguration" IP Addresses
: 169.254.0.0 - 169.254.255.255
Addresses in the range 169.254.0.0 to 169.254.255.255 are used automatically by most network devices when they are configured to use IP, do not have a static IP Address assigned and are unable to obtain an IP address using DHCP.
This traffic is intended to be confined to the local network, so the administrator of the local network should look for misconfigured hosts. Some ISPs inadvertently also permit this traffic, so you may also want to contact your ISP. This is documented in RFC 5735