1

I know there are some IP addresses ranges called "Private IPs" which are used in private networks and are not supposed to be used in public networks like Internet. I also read another question in this forum where is clearly stated you just can't use them in those types of networks.

Nevertheless I'm still wondering what stops you from do that. Why it's not possible to give a private IP address to a device which you are going to expose on the Internet? Is just that the ISP won't ever give you such a type of IP? Couldn't it be set manually some way?

ela
  • 151
  • 2

2 Answers2

1

The companies on the Internet, including any ISPs, have agreed not to route packets using certain address ranges, including the Private IP address ranges.

In any case, a device with any IP address needs to connect to another device in that network. If you simply put a Private address on your device, it will not match the network on the ISP, so you cannot communicate with the ISP. Your device and the ISP router to which it connects must share a network.

Ron Maupin
  • 102,040
  • 26
  • 123
  • 202
1

IP does not have a concept of "public" or "private". An address is an address, although there are various special use addresses defined in RFC's. What makes an address "private" is community agreement not to route them, at least globally.

Just as you can use RFC1918 address blocks however you want within your own network -- even spanning the globe -- so can any other network, including an ISP. Most (if not all) ISPs do use "private" addresses within their own network. It's generally frowned upon to have those blocks exposed to internet facing systems, but from time to time they are. (i.e. you should not be able to traceroute to any of those addresses.)

[Technically, you can do whatever you want with ANY address blocks. Using global addresses internally will just result in those parts of the actual internet being unreachable.]

Ricky
  • 32,810
  • 2
  • 45
  • 85