0

I've just finished reading up about IP addresses and subnets through this Cisco article.

In the examples provided by the article, IP addresses seem pretty arbitrary.

This got me thinking, why are the default IP addresses for most home networks 192.168.0.1/24? Is there a reason (historic or otherwise) for the apparent convention of "192.168.0"?

Additionally, are there any implications if I decided I wanted to change my home network's IP address to something arbitrary and easier to type like 1.1.1.1/24?

ptk
  • 127
  • 1
  • 8
  • @MichaelHampton thanks for the link. I found your response an amazing read. You may mark my question as a duplicate of that thread if you wish. Thanks again for sharing (and for taking the time to write that fantastic response). – ptk Jan 28 '21 at 22:41
  • You can do it yourself by clicking a button that should be showing above, that says something like "This solved my problem". – Michael Hampton Jan 28 '21 at 22:45

1 Answers1

5

There are Special-Purpose IP Addresses (RFC 6890) and Internet addresses registered to specific owners (IANA IPv4 Address Space Registry). For private networks you can (only) use private addresses:

  • Private IPv4 addresses (RFC 1918)
    • 10.0.0.0/8 (10.0.0.0 – 10.255.255.255)
    • 172.16.0.0/12 (172.16.0.0 – 172.31.255.255)
    • 192.168.0.0/16 (192.168.0.0 – 192.168.255.255)
  • Unique Local IPv6 Unicast Addresses fc00::/7 (RFC 4193)

If you configure your private network to use 1.1.1.0/24 you would be using IP addresses currently registered to the APNIC and Cloudflare DNS Resolver project and break connectivity with that address space, containing e.g. the 1.1.1.1 DNS service from Cloudflare.

In the article, Cisco does not set a good example on how to use public IP addresses in examples, either. There are IPv4 Address Blocks Reserved for Documentation (RFC 5737; 192.0.2.0/24, 198.51.100.0/24 & 203.0.113.0/24), but Cisco is using arbitrary addresses belonging to someone else. Don't be like Cisco.

Community
  • 1
Esa Jokinen
  • 1,619
  • 10
  • 11
  • 1
    This does not address the WHY - which is "obvious" - it is the first small (/24) network and obviously one engineer follows the next and all end up using the same private address space. – TomTom Jan 28 '21 at 10:16
  • @TomTom: That's true, but also the given example `1.1.1.1/24` (instead of e.g. `192.168.123.0/23`) demonstrates the lack of understanding the private networks, not the *why*. – Esa Jokinen Jan 28 '21 at 16:36