Net+ -- Private Address Classes... Just A Suggestion?
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In the 'IP Addressing' episode of the CompTIA Net+ course it was mentioned that there are three different classes of internal (non-public) IP addresses:
RFC 1918
Private Addresses reserved for internal use
Not registered with IANA
Class A
10.0.0.0 - 10.255.255.255
Subnet Mask: 255.0.0.0
# Networks: 1
# Hosts per network: 16,777,214
Class B
172.16.0.0 - 172.31.255.255
Subnet Mask: 255.240.0.0
# Networks: 16
# Hosts per network: 65,534
Class C
192.168.0.0 - 192.168.255.255
Subnet Mask 255.255.0.0
# Networks: 256
# Hosts per network: 254
Sure enough my Linksys router is using class C, but this got me thinking. Are home networks really forced to only use these three private address classes? As I understand it your local home IPs will go to your router when they want to access the internet. The router then keeps track of which of your 'home IPs' requested what, and retrieves the requested data using a single public IP (NAT). So if your home IPs always remain hidden from your ISP; what if anything is preventing you from using 45.0.0.1 inside your home network? Will your router just refuse to route local traffic out because it knows you're using a public IP and it is only configured to accept those three private class IPs?
Apologize if this question has been posted before. Figured it would be best to get help with this thought before proceeding further in the course. :) -
Deren,
Thanks for writing in. Most routers, even the low cost consumer grade routers, will let you choose whatever network you would like for the internal network. Technically there is nothing stopping you from choosing 45.0.0.0/8 for your internal network if you want as long as you NAT your internal systems to the external IP of the router on their way out. If you disable NAT then your ISP will drop your packets as unroutable. The only problem you will bump into is that if you deviate from the RFC 1918 ranges then you will be selecting a real public IP range that someone else is most likely using. That will mean that systems on your local network will be unable to access any internet services hosted in that same range because they will think the servers are local. The main problem there is that you have no way of knowing who uses that IP range. It's obviously not recommended, but it would work.
Hope that helps,
Don Pezet
Host, ITProTV