Ok class, time for Networking 101.
The internet runs on an addressing protocol called TCP/IP, which contains, obviously TCP & IP, and some other protocols like Telnet & FTP.
The current iteration of TCP/IP is TCP/IP Version 4. In TCP/IP V4 the address (ex. 192.168.100.100) is actually a 32-bit binary number converted to a easy to read format that is broken down into the following classes.
Class A: 1.0.0.0 to 126.0.0.0
Class B: 128.0.0.0 to 191.255.0.0
Class C: 192.0.0.0 to 223.255.255.0
Class D: 224.0.0.0 to 239.255.255.255
Not Used - Multicast AddressesClass E: 240.0.0.0 to 255.255.255.254
Not Used - Experimental AddressesAn ISP has to apply to a licencing body & request a block of addresses to use so they can hand them out to you when you connect to the internet, but you might not ever get one of these addresses as your ISP might assign you a "Private" IP address & automaticaly translate it to a public IP address when your data goes through their system.
Ok class, confused yet?
Each used class has a range of addresses that are considered "private". This means that all networking appliances (Modems, routers, ect.) will not send any traffic with these addresses out onto the internet. The private ranges for the A, B, & C ranges are:
Class A: 10.0.0.0 to 10.255.255.255 (Max - 16.7 Million Addresses)
Class B: 172.16.0.0 to 172.31.255.255 (Max - 1,048,544 Addresses)
Class C: 192.168.0.0 to 192.168.255.255 (Max - 65,024 Addresses)
These are the addresses that you will recieve depending on how your network or your ISP is configured. There is a protocol called DHCP (Dynamic Host Configuration Protocol) that will go out and look for a DHCP Server & get all of the information that you computer needs to connect to the network like your IP address, DNS servers, Subnet Mask & Default Gateway. If you do a Release & Renew on your network card, you might get a new IP address from the DHCP server & that is why your address is changing.
Ok class, take a break & have a beer. Next time, Networking 201 - Subnetting
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