Jump to content
Search In
  • More options...
Find results that contain...
Find results in...

what are /30 /29....?

i) what are those things in red?

ii) how do he know it has 4 IP address, 8 IP address..... are those a standard which cant be modified? or can be calculated when ip changes?


Link to post
Share on other sites

They are called CIDR, just a short handed form of identifying the Subnet Mask. 

PSU Tier List Thread

Please make sure to Quote me or Tag me to see your reply!


"White Ice"

Ryzen 7 3700x | Asus Crosshair VIII Hero (Wi-Fi) | EVGA RTX 2080ti | Ballistix 32gb 16-18-16-36 3600mhz | Custom Water Cooling Loop | 1tb Samsung 970 Evo

2tb Crucial MX500 SSD | 2x 3tb Seagate Drive | Fractal Design Meshify S2 |  EVGA G2 750w PSU | 3x Corsair LL140 | 3x Corsair LL120


Dedicated Streaming Rig

 Ryzen 7 1800x | Asus B450-F Strix | 32gb Gskill Flare X 3000mhz | Corsair RM550x | EVGA GTX 1060 3gb | 250gb 860 Evo m.2

Phanteks Enthoo Evolv |  Elgato HD60 Pro | Elgato 4k60 Pro mk.2 | Avermedia 4k GC573 Capture Card


Link to post
Share on other sites

As @Skiiwee29 said, they are a shorthand form of the subnet mask. It gets tiresome to write all the time. So instead, you write /24 instead. Why 24?


Your subnet mask is basically a bit-mask. If you were to write in binary, it would be 11111111.11111111.11111111.00000000, that is a total of 24 1s (so /24). While would be 11111111.11111111.11111111.11111100 or 30 1s (so /30).


This is also a hint why /30 results in 4 possible IP addresses: Every bit of your IP address that matches with a "1" in the subnet mask is fixed. Every bit that matches a "0" can be modified. Which means with a subnet mask of /30 you have a total of two bits you can modify. Two bits have four possible values: 00, 01, 10, 11.


Another example:








The subnet mask tells you that the first three octets can't be modified, while the last octet is variable. Your last octet has 8 bits so 2^8 possible values (=255). So your network has a total of 255 possible IP addresses.


Any IP address that does not match the bits of the "fixed part" of your IP address belongs to a different network. So e.g. would be part of your network while would not.

Remember to quote or @mention others, so they are notified of your reply

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now