How can I check whether an ip address in certain ip range in C#?

See http://stackoverflow.com/questions/2138706/how-to-check-a-input-ip-fall-in-a-specific-ip-range[^] for a number of solutions.

Just split it into the four fields and do some compare operations. You could convert each quad to an integer to help things along.

IP addresses are usually transmitted or typed as strings.
IP as strings can't be compared, you must normalise before comparing.

An IP adress is made of 4 numeric parts with points as separator: "aaa.bbb.ccc.ddd"
1) you have to split the address in its 4 parts.
2) Convert each string part into numeric.
3) Combine them into 1 numeric value NumIP= (( aaa * 256 + bbb ) * 256 + ccc ) * 256 + ddd

Then you can compare numeric values.

Not actual c# code, I let you deal with details.