C# - Check if one or more variables are equal to each other

I have 10 variables :

public string ipAddress1;
public string ipAddress2;
public string ipAddress3;
public string ipAddress4;
public string ipAddress5;
public string ipAddress6;
public string ipAddress7;
public string ipAddress8;
public string ipAddress9;
public string ipAddress10;

I want to check if one of them is equal to another. If so, I want to show an error message to prevent the user to use two identical Ip Address.

I could use multiple if statement like :

if (ipAddress1 = ipAddress2 || ipAddress3 || ipAddress4 || ipAddress5 || ipAddress6 || ipAddress7 || ipAddress8 || ipAddress9 || ipAddress10)   

But I'm shure there's another way.