array IndexOf IPv4 subnets

Hi

I have an array of subnets like

PS C:\> $Subnet2update

Subnet         
------         
10.255.77.0/24
10.255.78.0/24
10.255.152.0/24
10.255.157.0/24
10.255.158.0/24
10.9.44.0/23   
10.9.46.0/23   
10.9.34.0/23   
10.9.50.0/24   
10.255.237.0/24
10.9.48.0/23   
10.9.32.0/23   
10.9.36.0/23   
10.9.51.0/24   
10.9.40.0/24   
10.9.39.0/24   
10.9.38.0/24   
10.9.41.0/24   
10.9.59.0/24 

I like to find the index of a subnet in the array

[array]::IndexOf($Subnet2update,10.9.48.0/23) but it give me always a False

What do I wrong? (PS version is 5.1 on Win10)

Is it because I'm working with IPv4 addresses?