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Test if IPs are in same subnet

Hello, today this is not a post about Windows Azure, but an old little function to test if an ip is in the same subnet as another ip.

How it works ? Well, we have 3 functions, the two first are here to be used locally, and the function you’ll have to use to test is Test-IsInSameSubnet.

#How to use it

Test-IsInSameSubnet -ip1 192.168.0.12 -ip2 172.16.0.234 -mask 255.255.255.0
False

Test-IsInSameSubnet -ip1 192.168.0.12 -ip2 192.168.0.13 -mask 255.255.255.128
True

Here is the main code…

function Get-BroadcastAddress {
    param (
        [IpAddress]$ip,
        [IpAddress]$Mask
    )

    $IpAddressBytes = $ip.GetAddressBytes()
    $SubnetMaskBytes = $Mask.GetAddressBytes()

    if ($IpAddressBytes.Length -ne $SubnetMaskBytes.Length) {
        throw "Lengths of IP address and subnet mask do not match."
        exit 0
    }

    $BroadcastAddress = @()

    for ($i=0;$i -le 3;$i++) {
        $a = $subnetMaskBytes[$i] -bxor 255
        if ($a -eq 0) {
            $BroadcastAddress += $ipAddressBytes[$i]
        }
        else {
            $BroadcastAddress += $a
        }
    }

    $BroadcastAddressString = $BroadcastAddress -Join "."
    return [IpAddress]$BroadcastAddressString
}

function Get-NetwotkAddress {
    param (
        [IpAddress]$ip,
        [IpAddress]$Mask
    )

    $IpAddressBytes = $ip.GetAddressBytes()
    $SubnetMaskBytes = $Mask.GetAddressBytes()

    if ($IpAddressBytes.Length -ne $SubnetMaskBytes.Length) {
        throw "Lengths of IP address and subnet mask do not match."
        exit 0
    }

    $BroadcastAddress = @()

    for ($i=0;$i -le 3;$i++) {
        $BroadcastAddress += $ipAddressBytes[$i]-band $subnetMaskBytes[$i]

    }

    $BroadcastAddressString = $BroadcastAddress -Join "."
    return [IpAddress]$BroadcastAddressString
}

function Test-IsInSameSubnet {
    param (
        [IpAddress]$ip1,
        [IpAddress]$ip2,
        [IpAddress]$mask
    )

    $Network1 = Get-NetwotkAddress -ip $ip1 -mask $mask
    $Network2 = Get-NetwotkAddress -ip $ip2 -mask $mask

    return $Network1.Equals($Network2)
}

Hope it’ll help you!

See ya 🙂

If you wan to use the # source code version it’s here