Adding only real MAC address

Question

During the course of the work day I have field techs out and about and they'll occasionally need to add a MAC address to our Wireless Access group in AD. We don't fully support them getting into AD on their own and we've been using a script to allow them to add MAC addresses the right way. I have taken it upon myself to fully idiot-proof this thing and i'm nearly there minus one glaring issue. I can't stop them from adding MAC addresses with values greater than 'f'.

Write-Host "MAC Address must be entered as lowercase and without colons. EX: 14d6aa6ac9be" -ForegroundColor Yellow
    $MACUserName = Read-Host -Prompt 'Please Input the MAC Address of the Device to be added to AD and press Enter'
    $MACUserName = $MACUserName -replace '[\W]', ''
    If ($MACUserName.Length -ne 12 -or $MACUserName -notmatch '[A-Za-z0-9]') {
        Write-Host "MAC Address: " -ForegroundColor Red -NoNewline; Write-Host $MACUserName -ForegroundColor White -NoNewline; Write-Host " is not the correct length or contains invalid characters. Please verify MAC address" -ForegroundColor Red
        Pause
        Single-Device}

This is where i'm at with everything so far, obviously there is much more to this than just this section but for now this is where i live.

I'm able to get rid of any colons that might be entered in and my -notmatch section includes all possible values.

if i change -notmatch '[A-Za-z0-9]' to -notmatch '[A-Fa-f0-9]' It still lets me add fake MAC addresses with z's and whatnot. How do I go about limiting the characters this section will accept?

user_15339544 · Answer

I think you should be able to leverage the .NET PhysicalAddress Class for this. You can create a function to parse the user's input:

function ParseMAC {
    param(
        [Parameter(ValueFromPipeline)]
        [string] $MacAddress
    )

    process {
        try {
            [pscustomobject]@{
                ParsedMAC = [PhysicalAddress]::Parse($MacAddress.ToUpper().Replace(':', '-'))
                UserInput = $MacAddress
            }
        }
        catch {
            Write-Warning 'Invalid MAC Address!'
        }
    }
}

Read-Host 'input mac address' | ParseMAC

Example of how it works:

PS /> ParseMac 01-23-45-67-89-AB

ParsedMAC    UserInput
---------    ---------
0123456789AB 01-23-45-67-89-AB

PS /> ParseMac 001122334455

ParsedMAC    UserInput
---------    ---------
001122334455 001122334455

PS /> ParseMac f0:e1:d2:c3:b4:a5

ParsedMAC    UserInput
---------    ---------
F0E1D2C3B4A5 f0:e1:d2:c3:b4:a5

PS /> ParseMac 00112233445z

WARNING: Invalid MAC Address!

Note: The use of .ToUpper().Replace(':', '-') in the function is required to make it compatible with .NET 4.x and previous versions.

Valid Formats from Remarks of PhysicalAddress.Parse(String):

001122334455
00-11-22-33-44-55
0011.2233.4455
00:11:22:33:44:55
F0-E1-D2-C3-B4-A5
f0-e1-d2-c3-b4-a5

user_45375 · Answer

Santiago Squarzon's helpful answer offers the best solution to your problem, using a .NET API.

As for what you tried:

'[A-Fa-f0-9]' matches one character that falls into the specified ranges, which means that one such character in the input string makes the expression evaluate to $true - even if other characters outside these ranges are present.

Therefore you must make sure that all characters that make up the input string fall into the expected ranges:

-notmatch '^[a-f0-9]+$'

Alternatively, invert the logic and look for at least one invalid character:

-match '[^a-f0-9]'

Note:

The -match / -notmatch operators perform substring matching by default; therefore, in order to match the entire string, start and end anchors ^ and $ are needed.
[a-f] is enough to match both lowercase and uppercase letters, because -match / -notmatch are case-insensitive by default, as PowerShell is in general. If case-sensitive matching is desired, use -cmatch / -cnotmatch

Adding only real MAC address

2 Answers