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?

Answer 1

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

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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