Everyday Powershell - Part 37 - Powershell Subnet Scanner

So we had a need to run a subnet scan this morning on a host where installing a subnet scanner would be a hassle. So powershell to the rescue!

Turns out there's a really easy but slow way to do this...
1..254 | ForEach-Object {test-connection ("192.168.6." + $_)}
Then there's a tricky way that's much quicker.

function start-subnetscan{     param(         $addressspace = "192.168.6.",         $startip = 1,         $endip = 254,         $concurrentthreads = 30     )     $report = @()     $startip..$endip | ForEach-Object {         Write-Progress -Activity "Pinging Computers" -Status ("Pinging " + $addressspace + $_.tostring().padleft(3,"0") + " Starting Jobs. Started " + (get-job).count) -PercentComplete (($_ / $endip) * 100)         start-job -scriptblock {             $temp = "" | select IP, Online             $temp.ip = ($args[0] + $args[1].tostring().padleft(3,"0"))             $temp.online = test-connection $temp.ip -Quiet -Count 1             $temp         } -ArgumentList $addressspace, $_           while((get-job).count -ge $concurrentthreads){             Write-Progress -Activity "Pinging Computers" -Status ("Waiting for resources. " + (get-job).count + " jobs running") -PercentComplete (($_ / $endip) * 100)             $report += Get-Job | where state -eq 'completed' | Receive-Job             Get-job | where state -eq 'completed' | Remove-Job         }                                }     $report += get-job | wait-job | Receive-Job     $report | select IP, Online | sort IP | ft     Get-job | wait-job  | Remove-Job }

So to give you an idea of the power of multi threading we setup both commands so we could run them through measure-command and then we raced them!

Measure-Command -Expression {start-subnetscan}  Days              : 0 Hours             : 0 Minutes           : 2 Seconds           : 55 Milliseconds      : 951 Ticks             : 1759513835 TotalDays         : 0.00203647434606481 TotalHours        : 0.0488753843055556 TotalMinutes      : 2.93252305833333 TotalSeconds      : 175.9513835 TotalMilliseconds : 175951.3835 Measure-Command -Expression {1..254 | ForEach-Object {test-connection ("192.168.6." + $_) -count 1}}  Days              : 0 Hours             : 0 Minutes           : 11 Seconds           : 26 Milliseconds      : 940 Ticks             : 6869401183 TotalDays         : 0.00795069581365741 TotalHours        : 0.190816699527778 TotalMinutes      : 11.4490019716667 TotalSeconds      : 686.9401183 TotalMilliseconds : 686940.1183

 

Have a look at that! Running it multi-threaded made it 3 times faster.