Duplicated Windows firewall rules (Netsh AdvFirewall firewall)

Question

I've noticed that when we create a firewall rule through netsh advfirewall firewall, it can be run multiple times, creating multiple identical firewall rules.

Is there any way of checking if the firewall rule exists before attempting to create a new one?

Answer 1

Check if rule "myrule" not exists

netsh advfirewall firewall show rule name="myrule" | findstr "no rules"

Answer 2

I managed to get this going through PowerShell's Network Security Cmdlets, the following code will check for a named firewall rule along with a specified local port, if it finds an entry, it does not create the rule. If it does not find an entry, it will create the rule

$firewallPort = ""
$firewallRuleName = ""

write-host "Checking for '$firewallRuleName' firewall rule on port '$firewallPort' now...."
if ($(Get-NetFirewallRule –DisplayName $firewallRuleName | Get-NetFirewallPortFilter | Where { $_.LocalPort -eq $firewallPort }))
{
    write-host "Firewall rule for '$firewallRuleName' on port '$firewallPort' already exists, not creating new rule"
}
else
{
    write-host "Firewall rule for '$firewallRuleName' on port '$firewallPort' does not already exist, creating new rule now..."
    New-NetFirewallRule -DisplayName $firewallRuleName -Direction Inbound -Profile Domain,Private,Public -Action Allow -Protocol TCP -LocalPort $firewallPort -RemoteAddress Any
    write-host "Firewall rule for '$firewallRuleName' on port '$firewallPort' created successfully"
}