Firewall Rule - TCP and UDP Port 0

[mitchell1981]

Hi,

 

I'm in the process of tidying up our Firewall (a Watchguard XTM device), and removing old rules that I don't think should be there.

 

I've noticed a rule that allows all internal addresses outgoing access on TCP and UDP port 0. I don't really know what this means. If I disable it, then the internet stop working, but I don't think this seems like a normal configuration. I admit my knowledge in this area is not great.

 

Does anyone know why this rule would be there, and why it would prevent internet access when disabled? All I can find about Port 0 is that it is 'reserved'. There are other rules in place allowing 80 and 443 out.

 

Thanks.

[MatthewL]

Disable it and see what breaks, good thing with Watchguard you can do that. Never known anything to use port 0, suspect someone has tried something in the past and never removed it.

[Katy]

At a guess some firewalls might use 0 as a placeholder for "all" hence why disabling it breaks everything... Can you browse to an IP rather than host on ports 80 or 443? If so make sure there's a rule for TCP and UDP 53 allowing DNS out.