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My PC: W10 Pro v1909 build 18363.778 i7-8700k processor on Asus ROG Strix Z-370e MB

On VirtualBox v6.0.20 I have Linux 19.3 Cinnamon (Tricia) installed.

I need to allow traffic from Cinnamon to W10 PC by creating an inbound rule. I need to know 1. If I need rules for both ports 139 (NetBios) and 445 (SMB) 2. Do I need rules for both incoming and outgoing? 3. Should the rule(s) specify TCP or UDP or both?

Any help appreciated, out of my depth here a bit as this is my 1st VirtualBox/Linux experience.

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  • I created an incoming TCP and UDP rule for both ports. No difference, still cant reach a shared folder on Linux 19.3 from PC
    – Drocks
    Commented Apr 20, 2020 at 0:34
  • Um, so which system is the one serving the shared folder and which system is the one trying to access it? Your comment says it's on the Linux system, but your main post says the opposite...
    – grawity_u1686
    Commented Apr 20, 2020 at 7:27

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If I need rules for both ports 139 (NetBios) and 445 (SMB)

Port 445 should be enough.

Modern systems (post-Win2000) always try port 445 first, and in fact SMBv3 (the modern protocol version) is only specified to run over port 445. The only time you might need port 139 is for very old SMBv1 clients (such as Windows 98).

For SMBv1 the two ports act as alternatives: 445 is direct SMB over TCP, whereas 139 uses an intermediate "NetBIOS Session Service" wrapper, but ultimately they provide the same SMBv1 service.

Do I need rules for both incoming and outgoing?

On a stateful firewall (which is most of them), you only need a rule that matches the initial connection – the firewall will automatically allow the data flow in both directions.

So the machine serving the share usually needs only an inbound rule.

Should the rule(s) specify TCP or UDP or both?

SMB always uses TCP.

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