Strange LAN problem.

[alanrf]

Any help or advice on the following would be much appreciated.

I have three Dell computers, all running McAfee.

The computers may be identified as:
1 Vista
2 Win 7
3 Win 7

If I fire up 1, 2 and 3, in that order, each computer can see the other

If I fire up 2 and 3, in either order, then 2 can see 3 but 3 cannot see 2.

I can resolve this issue by turning off the Firewall on 2.  This allows 3 to see 2, and then the Firewall can be turned on and everything is OK - until the next time I fire up.  Setting them to 'trust' each other makes no difference. In fact, is there any real point in 'trusting'?

There are similar issues if I fire up 2 and or 3 before 1, when it is not possible for each computer to see all of the others.  However, if I fire up 1,2 and 3 in that order everything is visible to each computer.

The Firewall configurations on all three computers are, (or appear to be), identical.

Security - is set to Full access

Connections:
- allow access to 192.168.10 - 192.168.1.255
- Security level - Work

Ports and System Services allows:
- Microsoft Directory Server, port 445
- Windows File Sharing, ports 137 - 139
- Network Time Protocol, post 123 (irrelevant here)
- Common Operating Ports, port 5357
- Universal PnP ports 500, 1900, 2869 (irrelevant here)

Network configuration, via Network and Sharing Center ... Change Advanced Settings appear to identical:
- Network discovery - on
- File and printer sharing - on.
- Public folder sharing - on
- File sharing - 128 bit encryption - on
- Password protected sharing - on
- Homegroup connection - on (although neither are in a homegroup because of the 'mixed' OS's on the LAN

[Aldrin]

Sounds like you have covered pretty much everything here. But my only question for you is – These are your Office (or) Home computers? Also have you tried to change the Security Level from Work to Home – if no then please try it and let me know the outcome

[alanrf]

Changing security level from Work to Home made no difference.

However, I followed up further on the Win 7 Help and Support pages, (never thought of that before!), and came across the following info which seems to imply that while Windows Firewall automatically opens the correct ports, third party firewalls may need configuration to allow the following ports:

To find other computers running Windows Vista or Windows 7, open these ports:

UDP 3702, UDP 5355, TCP 5357, TCP 5358

To find other computers running earlier versions of Windows, and to use file and printer sharing on any version of Windows, open these ports:

UDP 137, UDP 138, TCP 139, TCP 445, UDP 5355

To find network devices, open these ports:

UDP 1900, TCP 2869, UDP 3702, UDP 5355, TCP 5357, TCP 5358

Some of these ports are already available via Ports and System Services of course but I tried to add the others.  Adding the port numbers is easy but the configuration also requires the addition of  the following:  System Service Name, System Service Category and Service Description.  The latter is fairly trivial but there is no clear guidance as to what is acceptable, to what would be needed ort acceptable for the other two requirements.

If I can at least try these port settings that may perhaps eliminate the current problem.

This all rather begs the question that McAfee Firewall seems, (or at least tries), to subsume the Windows Firewall and presumably offer equivalent functionality.   On Vista it was possible to re-enable the Windows Firewall but I am unsure whether, or if, this is allowed any more on Win 7.  Clearly this is some sort of McAfee firewall issue as the simple act of temporarily disengaging it resolves the issue.

Any ideas??

[alanrf]

Working just with the two Win 7 boxes, (let's call them Box1 and Box 2 for simplicity),  I have found the following 'oddities'.

Fire up 'Box1' and then fire up 'Box2'. Both are configured as:

Security Level: Full Access

Connections:
- IP Address: 192.168.10 - 192.168.1.255
- Security level: Home.
- IP Address: fe80::/10
- Security level: Home

-----------------------------------------------

Opening the 'Network' link on Windows Explorer provides the following information:

On 'Box1' -

        Computer (2)              Box1, Box2
        Media Devices (2)       Box1
        Network Infrastructure  -

On 'Box2' -

        Computer (1)               Box2
        Media Devices (2)        Box1, Box2
        Network Infrastructure  Router

At this stage 'Box2' cannot see 'Box1' in the Windows  Explorer pane.

-----------------------------------------------

Next step was to turn off the Firewall on 'Box1'

On 'Box1' -

        Computer (2)              Box1, Box2
        Media Devices (2)       Box1
        Network Infrastructure  -

On 'Box2' -

        Computer (1)              Box1, Box2
        Media Devices (2)       Box1, Box2
        Network Infrastructure  -

-----------------------------------------------

Final step was to turn off the Firewall on 'Box2'

On 'Box1' -

        Computer (2)              Box1, Box2
        Media Devices (2)       Box1, Box2
        Network Infrastructure  -

On 'Box2' -

        Computer (1)              Box1, Box2
        Media Devices (2)       Box1, Box2
        Network Infrastructure  -

-----------------------------------------------

After that, both Firewalls can be turned back on and both computers can access each other freely.

There has to be some, possibly obscure, issue with the Firewall settings because once they are turned off inter-computer communication is possible.

[alanrf]

I believe that this issue is now resolved by defining the IP address range in Connections.

The full details are outlined in the thread Firewall on one computer blocks LAN access, dated 12 December 2010, above.