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Troubleshooting networks: Can vendor software self-install firewalls?

Can firewalls block the use of a shared folder after the installation of a router? Our network security expert troubleshoots this wireless connection problem using these steps.

I installed a wireless modem/router: 2Wire. Everything is fine except my users share folders on Computer A. Computer A can successfully ping Computer B, but when Computer B tries to ping Computer A it is not successful.

Computer A has a Windows firewall and B does not. I disabled A's Windows firewall and still B could not ping A. Is it possible that the Norton software (s/w) has installed its own firewall? How do I determine if there's another firewall besides Windows Firewall?

Can you think of any other reasons why, suddenly, after I installed a new modem/router, that previously shared document folders on Computer A cannot be accessed by Computer B?

There could be a number of issues going on here. It could be a Windows networking problem, a configuration issue, or a firewall issue.

Let's start with Windows issues. One good article that might help is on Microsoft's support page: How to troubleshoot network in Windows XP. You will also want to check your TCP/IP settings to make sure IP, netmask, and default gateways are all correct.

If those are correct, check to see if you can you ping by IP and/or computer name. Also, check to see of you can see the other computer in Network Neighborhood. If everything looks right here, check the firewall settings.

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