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Firewall/Port information

Posted on 2003-12-09
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Last Modified: 2013-11-16
Hi,
I believe I have an okay understanding of how port numbers work. I just bought a router and firewall software. I need to know how do I configure the firewall, in other words, how do I know which local ports to block to avoid intruders. Thanks for any help on this.
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Question by:bduffy120
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lrmoore earned 1000 total points
ID: 9905462
Most software firewalls block all incoming traffic by default, unless you've specifically requested it. If you're behind a router that is doing NAT (Network address translation), then it is providing a first "shield" to make you virtually invisible to start with. Depending on what all you have on your local LAN, and the software firewall that you have, you might have a checkbox "allow local LAN access" or "allow netbios"
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by:NeilDavis
ID: 9905464
Its easier to block all ports and them open up only the ones you need for mail and internet access.  Your router also may have port filtering which is worth a look.

80 - HTTP - Internet, 110 - pop3 - email etc.  All port numbers are listed here:

http://www.iana.org/assignments/port-numbers

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by:stevenlewis
ID: 9905935
go to www.grc.com and test your sheilds and scan your ports
chances are they are already blocked, and you may be back here asking how to open some (for games, etc)
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by:mikeleebrla
ID: 9912665
inless you are running a www or mail server, do not open port 80 or 110... you will still be able to get to the web and get your mail with these ports closed since your firewall sees that these connections were started from the "inside" and not the "outside" so it will allow them to come thru.   If you do open these ports you will have to do port forwarding to direct them to a particular machine on the inside since what is actually going on is PAT (port address translation).
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