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I just ran nMap against my IP address and got the following result:

  • PORT STATE SERVICE
  • 21/tcp open ftp
  • 22/tcp open ssh
  • 23/tcp open telnet
  • 80/tcp open http
  • 443/tcp open https
  • 3389/tcp open ms-term-serv

Which of these are ok to have open, which aren't? If I close 80 and 443 will this afftect my ability to browse the net? Will closing 21 affect my ability to connect to FTP sites etc etc or does closing a port only affect inbound connections?

Thanks

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3 Answers 3

up vote 4 down vote accepted

Assuming you scanned from outside your network, nmap is showing you what you're listening on. It only affects inbound. You can close the ports.

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Thanks for the help! –  JMK Feb 13 '12 at 20:04

I completely agree with mgjk. This traffic is external --> internal traffic. It will not affect any outbound connections that you make.

I just wanted to add one thing to his information. These ports are going to come into play if you do any sort of remote management/access to your system and/or port forwarding. Also, depending on the type of internet you have. These may be ports that are open on your cable/DSL modem for your ISP to access the device. So you may not be able to close these ports at all. I know if I scan my home IP, it shows a lot of ports that are truly not open through my firewall.

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Like the other answers, it depends on what you scanned and where you scanned it from.

If this is your personal computer and you scanned it from your local network or scanned localhost from your own machine, then you shouldn't probably have any of those open unless you are serving on those ports.

If this is some sort of a server (which it doesn't look like from your question), then probably its is legitimately offering those services.

If its your personal computer, I am intrigued as to why are these services open at the very first place. Since you are listening on 80, did you try putting your IP address on the browser to see what comes up. It is pretty normal for a bot to install lightweight http/ftp/smtp servers on infected machines and serve content, send emails etc.

Just try putting your IP on the browser address bar to see if there are any surprises in waiting !!

To answer your question, your ability to browse internet will not be affected if you close these ports.

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