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I'm trying to secure my internet browsing. I just reinstalled Xubuntu 14.04 and GUFW firewall. I have 8 UDP ports open. I don't understand why. The software I currently have open are Firefox, GUFW, Mousepad, Ubuntu Software Center, Software Updater and Terminal. Would any of these correspond with the open software? When I installed GUFW its introduction said it installs with no open ports as well as Ubuntu. The applications related to the open ports are avahi-daemon, dhclient, and cups-browsed. I'd rather close them if they're not needed.

Instructions on closing them via GUFW or Terminal would be appreciated as I am a novice.

I can attach a screen print if needed.

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avahi-daemon

Avahi is a low-level service discovery mechanism. It tends to be used by all kinds of random things, so there's no way I can tell you exactly who is using it, and for what.

Short of pulling out the packet sniffer and going hunting, your choices are basically to just live with it or disable the whole service and see what breaks.

dhclient

This is the DHCP client. It needs to receive UDP packets on port 68. If your computer uses DHCP to configure its networking, you need to keep this open.

If you don't use DHCP on that computer, you can simply remove dhclient entirely.

cups-browsed

CUPS is the printing subsystem of your Linux distro. You can remove this service, but that will mean your GUI won't be able to find new printers when they appear on the network. You'll have to go back to the bad old days of manually typing in IP addresses.

(Unless it's a Bonjour printer, in which case it will be picked up by Avahi. Printer discovery is just one of the many things Avahi can do, however. Don't get the idea that these two services are mutually redudant. Avahi's wide footprint just happens to overlap CUPS a bit in this area.)

I wouldn't worry about this service. It isn't tied into anything really sensitive.

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