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I have an Ubuntu box that is connected to the internet and provides ICS.

If I list the open ports by running:

netstat -tulnap | grep LISTEN

it shows me:

tcp        0      0 127.0.0.1:445           0.0.0.0:*               LISTEN      1419/smbd
tcp        0      0 192.168.0.2:445         0.0.0.0:*               LISTEN      1419/smbd
tcp        0      0 127.0.0.1:139           0.0.0.0:*               LISTEN      1419/smbd
tcp        0      0 192.168.0.2:139         0.0.0.0:*               LISTEN      1419/smbd
tcp        0      0 0.0.0.0:5355            0.0.0.0:*               LISTEN      1056/systemd-resolv
tcp        0      0 192.168.0.2:53          0.0.0.0:*               LISTEN      1130/dnsmasq
tcp        0      0 192.168.0.2:22          0.0.0.0:*               LISTEN      1189/sshd
tcp6       0      0 :::5355                 :::*                    LISTEN      1056/systemd-resolv

where, clearly, port 5355 is open on the internet.

Does this open port pose any threat?

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  • Please provide OS/release details, you have tagged an long past end-of-life release so if 17.10 is your release, you may have other unsecured holes in your system.
    – guiverc
    Mar 24 '20 at 8:52
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This is the systemd-resolved that provides network name resolution to local applications via a D-Bus interface. See here

Although I don't quiet get why it is running on a public address. This does not seem to be the default. One could firewall the port or re-configure the service.

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No, it is not a threat.

It is link-local Multicast name resolution provided by systemd. Details are here : https://en.wikipedia.org/wiki/Link-Local_Multicast_Name_Resolution

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  • 2
    Is it required to have that port open for normal network operations?
    – Binar Web
    Mar 24 '20 at 10:27

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