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Old 3rd May 2017, 02:53 PM
publius21 Offline
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Join Date: Mar 2010
Posts: 35
Local Name Resolution Problem/Question

This is about a Fedora 25 install I've got running in VM under Virtualbox on Windows. I just installed a Ubuntu 17.01 VM, and I noticed something there that doesn't work in Fedora 25. And that is local link name resolution.

Under the Ubuntu install, it can resolve all the local link names, which include the Windows host and the hostname of my router, plus any other machines on the local link. And for both IPv4 and IPv6.

The Fedora install can't do this. I didn't know it was possible until I installed this Ubuntu version and stumbled onto it. I got to searching around to try to figure out what was going on and learned about the LLMNR protocols, and the systemd-resolve command.

Say the local Windows host is named "foohost" and the router is named "fooroute". Well, under Fedora, systemd-resolve will return the proper IP address, both v4 and v6 for "fooroute", but ping will not work. Ie "ping fooroute" will try something, with the wrong IP4 address, which I think is some public name obtained via DNS. It doesn't respond to pings. Now, "ping -6 fooroute" returns an error "name or service unknown".

So somehow the LLMNR results don't get to the ping command.

Now, trying it with the Windows host, "ping -6 foohost" returns name not found as well. I had put the IP4 address in the "/etc/hosts" file before, and that works of course.

Under Ubuntu 17.04, all the ping commands work, using the LLMNR results as expected.

So, I'm wondering what needs to be adjusted, and where to look for it? :-)
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Old 3rd May 2017, 05:03 PM
publius21 Offline
Registered User
Join Date: Mar 2010
Posts: 35
Re: Local Name Resolution Problem/Question

I found it. It was in the "/etc/nsswitch.conf" file. The Ubuntu system had an extra entry in the hosts line, which inserted a "resolve [!UNAVAIL=return]" string. I assume this tells it to use the "resolve" service, which is where the LLMNR stuff is done.

The whole line is thus this, now:

"hosts: files mdns4_minimal [NOTFOUND=return] resolve [!UNAVAIL=return] dns myhostname"

And it works now in Fedora 25.
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