How do you get mdns working?

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How do you get mdns working?

Richmond
I have changed the domain names of two systems to .local, and on both
systems:

I have the service avahi-daemon running (and /usr/sbin/avahi-dnsconfd -s).

I have enabled the Bonjour service in the firewall.

I have

 hosts:      files mdns_minimal [NOTFOUND=return] dns

in /etc/nsswitch.conf

But if I ping computer2.local or computer2 it does not recognize the name.

How do I get this working?


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Re: How do you get mdns working?

Freek de Kruijf
Op dinsdag 5 december 2017 09:18:34 CET schreef Richmond:

> I have changed the domain names of two systems to .local, and on both
> systems:
>
> I have the service avahi-daemon running (and /usr/sbin/avahi-dnsconfd -s).
>
> I have enabled the Bonjour service in the firewall.
>
> I have
>
>  hosts:      files mdns_minimal [NOTFOUND=return] dns
>
> in /etc/nsswitch.conf
>
> But if I ping computer2.local or computer2 it does not recognize the name.
>
> How do I get this working?

With just a few systems in your network is using /etc/hosts to assign names to
IP addresses much easier.

--
fr.gr.

Freek de Kruijf
menber openSUSE


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Re: How do you get mdns working?

Carlos E. R.-2
In reply to this post by Richmond
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On Tuesday, 2017-12-05 at 08:18 -0000, Richmond wrote:

> I have changed the domain names of two systems to .local, and on both
> systems:

Notice that the .local domain name is incompatible with using Samba to
connect to a Windows Server Domain.

- --
Cheers,
        Carlos E. R.
        (from openSUSE 42.2 x86_64 "Malachite" at Telcontar)

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Re: How do you get mdns working?

Jan Ritzerfeld-3
In reply to this post by Richmond
Am Dienstag, 5. Dezember 2017, 08:18:34 CET schrieb Richmond:
> I have changed the domain names of two systems to .local, and on both
> systems:

Where did you change the domain name? In general, you don't need to change the
domain name of your system to use mdns. It's work in addition to your existing
domain name, even if you didn't specify any domain name.

> I have the service avahi-daemon running (and /usr/sbin/avahi-dnsconfd -s).

Does the output of "systemctl status avahi-daemon" indicate that you are
actually joining the mDNS multicast groups? Do you find any system using
"avahi-browse --all"?

> I have enabled the Bonjour service in the firewall.

When I had the SuSEfirewall2 enabled it blocked all incoming mDNS requests. So
did you check the firewall's log files?

> I have
>
>  hosts:      files mdns_minimal [NOTFOUND=return] dns
>
> in /etc/nsswitch.conf

Looks like the default.

> But if I ping computer2.local or computer2 it does not recognize the name.

Try resolving both host names via "avahi-resolve-host-name" on both systems.
At least "avahi-resolve-host-name computer1.local" should work on computer1
and "avahi-resolve-host-name computer2.local" on computer2.

> How do I get this working?

Well, sometimes it simply does not work. I've seen WiFi routers and repeaters
that somehow kill mDNS. Besides the obvious: the firewall on the target.

Gruß
 Jan
--
Ninety percent of everything is bullshit.


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Re: How do you get mdns working?

Richmond
I got it working! (Well, on two out of three). And...

Jan Ritzerfeld wrote:Does the output of "systemctl status avahi-daemon"
indicate that you are
> actually joining the mDNS multicast groups? Do you find any system using
> "avahi-browse --all"?
This gave the first clue. On one computer this listed out its own
hostname with both ipv4 and ipv6, but on the other it listed nothing.

So...

>
> Well, sometimes it simply does not work. I've seen WiFi routers and repeaters
> that somehow kill mDNS. Besides the obvious: the firewall on the target.
>
>

I switched the computer which listed nothing from wlan0 to eth0. Then it
listed itself, but only with ipv4, not ipv6.

So I disabled ipv6 on both computers, and it all started working.

However, adding a third computer wasn't so good. Although it appeared on
the avahi-browse -a of the first two, it listed nothing itself. I am not
sure why it is at the moment, but that third computer is on 42.2, so
needs upgrading anyway. Maybe that will fix it.

Danke schön.

Thanks to the others who replied too.


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Re: How do you get mdns working?

Jan Ritzerfeld-3
Am Dienstag, 5. Dezember 2017, 20:37:01 CET schrieb Richmond:
> I got it working! (Well, on two out of three). And...

Fine! BTW, I looked into /etc/sysconfig/SuSEfirewall2.d/ and saw that there is
indeed services/avahi. Some years ago, SuSEfirewall2 blocked the incoming
answers when using ping but not avahi-resolve:
https://lists.opensuse.org/archive/opensuse-security/2008-09/msg00011.html

> [...]
> I switched the computer which listed nothing from wlan0 to eth0. Then it
> listed itself, but only with ipv4, not ipv6.

Does "systemctl status avahi-daemon" show lines like this?
Dec 06 17:59:04 karl avahi-daemon[1124]: Joining mDNS multicast group on
interface wlan0.IPv6 with address fe80::xxxx:xxxx:xxxx:xxxx.

> So I disabled ipv6 on both computers, and it all started working.

Strange. Maybe the WiFi router or access point blocks IPv6 multicast groups?

> [...]
> However, adding a third computer wasn't so good. Although it appeared on
> the avahi-browse -a of the first two, it listed nothing itself.

So, it gets the requests from the other two computers and can respond but
cannot send its own requests or receive the related responses. You could use
iptraf or wireshark on the first and third computer to check what happens on
"avahi-browse -a" issued on the third.

> I am not
> sure why it is at the moment, but that third computer is on 42.2, so
> needs upgrading anyway. Maybe that will fix it.

Besides the SuSEfirewall2 issue, I've been using mDNS successfully for about
ten years. At the moment, I am using it on 42.2 for accessing my NAS and
printer via IPv4 and IPv6.

> Danke schön.
> [...]

Gern geschehen!

Gruß
 Jan
--
You have not converted a man because you have silenced him.


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Re: How do you get mdns working?

James Knott
On 12/06/2017 12:51 PM, Jan Ritzerfeld wrote:
> Strange. Maybe the WiFi router or access point blocks IPv6 multicast groups?

WiFi access points are effectively an Ethernet bridge and like a
bridge/switch are supposed to pass all valid Ethernet frames, regardless
of content.  Routers don't pass multicasts, unless specifically
enabled.  There are methods for a device to request a router pass a
specific multicast address.  The router in turn will do the same to the
next upstream router, etc..  However, some multicasts such as mDNS are
for the local link only and not passed through any router.


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Re: How do you get mdns working?

Jan Ritzerfeld-3
Am Mittwoch, 6. Dezember 2017, 13:12:41 CET schrieb James Knott:
> On 12/06/2017 12:51 PM, Jan Ritzerfeld wrote:
> > Strange. Maybe the WiFi router or access point blocks IPv6 multicast
> > groups?
> WiFi access points are effectively an Ethernet bridge and like a
> bridge/switch are supposed to pass all valid Ethernet frames, regardless
> of content.

Yes, they are supposed to. Unfortunately, not all APs offer correct multicast
bridging even not using IPv4. It's sad. One of my repeaters got a faulty
firmware update once that stopped multicast bridging. I had to wait for
another update.

> Routers don't pass multicasts, unless specifically
> enabled.  There are methods for a device to request a router pass a
> specific multicast address.  The router in turn will do the same to the
> next upstream router, etc..  However, some multicasts such as mDNS are
> for the local link only and not passed through any router.

You're right: mDNS is local like broadcast and, thus, there is no real routing
involved.

Gruß
 Jan
--
Ambition is a poor excuse for not having enough sense to be lazy.


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