mpd with/without zeroconf (was: access to mpd via trusted uplink.)

[nis65]

Usually, the uplink interface should be locked down as much as possible as the network connected there is out of our own control (e.g. a public access point).

However, when the uplink is connected to a trusted network (e.g. your home network) and you can connect the mpd clients to that same network, direct access to the mpd ports is needed via uplink.

The implementation should be controlled by a Setting in a file, e.g.

UPLINK_TRUSTED=yes

[nis65]

When we are connected to a trusted uplink (via Ethernet and/or External USB WLAN Dongle),

• the uplink should accept mdns (UCP src/dest port 5353) traffic
• the uplink should accept mpd traffic (tcp port 6600)
• if not needed, the WLAN AP should be disabled:
  • at least rfkill on ap0 to free up the radio frequency
  • as a consequence, both hostapd and dnsmasq stop working. Maybe explicity stop?
  • as a consequence, firewalld can be stopped too.
  • edge case: It is probably not wise to connect two uplinks at the same time when firewalld is stopped (and routing is still enabled).

[nis65]

the current mpd config (raspbian default) with enabled mpd.socket does not allow to use mDNS (zeroconf). Enabled zeroconf for test purposes manually by adding two lines to mpd.conf:

zeroconf_enabled               "yes"
zeroconf_name                  "MPD @ %h"

and disabling the systemd mpd.socket (does stop make sense?):

systemctl stop mpd.socket
systemctl disable mpd.socket

This finally gives in mpd.log

avahi: Service 'MPD @ myhostname' successfully established.

See also this discussion which says:

But combining socket activation with zeroconf would be a rather pointless exercise. You would only be able to find MPD after you already connected to MPD.

Ah, indeed, that is a chicken-and-egg.

I believe that I never really use socket activation (as mpd is started on boot and never stopped after), or to be precise: I was always a bit astonished that my mpd kept starting up after a systemctl stop just because one of my tools was polling its state...

So I guess it's safe to disable mpd socket activation to get zeroconf...

What do you @Daenou think about mpd socket activation?

[nis65]

Talking to myself: Well, this is not that a good idea after all. What I want to achieve is to use my standalone camper Pi in the same way as at home (i.e. a plain music device without any routing/secuity requirements. In other words: *Not apply the accesspoint and uplink roles.

So what is left from that feature request (at the moment)

• A script to temporarily disable all features from the accesspoint and uplink roles. It would be nice if ap0 (while not in use by hostapd) could be used again as normal uplink.
• activate zeroconf. This is a completely separate requirement and appears here only as a side effect of me trying to find out what the "real" requirement was/is. Now that I invested a little time into understanding zerconf/mDNS/avahi, this seems to work really well and - besides being a bit noisy on the network - is a good thing as it enables to address devices without a locally managed DNS server (like dnsmasq).

[nis65]

temporarily disable all features...

systemctl stop hostapd
systemctl stop dnsmasq
systemctl stop firewalld

is enough. After a reboot, all is back to normal.

It would be nice if ap0 ... could be used ... as normal uplink.

I don't think that this could be done in a way that reverts automatically on reboot. With the current implementation, it would mean to remove /etc/systemd/system/dhcpcd.service.d/zzoverride.conf "temporarily" and restart dhcpcd. How to ensure that override file is present on next boot again?

[nis65]

Manual stopping is solved (previous comment).

The additional issue (zeroconf) is solved with #71.