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#1 2021-11-04 00:02:13

mwigzell
Member
Registered: 2016-01-29
Posts: 26

[SOLVED] How do I debug my avahi/mdns setup?

I had a working network printer, but now the "avahi-browse" is not returning any devices on my ".local".
I did find that there was an issue with "firewalld" but I have since disabled it. I do have a vpn (nordvpn) installed, but stopping it doesn't help.

(base) mark@confucius:etc$ sudo pacman -Q avahi
avahi 0.8+22+gfd482a7-1
(base) mark@confucius:etc$ sudo pacman -Q nss-mdns
nss-mdns 0.15.1-1
(base) mark@confucius:etc$

My /etc/nsswitch.conf hosts line:

hosts: files mymachines myhostname mdns_minimal [NOTFOUND=return] resolve [!UNAVAIL=return] dns

My avahi-daemon status:

(base) mark@confucius:etc$ systemctl status avahi-daemon
● avahi-daemon.service - Avahi mDNS/DNS-SD Stack
     Loaded: loaded (/usr/lib/systemd/system/avahi-daemon.service; enabled; vendor preset: disabled)
     Active: active (running) since Wed 2021-11-03 14:39:18 PDT; 2h 6min ago
TriggeredBy: ● avahi-daemon.socket
   Main PID: 232185 (avahi-daemon)
     Status: "avahi-daemon 0.8 starting up."
      Tasks: 2 (limit: 38369)
     Memory: 1.2M
        CPU: 45ms
     CGroup: /system.slice/avahi-daemon.service
             ├─232185 "avahi-daemon: running [confucius.local]"
             └─232186 "avahi-daemon: chroot helper"

Nov 03 14:39:18 confucius avahi-daemon[232185]: No service file found in /etc/avahi/services.
Nov 03 14:39:18 confucius avahi-daemon[232185]: *** WARNING: Detected another IPv4 mDNS stack running on this host. This makes mDN>
Nov 03 14:39:18 confucius avahi-daemon[232185]: Joining mDNS multicast group on interface enp4s0.IPv4 with address 192.168.86.43.
Nov 03 14:39:18 confucius avahi-daemon[232185]: New relevant interface enp4s0.IPv4 for mDNS.
Nov 03 14:39:18 confucius avahi-daemon[232185]: Joining mDNS multicast group on interface lo.IPv4 with address 127.0.0.1.
Nov 03 14:39:18 confucius avahi-daemon[232185]: New relevant interface lo.IPv4 for mDNS.
Nov 03 14:39:18 confucius avahi-daemon[232185]: Network interface enumeration completed.
Nov 03 14:39:18 confucius avahi-daemon[232185]: Registering new address record for 192.168.86.43 on enp4s0.IPv4.
Nov 03 14:39:18 confucius avahi-daemon[232185]: Registering new address record for 127.0.0.1 on lo.IPv4.
Nov 03 14:39:19 confucius avahi-daemon[232185]: Server startup complete. Host name is confucius.local. Local service cookie is 171>

When I run 

 avahi-browse --all --ignore-local --resolve --terminate

and in another terminal I am already running 

 sudo tcpdump port 5353

I see:

(base) mark@confucius:etc$ sudo tcpdump port 5353
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on enp4s0, link-type EN10MB (Ethernet), snapshot length 262144 bytes
16:56:16.515323 IP confucius.mdns > 224.0.0.251.mdns: 0 [3q] PTR (QM)? _services._dns-sd._udp.local. PTR (QM)? _mpd._tcp.local. PTR (QM)? _device-info._tcp.local. (81)
16:56:16.526887 IP 192.168.86.90.mdns > 224.0.0.251.mdns: 0*- [0q] 2/0/7 PTR _spotify-connect._tcp.local., PTR _sonos._tcp.local. (708)
16:56:16.531160 IP 192.168.86.31.mdns > 224.0.0.251.mdns: 0*- [0q] 2/0/7 PTR _spotify-connect._tcp.local., PTR _sonos._tcp.local. (708)
16:56:16.567816 IP HomeShare.mdns > 224.0.0.251.mdns: 0*- [0q] 2/0/0 PTR _rsp._tcp.local., PTR _daap._tcp.local. (84)
16:56:16.598044 IP HomeShare.mdns > 224.0.0.251.mdns: 0*- [0q] 5/0/0 PTR _workstation._tcp.local., PTR _afpovertcp._tcp.local., PTR _adisk._tcp.local., PTR _http._tcp.local., PTR _wd-2go._tcp.local. (161)
16:56:16.598602 IP 192.168.86.45.mdns > 224.0.0.251.mdns: 0*- [0q] 1/0/0 PTR _sonos._tcp.local. (66)
16:56:16.629482 IP 192.168.86.42.mdns > 224.0.0.251.mdns: 0*- [0q] 2/0/0 PTR _airplay._tcp.local., PTR _spotify-connect._tcp.local. (99)
16:56:16.644650 IP brother_printer.mdns > 224.0.0.251.mdns: 0*- [0q] 7/0/0 PTR _pdl-datastream._tcp.local., PTR _printer._tcp.local., PTR _ipp._tcp.local., PTR _scanner._tcp.local., PTR _http._tcp.local., PTR _privet._tcp.local., PTR _uscan._tcp.local. (203)
16:56:16.644817 IP6 fe80::dee9:94ff:fe36:92e0.mdns > ff02::fb.mdns: 0*- [0q] 7/0/0 PTR _pdl-datastream._tcp.local., PTR _printer._tcp.local., PTR _ipp._tcp.local., PTR _scanner._tcp.local., PTR _http._tcp.local., PTR _privet._tcp.local., PTR _uscan._tcp.local. (203)
16:56:16.646318 IP 192.168.86.32.mdns > 224.0.0.251.mdns: 0*- [0q] 3/0/0 PTR _ssh._tcp.local., PTR _workstation._tcp.local., PTR _sftp-ssh._tcp.local. (115)

My /etc/hosts has "brother_printer" line:

192.168.86.50	brother_printer

Therefore I know that the printer at 192.168.86.50 is sending a reply to the "avahi-browse", but still, nothing is reported from the "avahi-browse" line above. Totally empty result.
This was working in early October. recently I updated my packages with no incident, and it hasn't worked since then.
running 

sudo nmap -sU

on my ip address:

Nmap scan report for ?.?.?.?
Host is up (0.0000090s latency).
Not shown: 996 closed udp ports (port-unreach)
PORT     STATE         SERVICE
68/udp   open|filtered dhcpc
137/udp  open          netbios-ns
138/udp  open|filtered netbios-dgm
5353/udp open          zeroconf

Nmap done: 1 IP address (1 host up) scanned in 1.31 seconds

How to debug further?

Last edited by mwigzell (2021-11-04 18:21:15)

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#2 2021-11-04 00:39:35

tucuxi
Member
From: Switzerland
Registered: 2020-03-08
Posts: 291

Re: [SOLVED] How do I debug my avahi/mdns setup?

First thing I would take care of

*** WARNING: Detected another IPv4 mDNS stack running on this host

Is systemd-resolved configured for mDNS?

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#3 2021-11-04 01:12:40

mwigzell
Member
Registered: 2016-01-29
Posts: 26

Re: [SOLVED] How do I debug my avahi/mdns setup?

I don't think so:

systemctl status systemd-resolved
○ systemd-resolved.service - Network Name Resolution
     Loaded: loaded (/usr/lib/systemd/system/systemd-resolved.service; disabled; vendor preset: enabled)
     Active: inactive (dead)
       Docs: man:systemd-resolved.service(8)
             man:org.freedesktop.resolve1(5)
             https://www.freedesktop.org/wiki/Software/systemd/writing-network-configuration-managers
             https://www.freedesktop.org/wiki/Software/systemd/writing-resolver-clients

How can I find that other mdns stack?
oK, its my browser Vivaldi:

lsof -i -P -n
COMMAND      PID USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
mpd         1152 mark   11u  IPv6   19829      0t0  TCP *:6600 (LISTEN)
mpd         1152 mark   18u  IPv6   36148      0t0  TCP 127.0.0.1:6600->127.0.0.1:41400 (ESTABLISHED)
mpd         1152 mark   19u  IPv6   36147      0t0  TCP 127.0.0.1:6600->127.0.0.1:41398 (ESTABLISHED)
vivaldi-b   1319 mark  188u  IPv4 1150887      0t0  UDP 224.0.0.251:5353 
vivaldi-b   1319 mark  235u  IPv4 1150888      0t0  UDP 224.0.0.251:5353 
cantata     1320 mark   23u  IPv4   33720      0t0  TCP 127.0.0.1:41398->127.0.0.1:6600 (ESTABLISHED)
cantata     1320 mark   31u  IPv4   33724      0t0  TCP 127.0.0.1:41400->127.0.0.1:6600 (ESTABLISHED)
panel-27-   1376 mark   10u  IPv4 1038687      0t0  TCP 127.0.0.1:41446->127.0.0.1:6600 (CLOSE_WAIT)
vivaldi-b   1549 mark   24u  IPv4 1522078      0t0  TCP 10.8.3.8:55722->151.101.41.140:443 (ESTABLISHED)
vivaldi-b   1549 mark   28u  IPv4 1522079      0t0  TCP 10.8.3.8:41518->192.0.0.69:443 (ESTABLISHED)
vivaldi-b   1549 mark   37u  IPv4 1505163      0t0  UDP 10.8.3.8:57419->142.250.217.106:443 
vivaldi-b   1549 mark   43u  IPv4 1522080      0t0  TCP 10.8.3.8:41520->192.0.0.69:443 (ESTABLISHED)
vivaldi-b   1549 mark   44u  IPv4 1511298      0t0  UDP 10.8.3.8:34636->142.250.217.74:443 
vivaldi-b   1549 mark   47u  IPv4 1522076      0t0  TCP 10.8.3.8:48550->116.203.93.142:443 (ESTABLISHED)
vivaldi-b   1549 mark   48u  IPv4 1525338      0t0  TCP 10.8.3.8:56780->104.198.23.205:443 (ESTABLISHED)
vivaldi-b   1549 mark   57u  IPv4 1506203      0t0  UDP 10.8.3.8:48283->74.125.195.189:443 
vivaldi-b   1549 mark   60u  IPv4 1511279      0t0  TCP 10.8.3.8:36812->54.172.122.55:443 (ESTABLISHED)
vivaldi-b   1549 mark   63u  IPv4  348774      0t0  UDP 224.0.0.251:5353 
vivaldi-b   1549 mark   69u  IPv4  348775      0t0  UDP 224.0.0.251:5353 
gvfsd-smb 139214 mark   10u  IPv4 1137594      0t0  TCP 127.0.0.1:57626->127.0.0.1:139 (ESTABLISHED)

ok, I turned off the Google DNS checkbox in Vivaldi/Settings/Privacy, (so no DNS leak) and I edited /etc/avahi/avahi-daemon.conf:

disallow-other-stacks=yes

After restarting linux, that warning is gone:

(base) mark@confucius:avahi$ systemctl status avahi-daemon
● avahi-daemon.service - Avahi mDNS/DNS-SD Stack
     Loaded: loaded (/usr/lib/systemd/system/avahi-daemon.service; enabled; vendor preset: disabled)
     Active: active (running) since Wed 2021-11-03 21:43:38 PDT; 7min ago
TriggeredBy: ● avahi-daemon.socket
   Main PID: 547 (avahi-daemon)
     Status: "avahi-daemon 0.8 starting up."
      Tasks: 2 (limit: 38369)
     Memory: 1.8M
        CPU: 21ms
     CGroup: /system.slice/avahi-daemon.service
             ├─547 "avahi-daemon: running [confucius.local]"
             └─562 "avahi-daemon: chroot helper"

Nov 03 21:43:38 confucius avahi-daemon[547]: Registering new address record for ::1 on lo.*.
Nov 03 21:43:38 confucius avahi-daemon[547]: Registering new address record for 127.0.0.1 on lo.IPv4.
Nov 03 21:43:38 confucius systemd[1]: Started Avahi mDNS/DNS-SD Stack.
Nov 03 21:43:39 confucius avahi-daemon[547]: Server startup complete. Host name is confucius.local. Local service cookie is 299382>
Nov 03 21:43:41 confucius avahi-daemon[547]: Registering new address record for fe80::a10d:70e5:6b18:9a6a on enp4s0.*.
Nov 03 21:43:45 confucius avahi-daemon[547]: Joining mDNS multicast group on interface enp4s0.IPv4 with address 192.168.86.43.
Nov 03 21:43:45 confucius avahi-daemon[547]: New relevant interface enp4s0.IPv4 for mDNS.
Nov 03 21:43:45 confucius avahi-daemon[547]: Registering new address record for 192.168.86.43 on enp4s0.IPv4.
Nov 03 21:43:48 confucius avahi-daemon[547]: Withdrawing address record for ::1 on lo.
Nov 03 21:43:48 confucius avahi-daemon[547]: Withdrawing address record for fe80::a10d:70e5:6b18:9a6a on enp4s0.

However, no joy with avahi:

(base) mark@confucius:avahi$ avahi-browse --all --ignore-local --resolve --terminate
(base) mark@confucius:avahi$

Last edited by mwigzell (2021-11-04 04:55:05)

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#4 2021-11-04 07:51:46

seth
Member
Registered: 2012-09-03
Posts: 51,270

Re: [SOLVED] How do I debug my avahi/mdns setup?

Do you disable the avahi cache? ("cache-entries-max=0", don't.)

Try to run "avahi-browse --all" (no resolution, no filtering and keep listening) - does that resolve /anything/?

You could try to use mdns4_minimal and also remove/comment the brother_printer from /etc/hosts

reg. the original problem: since you know the printer IP and it announces IPP, you could just add it in cups - mdns or not doesn't matter. In doubt nmap it to check that the port is open.

How to upload text · How to boot w/o GUI · Disable Windows Fast-Start! · Fix your xinitrc

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#5 2021-11-04 16:36:46

mwigzell
Member
Registered: 2016-01-29
Posts: 26

Re: [SOLVED] How do I debug my avahi/mdns setup?

I do not disable the cache. 

#cache-entries-max=4096

running "avahi-browse --all" doesn't resolve anythying:

(base) mark@confucius:avahi$ avahi-browse --all
+     lo IPv4 Music Player @ confucius[1183]                Music Player Daemon  local
+     lo IPv4 CONFUCIUS                                     Device Info          local
+     lo IPv4 CONFUCIUS                                     Microsoft Windows Network local

Yes, I tried mdns4_minimal, also I added the "brother_printer" AFTER the problem showed up, to make reading my printer easier in the tcpdumps. And yes, I have my printer working because I hard coded the IP in the cups printer. So I can print no problem. It is this lingering problem of not having the ".local" services even though, they were initially working last month. See my "nmap" dump above, the 5353 port is open.
I can't think of any other way to see into the avahi-browse, other than building it locally and running it in the debugger ....
The setup went from working to not working, and in the interim I did update packages cleanly. I was thinking, maybe "nordvpnd" re-writes the routing table or runs its own firewall or something. It does re-write the "/etc/resolv.conf" with its own DNS servers. The port is open, and when nordvpn is up, it has a small firewall. But when I stop nordvpn the firewall goes away. Originally avahi-browse was working with nordvpn up or down, and that has no impact on it now either.
Another thing worth mentioning: I have two Macs on my LAN, and they are able to discover the printer no problem. So its local to my ARCH box.

Last edited by mwigzell (2021-11-04 16:44:59)

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#6 2021-11-04 18:15:07

mwigzell
Member
Registered: 2016-01-29
Posts: 26

Re: [SOLVED] How do I debug my avahi/mdns setup?

Update: I must have fixed issue when I removed the Vivaldi IPv4 mDNS stack above. Because I had re-enabled firewalld (but had it stopped), when I restarted ARCH the firewall came up again. I noticed this just now, stopped the firewall and now avahi is working again!. User error. Thanks for your help. 

(base) mark@confucius:system$ avahi-browse -a
+ enp4s0 IPv4 Brother MFC-L2710DW series                    _uscan._tcp          local
+ enp4s0 IPv4 Brother MFC-L2710DW series                    _privet._tcp         local
+ enp4s0 IPv4 Brother MFC-L2710DW series                    _scanner._tcp        local
+ enp4s0 IPv4 Brother MFC-L2710DW series                    Internet Printer     local
+ enp4s0 IPv4 Brother MFC-L2710DW series                    UNIX Printer         local
+ enp4s0 IPv4 Brother MFC-L2710DW series                    PDL Printer          local
+ enp4s0 IPv4 dp-520202N9                                   SFTP File Transfer   local
+ enp4s0 IPv4 dp-520202N9                                   SSH Remote Terminal  local
+ enp4s0 IPv4 WDMyCloudEX2                                  _wd-2go._tcp         local
+ enp4s0 IPv4 Brother MFC-L2710DW series                    Web Site             local
+ enp4s0 IPv4 WDMyCloudEX2                                  Web Site             local
+ enp4s0 IPv4 WDMyCloudEX2_AFP_TimeMachineBackup            Apple TimeMachine    local
+ enp4s0 IPv4 WDMyCloudEX2                                  Apple File Sharing   local
+ enp4s0 IPv4 WDMyCloudEX2_AFP_TimeMachineBackup            Apple File Sharing   local
+ enp4s0 IPv4 dp-520202N9 [00:00:00:00:00:00]               Workstation          local
+ enp4s0 IPv4 WDMyCloudEX2-3 [00:90:a9:e3:13:3b]            Workstation          local
+ enp4s0 IPv4 WDMyCloudEX2                                  iTunes Audio Access  local
+ enp4s0 IPv4 WDMyCloudEX2                                  _rsp._tcp            local
+ enp4s0 IPv4 Roku Ultra                                    AirPlay Remote Video local
+ enp4s0 IPv4 CONFUCIUS                                     Microsoft Windows Network local
+     lo IPv4 CONFUCIUS                                     Microsoft Windows Network local
+ enp4s0 IPv4 CONFUCIUS                                     Device Info          local
+     lo IPv4 CONFUCIUS                                     Device Info          local
+ enp4s0 IPv4 Music Player @ confucius[1183]                Music Player Daemon  local
+     lo IPv4 Music Player @ confucius[1183]                Music Player Daemon  local
+ enp4s0 IPv4 Sonos-000E58B283E4                            _sonos._tcp          local
+ enp4s0 IPv4 Sonos-000E589977A0                            _sonos._tcp          local
+ enp4s0 IPv4 Sonos-000E58F016D8                            _sonos._tcp          local
+ enp4s0 IPv4 Sonos-000E58F0B350                            _sonos._tcp          local
+ enp4s0 IPv4 4de5187a-1def-5cde-9fd0-6b6558b8b95b          _spotify-connect._tcp local
+ enp4s0 IPv4 sonos000E583DF6CE                             _spotify-connect._tcp local
+ enp4s0 IPv4 Sonos-000E583DF6CE                            _sonos._tcp          local
+ enp4s0 IPv4 sonos000E58B283E4                             _spotify-connect._tcp local
+ enp4s0 IPv4 sonos000E582DF2E4                             _spotify-connect._tcp local
+ enp4s0 IPv4 Sonos-000E582DF2E4                            _sonos._tcp          local

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