• avahidaemon causing slow DNS Resolution

    Interstellar

    By Interstellar

      • Minor

    Randomly hit by this today, nothing else of mine is suffering from this problem (Mac, RPIs, Windows machines and indeed a VM on the NAS itself!)

     

    Seems similar issues reported here: 

     

     

    During startup you can see I can ping bbc.co.uk at a regular 1 sec cadence, as is expected.

     

    However between 1650491180 and 1650491186 something happens to cause the ping DNS resolution to slow to a crawl.

      

    [1650491160.677062] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=2 ttl=57 time=7.19 ms
[1650491161.680240] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=3 ttl=57 time=7.59 ms
[1650491162.680644] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=4 ttl=57 time=7.59 ms
[1650491163.682572] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=5 ttl=57 time=7.72 ms
[1650491164.684427] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=6 ttl=57 time=7.59 ms
[1650491165.686395] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=7 ttl=57 time=7.63 ms
[1650491166.687953] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=8 ttl=57 time=7.66 ms
[1650491167.688993] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=9 ttl=57 time=7.81 ms
[1650491168.692176] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=10 ttl=57 time=7.97 ms
[1650491169.692828] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=11 ttl=57 time=7.70 ms
[1650491170.695271] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=12 ttl=57 time=7.46 ms
[1650491171.697118] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=13 ttl=57 time=7.77 ms
[1650491172.698616] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=14 ttl=57 time=7.86 ms
[1650491173.699806] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=15 ttl=57 time=7.86 ms
[1650491174.699658] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=16 ttl=57 time=7.54 ms
[1650491175.701393] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=17 ttl=57 time=7.55 ms
[1650491176.704215] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=18 ttl=57 time=7.83 ms
[1650491177.705895] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=19 ttl=57 time=7.73 ms
[1650491178.707608] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=20 ttl=57 time=7.95 ms
[1650491179.709268] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=21 ttl=57 time=7.81 ms
[1650491180.710587] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=22 ttl=57 time=7.58 ms
[1650491186.712848] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=23 ttl=57 time=7.68 ms
[1650491188.485948] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=24 ttl=57 time=7.81 ms
[1650491188.495136] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=25 ttl=57 time=7.68 ms
[1650491194.497036] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=26 ttl=57 time=7.68 ms
[1650491199.507572] 64 bytes from 2a04:4e42:200::81 (2a04:4e42:200::81): icmp_seq=27 ttl=57 time=7.85 ms

     

     

    If I decode the unix time, this command is shown in the log:

     

    Apr 20 22:46:21 NAS emhttpd: shcmd (18): /etc/rc.d/rc.avahidaemon start

     

    If I then run:

     

    /etc/rc.d/rc.avahidaemon stop

     

    The ping behaviour etc goes back to how it is supposed to be?

     

    What is mDNS doing and why is it causing ping name resolution to fall over?

     

    (This problem also prevented me from updating dockers, pulling apps, etc and happens in safe mode too).

     

    Edit: Happens on 6.9 and 6.10rc3.

     

    Go to reports Prereleases

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    bonienl
    Quote

    What is mDNS doing and why is it causing ping name resolution to fall over?

     

    Avahi is a system which facilitates service discovery on a local network via the mDNS/DNS-SD protocol suite. This enables you to plug your laptop or computer into a network and instantly be able to view other people who you can chat with, find printers to print to or find files being shared. Avahi is primarily targeted at Linux systems.

     

    Avahi interacts with DNS to do name resolution for local devices. In case this is not needed, e.g. no additional linux PCs are hot-plugged in your LAN network, you can disable the service by editing the file share.cfg in the /config folder on your USB device and set 

    shareAvahiEnabled="no"


    After saving the file, reboot the system to make the setting active.

    Note: this is not a true resolution of the problem you observed, but more a workaround which avoids the problem.

     

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    Interstellar

    Sorry totally forgot about this as the next day it suddenly started working with no changes by me other than booting it up again..!

     

    If it happens again I’ll run that command, thanks!

    Edited by Interstellar
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