[Dnsmasq-discuss] DNSMasq with high Send/Receive buffers

[Simon Kelley]

We've been here before.

https://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2022q2/016324.html

Simon.


On 24/08/2022 23:42, Felipe Polanco wrote:
> Hello,
> 
> We are using dnsmasq as DNS server for our public VPN server and today 
> we found a rare issue where DNSMasq filled the entire send buffer of its 
> UDP socket.
> 
> dnsmasq.log
> 
> Aug 24 15:52:12 dnsmasq[5363]: failed to send packet: Resource 
> temporarily unavailable
> Aug 24 15:52:12 dnsmasq[5363]: cached www.google.com 
> <http://www.google.com/> is 216.58.223.196
> Aug 24 15:52:12 dnsmasq[5363]: query[A] www.google.com 
> <http://www.google.com/> from 105.112.28.230
> Aug 24 15:52:12 dnsmasq[5363]: failed to send packet: Resource 
> temporarily unavailable
> 
> # netstat -tulpana
> Active Internet connections (servers and established)
> Proto Recv-Q Send-Q Local Address           Foreign Address         
> State       PID/Program name
> tcp        0      0 0.0.0.0:111 <http://0.0.0.0:111/>             
> 0.0.0.0:*               LISTEN      1/systemd
> tcp        0      0 0.0.0.0:53 <http://0.0.0.0:53/>             
>   0.0.0.0:*               LISTEN      5363/dnsmasq
> tcp        0      0 0.0.0.0:22 <http://0.0.0.0:22/>             
>   0.0.0.0:*               LISTEN      3977/sshd
> <redacted>
> tcp6       0      0 :::111                  :::*                   
>   LISTEN      1/systemd
> tcp6       0      0 :::53                   :::*                   
>   LISTEN      5363/dnsmasq
> tcp6       0      0 :::22                   :::*                   
>   LISTEN      3977/sshd
> udp 14976 213504 0.0.0.0:53 <http://0.0.0.0:53/>              0.0.0.0:* 
>                            5363/dnsmasq
> 
> Low CPU usage, RAM is ok and disk is 38% used.
> 
> DNS resolution became very slow and we saw using tcpdump that maybe 1 
> out of 20 requests were answered.
> 
> nslookup to 8.8.8.8 works fine.
> 
> We restarted dnsmasq service and the issue went away immediately and the 
> Qs were back to 0 as expected.
> 
> I understand these Qs may fill up if there is no acknowledgment from the 
> peer while using TCP sockets but these are UDP and don't require ACK.
> 
> What could be the cause of this?
> 
> Thanks,
> 
> _______________________________________________
> Dnsmasq-discuss mailing list
> Dnsmasq-discuss at lists.thekelleys.org.uk
> https://lists.thekelleys.org.uk/cgi-bin/mailman/listinfo/dnsmasq-discuss