<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<meta name="Generator" content="Microsoft Word 15 (filtered medium)">
<style><!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Aptos;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0cm;
font-size:12.0pt;
font-family:"Aptos",sans-serif;
mso-ligatures:standardcontextual;
mso-fareast-language:EN-US;}
span.EmailStyle17
{mso-style-type:personal-compose;
font-family:"Aptos",sans-serif;
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;
mso-fareast-language:EN-US;}
@page WordSection1
{size:612.0pt 792.0pt;
margin:72.0pt 72.0pt 72.0pt 72.0pt;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
</head>
<body lang="EN-AU" link="#467886" vlink="#96607D" style="word-wrap:break-word">
<div class="WordSection1">
<p class="MsoNormal"><span lang="EN-US">Please help stop the mDNS flood.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">I have enabled MulticastDNS in one of my network files (see below). When I start the systemd-resolved service it consumes >90% CPU. Other machines on the network are being flooded by mDNS packets and their CPU also gets
loaded. Capturing a trace with tcpdump shows the server is sending a flood of mDNS packets.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">If I disable MulticastDNS in the network file or stop systemd-resolved service, the mDNS flood stops.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Here’s a small portion of tcpdump showing the flood from one server.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">$ tcpdump -i eno0 port 5353 and src srv<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">09:59:13.864876 IP srv.mdns > mdns.mcast.net.mdns: 0 [b2&3=0x400] [1au] TXT (QM)? PX3-1173-N1Q1V2K002 My PDU._snmp._udp.local. (114)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">09:59:13.865023 IP srv.mdns > mdns.mcast.net.mdns: 0 [b2&3=0x400] [1au] SRV (QM)? PX3-1173-N1Q1V2K002 My PDU._raritan_rpcs._tcp.local. (125)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">09:59:13.865208 IP srv.mdns > mdns.mcast.net.mdns: 0 [b2&3=0x400] [1au] TXT (QM)? PX3-1173-N1Q1V2K002 My PDU._raritan_rpcs._tcp.local. (132)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">09:59:13.891815 IP srv.mdns > mdns.mcast.net.mdns: 0 [b2&3=0x400] [1au] TXT (QM)? PX3-1173-N1Q1V2K002 My PDU._raritan_rpcs._tcp.local. (132)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">09:59:13.891973 IP srv.mdns > mdns.mcast.net.mdns: 0 [b2&3=0x400] [1au] SRV (QM)? PX3-1173-N1Q1V2K002 My PDU._raritan_rpcs._tcp.local. (125)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">09:59:13.892108 IP srv.mdns > mdns.mcast.net.mdns: 0 [b2&3=0x400] [1au] TXT (QM)? PX3-1173-N1Q1V2K002 My PDU._https._tcp.local. (115)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">09:59:13.892222 IP srv.mdns > mdns.mcast.net.mdns: 0 [b2&3=0x400] [1au] TXT (QM)? PX3-1173-N1Q1V2K002 My PDU._snmp._udp.local. (114)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Why is systemd-resolved issuing these queries?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">How do I configure it to stop the mDNS flood?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">$ networkctl cat 10-eno0.network<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"># /etc/systemd/network/10-eno0.network<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">[Match]<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">KernelCommandLine=!nfsroot<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Name=eno0<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">[DHCP]<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">ClientIdentifier=mac<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">RouteMetric=10<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">UseDomains=yes<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">UseHostname=yes<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">UseMTU=yes<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">[IPv6AcceptRA]<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">UseRedirect=no<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">[Link]<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">RequiredForOnline=no<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">[Network]<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">DHCP=yes<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">LinkLocalAddressing=yes<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">MulticastDNS=yes<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Thanks,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Matt.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
</div>
</body>
</html>