[systemd-devel] systemd-resolved floods the network with mDNS packets

[Muggeridge, Matt]

Please help stop the mDNS flood.

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.

If I disable MulticastDNS in the network file or stop systemd-resolved service, the mDNS flood stops.

Here's a small portion of tcpdump showing the flood from one server.

$ tcpdump -i eno0 port 5353 and src srv
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)
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)
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)
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)
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)
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)
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)

Why is systemd-resolved issuing these queries?
How do I configure it to stop the mDNS flood?

$ networkctl cat 10-eno0.network
# /etc/systemd/network/10-eno0.network
[Match]
KernelCommandLine=!nfsroot
Name=eno0

[DHCP]
ClientIdentifier=mac
RouteMetric=10
UseDomains=yes
UseHostname=yes
UseMTU=yes

[IPv6AcceptRA]
UseRedirect=no

[Link]
RequiredForOnline=no

[Network]
DHCP=yes
LinkLocalAddressing=yes
MulticastDNS=yes

Thanks,
Matt.

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