weave: Weave-NPC keeps logging about a blocked UDP connection from 0.0.0.0:68 to 255.255.255.255:67

What happened?

All weave-npc containers keep logging about a blocked UDP connection and they do so in very rapid succession:

WARN: 2019/07/05 11:12:25.102451 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102461 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102479 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102488 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102516 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102540 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102549 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102560 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102575 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102585 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102594 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102603 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102612 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102624 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102640 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102656 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102668 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102683 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102693 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102723 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102746 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102793 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102806 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102816 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102831 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102846 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102858 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102883 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102893 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102907 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102924 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102934 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.102952 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.494401 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.494433 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.494444 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.494454 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.494462 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.
WARN: 2019/07/05 11:12:25.494477 UDP connection from 0.0.0.0:68 to 255.255.255.255:67 blocked by Weave NPC.

How to reproduce it?

Unfortunately I do not know at this point.

Anything else we need to know?

This is a multi-AZ K8S cluster running Kubernetes 1.13.7 and Weave 2.5.2 Kubernetes is setup using kubeadm and the cluster currently runs in iptables mode (no IPVS yet).

Versions:

$ weave version 2.5.2

$ docker version

Client:
 Version:           18.06.3-ce
 API version:       1.38
 Go version:        go1.10.8
 Git commit:        d7080c1
 Built:             Tue Feb 19 23:07:53 2019
 OS/Arch:           linux/amd64
 Experimental:      false

Server:
 Engine:
  Version:          18.06.3-ce
  API version:      1.38 (minimum version 1.12)
  Go version:       go1.10.8
  Git commit:       d7080c1
  Built:            Tue Feb 19 23:07:53 2019
  OS/Arch:          linux/amd64
  Experimental:     false

$ uname -a Linux ip-10-1-1-1 4.19.43-coreos-r1 #1 SMP Tue Jun 11 07:24:09 -00 2019 x86_64 Intel(R) Xeon(R) Platinum 8175M CPU @ 2.50GHz GenuineIntel GNU/Linux

$ kubectl version

Client Version: version.Info{Major:"1", Minor:"15", GitVersion:"v1.15.0", GitCommit:"e8462b5b5dc2584fdcd18e6bcfe9f1e4d970a529", GitTreeState:"clean", BuildDate:"2019-06-19T16:40:16Z", GoVersion:"go1.12.5", Compiler:"gc", Platform:"linux/amd64"}
Server Version: version.Info{Major:"1", Minor:"13", GitVersion:"v1.13.7", GitCommit:"4683545293d792934a7a7e12f2cc47d20b2dd01b", GitTreeState:"clean", BuildDate:"2019-06-06T01:39:30Z", GoVersion:"go1.11.5", Compiler:"gc", Platform:"linux/amd64"}