@aequitas first spotted and solved this bug in 6fcd182, 172.42.0. got replaced by 172.16.42., but 172.43.0. is still in use (and also outside of the 172.16.0.0/12 Private-Use as defined by RFC 1918 - Address Allocation for Private Internets - §3 Private Address Space / IANA IPv4 special registry ):

• Internet.nl/documentation/Docker-integration-tests.md

  Line 21 in c2162fd

  All IP addresses used in the isolated network are in private address ranges (`172.43.0.0/24`, `fd00:43:1::/64`) and all domain names use the `.test` domain. The internal `resolver` runs dnsmasq to provide routing of the internal domain and stub records for external services (eg: Cymru origin ASN query). The resolver configuration file is `docker/integration-tests/dnsmasq/entrypoint.sh`.

• Internet.nl/docker/test.env

  Lines 23 to 36 in c2162fd

  	IPV4_SUBNET_PUBLIC=172.43.0.0/16
  	IPV4_IP_PUBLIC=172.43.0.100
  	IPV4_WEBSERVER_IP_PUBLIC=172.43.0.100
  	IPV4_UNBOUND_IP_PUBLIC=172.43.0.101
  	IPV6_UNBOUND_IP_PUBLIC=fd00:43:1::101
  	# use fixed IPv4 addresses for internal networking to prevent resolving cache issues when recreating containers
  	IPV4_SUBNET_INTERNAL=192.168.43.0/24
  	IPV4_IP_MOCK_RESOLVER_PUBLIC=172.43.0.114
  	IPV6_IP_MOCK_RESOLVER_PUBLIC=fd00:43:1::114
  	IPV4_IP_TEST_TARGET_PUBLIC=172.43.0.51
  	IPV4_IP_TEST_TARGET_MAIL_PUBLIC=172.43.0.52

• Internet.nl/docker/batch-test.env

  Lines 24 to 37 in c2162fd

  	IPV4_SUBNET_PUBLIC=172.43.0.0/16
  	IPV4_IP_PUBLIC=172.43.0.100
  	IPV4_WEBSERVER_IP_PUBLIC=172.43.0.100
  	IPV4_UNBOUND_IP_PUBLIC=172.43.0.101
  	IPV6_UNBOUND_IP_PUBLIC=fd00:43:1::101
  	# use fixed IPv4 addresses for internal networking to prevent resolving cache issues when recreating containers
  	IPV4_SUBNET_INTERNAL=192.168.43.0/24
  	IPV4_IP_MOCK_RESOLVER_PUBLIC=172.43.0.114
  	IPV6_IP_MOCK_RESOLVER_PUBLIC=fd00:43:1::114
  	IPV4_IP_TEST_TARGET_PUBLIC=172.43.0.51
  	IPV4_IP_TEST_TARGET_MAIL_PUBLIC=172.43.0.52

• Internet.nl/docker/integration-tests/mock-resolver/test.zone

  Lines 5 to 65 in c2162fd

  	internet A 172.43.0.100
  	; IPV6_IP_PUBLIC
  	AAAA fd00:43:1::100
  	; all it's subdomains
  	nl.internet CNAME internet
  	en.internet CNAME internet
  	www.internet CNAME internet
  	; IPv6 only address
  	; IPV6_IP_PUBLIC
  	ipv6.internet AAAA fd00:43:1::100
  	; and it's subdomains
  	nl.ipv6.internet CNAME ipv6.internet
  	en.ipv6.internet CNAME ipv6.internet
  	www.ipv6.internet CNAME ipv6.internet
  	; connection test domain and subdomains
  	conn.internet CNAME internet
  	nl.conn.internet CNAME internet
  	en.conn.internet CNAME internet
  	www.conn.internet CNAME internet
  	; and the IPv6 only subdomains
  	conn.ipv6.internet CNAME ipv6.internet
  	conn.nl.ipv6.internet CNAME ipv6.internet
  	conn.en.ipv6.internet CNAME ipv6.internet
  	conn.www.ipv6.internet CNAME ipv6.internet
  	; nameserver setup for the connection test
  	test-ns-signed.internet NS ns.test-ns-signed.internet
  	; IPV4_UNBOUND_IP_PUBLIC
  	ns.test-ns-signed.internet A 172.43.0.101
  	; IPV6_UNBOUND_IP_PUBLIC
  	AAAA fd00:43:1::101
  	test-ns6-signed.internet NS ns.test-ns6-signed.internet
  	; IPV6_UNBOUND_IP_PUBLIC
  	ns.test-ns6-signed.internet AAAA fd00:43:1::101
  	platforminternet CNAME internet
  	; configure DNS for targets that are tested by the internet.test instance
  	; normal 100% website test target
  	; IPV4_IP_TEST_TARGET_PUBLIC
  	target A 172.43.0.51
  	; IPV6_IP_TEST_TARGET_PUBLIC
  	AAAA fd00:43:1::51
  	*.target CNAME target
  	; normal 100% email test target
  	*.mail-target MX 10 mx.mail-target.test.
  	; IPV4_IP_TEST_TARGET_MAIL_PUBLIC
  	mx.mail-target A 172.43.0.52
  	; IPV6_IP_TEST_TARGET_MAIL_PUBLIC
  	AAAA fd00:43:1::52
  	; unhappy flows
  	; badly configured IPv6 DNS servers
  	bad-ipv6-ns NS good-ns1.bad-ipv6-ns
  	NS bad-ns2.bad-ipv6-ns
  	NS bad-ns3.bad-ipv6-ns
  	; IPV4_IP_MOCK_RESOLVER_PUBLIC
  	good-ns1.bad-ipv6-ns A 172.43.0.114

• Internet.nl/docker/integration-tests/mock-resolver/bad-ipv6-ns.test.zone

  Lines 14 to 20 in c2162fd

  	good-ns1 A 172.43.0.114
  	good-ns1 AAAA fd00:43:1::114
  	bad-ns1 AAAA fd00:90::1
  	bad-ns2 AAAA fd00:90::2
  	; IPV4_IP_TEST_TARGET_PUBLIC
  	* A 172.43.0.51

BTW 172.43.0. also occurs in /integration_tests/batch/results.py which should be replaced with the new addresses.