mustHaveExternalNetwork(t)
	testenv.SkipFlakyNet(t)

	if !supportsIPv4() || !*testIPv4 {
		t.Skip("IPv4 is required")
	}

	defer dnsWaitGroup.Wait()

	attempts := 0
	for i := 0; i < len(lookupCNAMETests); i++ {
		tt := lookupCNAMETests[i]
		cname, err := LookupCNAME(tt.name)
		if err != nil {
			testenv.SkipFlakyNet(t)
			if attempts < len(backoffDuration) {

func SkipFlaky(t testing.TB, issue int) {
	t.Helper()
	if !*flaky {
		t.Skipf("skipping known flaky test without the -flaky flag; see golang.org/issue/%d", issue)
	}
}

func SkipFlakyNet(t testing.TB) {
	t.Helper()
	if v, _ := strconv.ParseBool(os.Getenv("GO_BUILDER_FLAKY_NET")); v {
		t.Skip("skipping test on builder known to have frequent network failures")
	}
}