fix: lowercase DNS extra record names

CHANGELOG.md

@@ -51,6 +51,14 @@ keys remain all-access.
 
 - `headscale users rename` now sends the identifier of the matched user instead of the raw `--identifier` flag value, so renaming by name works again [#3442](https://github.com/juanfont/headscale/pull/3442)
 
+## 0.29.4 (202x-xx-xx)
+
+**Minimum supported Tailscale client version: v1.80.0**
+
+### Changes
+
+- Lowercase DNS extra record names so mixed-case records resolve [#3366](https://github.com/juanfont/headscale/pull/3366)
+
 ## 0.29.3 (2026-07-29)
 
 **Minimum supported Tailscale client version: v1.80.0**

hscontrol/types/config.go

@@ -993,7 +993,7 @@ func dnsToTailcfgDNS(dns DNSConfig) *tailcfg.DNSConfig {
 
 	cfg.Proxied = dns.MagicDNS
 
-	cfg.ExtraRecords = dns.ExtraRecords
+	cfg.ExtraRecords = lowercaseRecordNames(dns.ExtraRecords)
 	if dns.OverrideLocalDNS {
 		cfg.Resolvers = dns.globalResolvers()
 	} else {
@@ -1475,6 +1475,22 @@ func (c *Config) SetExtraRecords(records []tailcfg.DNSRecord) {
 	defer tailcfgDNSMu.Unlock()
 
 	if c.TailcfgDNSConfig != nil {
-		c.TailcfgDNSConfig.ExtraRecords = records
+		c.TailcfgDNSConfig.ExtraRecords = lowercaseRecordNames(records)
 	}
 }
+
+// lowercaseRecordNames normalizes DNS record names to lowercase, as DNS names
+// are case-insensitive and clients match extra records by exact name.
+func lowercaseRecordNames(records []tailcfg.DNSRecord) []tailcfg.DNSRecord {
+	if len(records) == 0 {
+		return records
+	}
+
+	normalized := make([]tailcfg.DNSRecord, len(records))
+	for i, record := range records {
+		record.Name = strings.ToLower(record.Name)
+		normalized[i] = record
+	}
+
+	return normalized
+}

hscontrol/types/config_test.go

@@ -741,3 +741,32 @@ func TestTrustedProxies(t *testing.T) {
 		})
 	}
 }
+
+// DNS names are case-insensitive, but MagicDNS resolution in clients matches
+// extra records by exact name, so mixed-case record names never resolve.
+func TestExtraRecordsAreLowercased(t *testing.T) {
+	mixed := []tailcfg.DNSRecord{
+		{Name: "Printer.fritz.box", Type: "A", Value: "192.168.1.2"},
+		{Name: "NAS.FRITZ.BOX", Type: "A", Value: "192.168.1.3"},
+	}
+	want := []tailcfg.DNSRecord{
+		{Name: "printer.fritz.box", Type: "A", Value: "192.168.1.2"},
+		{Name: "nas.fritz.box", Type: "A", Value: "192.168.1.3"},
+	}
+
+	tcfg := dnsToTailcfgDNS(DNSConfig{
+		MagicDNS:     true,
+		BaseDomain:   "example.com",
+		ExtraRecords: mixed,
+	})
+	if diff := cmp.Diff(want, tcfg.ExtraRecords); diff != "" {
+		t.Errorf("dnsToTailcfgDNS extra records mismatch (-want +got):\n%s", diff)
+	}
+
+	cfg := &Config{TailcfgDNSConfig: &tailcfg.DNSConfig{}}
+	cfg.SetExtraRecords(mixed)
+
+	if diff := cmp.Diff(want, cfg.TailcfgDNSConfig.ExtraRecords); diff != "" {
+		t.Errorf("SetExtraRecords mismatch (-want +got):\n%s", diff)
+	}
+}