fix: skip TTL update for OPT records

dns/util.go

@@ -96,6 +96,9 @@ func setMsgTTL(msg *D.Msg, ttl uint32) {
 	}
 
 	for _, extra := range msg.Extra {
+		if extra.Header().Rrtype == D.TypeOPT { // TTL section in OPT is the extended RCODE and flags (RFC 6891), not real TTL value
+			continue
+		}
 		extra.Header().Ttl = ttl
 	}
 }