This page measures the randomness of the DNS resolver’s source port and transaction ID. Sufficient randomness helps to prevent cache poisoning and reduces the ability of attackers to predict query parameters.
Select the number of samples (100–1000). When Run is selected, the browser initiates that many DNS lookups. The server records the source port and transaction ID for each query and displays ratings, histograms, and a chi-squared uniformity score (0–100).
Port and ID ratings (GREAT / GOOD / POOR) are based on the standard deviation of the observed values. A higher spread indicates better randomness. For the Port χ² and ID χ² statistics, lower values indicate a more uniform distribution. The page also reports 0x20 QNAME case support when the resolver varies letter case in queries.