Jul 30 – 31, 2022
Sheraton Philadelphia Downtown
US/Eastern timezone

Round Trip Times Between Resolvers and a Root Server

Jul 30, 2022, 3:40 PM
Liberty D (Sheraton Philadelphia Downtown)

Liberty D

Sheraton Philadelphia Downtown

201 North 17th Street Philadelphia PA 19103 United States
Lightning Talk Main Session OARC 38 Day 1


Paul Hoffman (ICANN)


One of the stated goals of people asking for root server instances to be added near their resolvers is to get better round trip times. These requests are made without knowing any specific metric of what a good round trip time is, or knowing what round trip times typical resolvers are currently seeing. The research in this presentation focuses on the second question.

Many root server operators can easily determine typical round trip times by sampling the addresses in the traffic stream to their anycast instances and sending pings from the instances to the querying addresses. The ICANN Managed Root Server (commonly also known as L-root) is not able to do this due to contractual agreements that prevent originating traffic measurement queries from their instances. However, this restriction does not completely prevent such measurements because the servers collect IP TTL values for incoming queries.

This research shows how, using probing from RIPE Atlas systems, the IP TTL values seen can be converted to approximate round trip times and aggregated across instances. The research results estimate the median and 90th percentile measurements for round trip times for current resolvers.

Presentation delivery In-person at the workshop venue

Primary author

Paul Hoffman (ICANN)

Presentation materials