DNS Caching Explained: Watch TTLs Count Down and NXDOMAIN Get Cached Too

Short summary

A Protocol Lab tutorial demonstrating DNS caching behavior by observing TTL countdowns for positive answers and negative caching of NXDOMAIN responses in a five-node containerlab topology. The lab shows how short-TTL records expire faster than long-TTL ones, and how SOA minimum controls negative-cache duration per RFC 2308. Uses BIND9 and netshoot containers with a 50–65 minute expected completion time.

• •Observe TTL countdown on cached positive DNS answers with different durations
• •Learn how NXDOMAIN responses carry SOA records and get negatively cached
• •Five-node topology with BIND9 resolver demonstrates real caching behavior

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