DNS Split-Brain Lab: When Internal and External Users See Different Worlds

Some users reach the new service, some hit the old one, and internal staff see a third answer through VPN. Participants debug resolver caches, split-horizon DNS, stale records, TTL assumptions, CNAME chains, and region-specific responses.

The session builds a repeatable diagnostic pattern: compare resolvers, check authoritative answers, map network context, document expected records, and decide how to roll changes without leaving half the audience behind.