Convergence timers
BGP today has a global convergence and propagation time of approx. 3 minutes as shown by recent research
Determining the optimal DNS RR expiration timeout is balancing between two opposite tradeoffs:
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- If the expiry timeout is low this will add latency during a session leading to poor responsiveness experience by the user because of multiple successive DNS requests
- if the expiration timeout is high this may reuse cached values with now sub-optimal path information or, if the link of the preferred IP has gone down in the meantime, to partial unreachability until the cached DNS RR expires
We recommend DNS RR expiry timeouts between 20 seconds and 2 hours