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F5-303: BIG-IP platform configuration and traffic management

F5-303 · Work through your exam, one topic at a time.

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BIG-IP platform configuration and traffic management

Domain 2 tests object-level configuration: how virtual servers, profiles, pools, monitors, persistence and SNAT combine into working traffic management, and how the platform decides where a connection goes.

The object model and inheritance

  • Chain: node, pool member, pool, virtual server. Profiles supply protocol behaviour and inherit from the parent folder (/Common by default), so a setting you cannot find locally is probably inherited.
  • Monitors can attach at node, pool or member level; the most specific assignment wins. Interval, timeout and up/down counts determine detection time, not just health.
  • Availability (monitor-driven up/down) is separate from administrative state (enabled, disabled, forced offline). A disabled member receives no new connections even with a passing monitor.

Choosing a member

  • Methods include round robin, least connections, observed, predictive, ratio, dynamic ratio, fastest and least sessions. Persistence overrides the method until the persistence entry expires.
  • Priority Group Activation keeps traffic inside the highest-priority group only while that group has at least the configured minimum number of available members; below that threshold, the next group activates.

Worked example

A pool holds A and B in priority group 1 and C in group 2, with Priority Group Activation set to a minimum of two members. A's monitor fails. Reasoning: group 1 now has one available member, below the minimum, so group 2 activates and C starts receiving new connections. When A recovers, group 1 is back above the threshold and C stops receiving new traffic while existing connections continue. With a minimum of one, C would have stayed idle throughout.

Profiles and connection handling

  • Cookie persistence and HTTP iRule commands require an HTTP profile on the virtual server.
  • OneConnect reuses server-side connections, changing the server's view of concurrency and interacting with SNAT and keep-alives.
  • Client-ssl and server-ssl profiles are independent: certificates, ciphers and SNI belong to the client-side profile.

Traps that cost marks

  • Reading 'available, enabled' as healthy without checking the monitor.
  • Forgetting the default pool fallback when every member is down.
  • Enabling cookie persistence with no HTTP profile and expecting it to work.