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Comprehensive and Detailed Explanation From BIG-IP Administration Support and Troubleshooting documents:When troubleshooting intermittent connection resets on a "busy" Virtual Server, the administrator must examine the configured thresholds62. A "Connection Limit" is a hard cap on the number of concurrent connections a Virtual Server or pool member can handle63. If this limit is set too low, the BIG-IP will reset any new connection attempts once the threshold is reached64. The key indicator in this scenario is that the problem only affects "some users" and happens when the server is "busy," suggesting that the system is hitting a capacity ceiling rather than suffering from a persistent configuration error65. Unlike a missing SSL profile, which would likely cause all connections to fail, or a "Connection Rate Limit," which throttles how fast connections arrive, a "Connection Limit" focuses on the total volume66. Identifying this as the cause requires reviewing the Virtual Server's statistics to see if the "Current Connections" count is consistently peaking at the configured limit value.

Uneven load balancing on a BIG-IP system typically occurs when traffic is not distributed evenly across all available pool members. One common reason is thatmonitors have marked down multiple pool members (Option B). When health monitors fail for specific pool members, BIG-IP automatically removes those members from load-balancing decisions. As a result, traffic is sent only to the remaining healthy member, creating the appearance that load balancing is not functioning correctly. This behavior is expected and aligns with BIG-IP’s design to ensure traffic is sent only to healthy resources.

Another frequent cause isthe presence of a persistence profile on the pool or virtual server (Option C). Persistence (such as source address or cookie persistence) forces subsequent client connections to be sent to the same pool member for session continuity. While persistence is critical for certain applications, it can override the load-balancing algorithm and cause most or all traffic to be directed to a single pool member, especially during low traffic volumes or testing scenarios.

The other options are incorrect because avirtual server marked down (Option A)would not pass traffic at all, andall pool members marked down (Option D)would result in no connections rather than uneven distribution. This analysis follows standard BIG-IP troubleshooting methodology using pool status, monitor results, and persistence configuration review.

This scenario describes a classic network performance issue known as the "Mega-Proxy" problem. When an organization routes all employee traffic through a single proxy server, the BIG-IP sees thousands of unique users as having the exact same source IP address. If the administrator has configured "Source Address Affinity" persistence, the BIG-IP will correctly follow the rule but incorrectly route all users to the same single backend pool member. This creates a severe load imbalance where one server is overwhelmed while others remain idle, leading to poor application response times. To resolve this, the administrator must change the persistence profile to "HTTP Cookie". Cookie-based persistence allows the BIG-IP to place a unique identifier in each user's browser, allowing the system to distinguish between individual sessions even if they share the same source IP. This fix ensures that traffic is distributed evenly across the pool members, restoring4 the expect5ed load balancing functionality and resolving the slow performance reported by users behind the corporate proxy.