Recently I run into trouble using F5 load balancer; it was configured with standard TCP profile, and provided great performance within a data center. However, transfers crossing WAN boundaries had their throughput severely limited.
I don't normally deal with network devices, so it was a surprise for me when I found that the load balancer with TCP profile is in fact a proxy. The TCP profile limits send buffer size to 64 KB, and therefore limits throughput to 64KB / RTT, in our case 640KB/s.
After raising the send buffer size to 1MB we were able to get 10MB/s transfers, which were acceptable for our uses. Fortunately the F5 device had sufficient memory to support that buffer size.
Only later I found that F5 also supports fastL4 mode, in which case it does not act as a proxy, but rather as a regular router. In that mode the send buffer is controlled by the server directly. This reduces the memory requirements, allowing F5 to serve more connections, and shifts the responsibility for throughput to the application.
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