Network & Infrastructure / IPv6, TCP & Transport Engineering
TCP RTT measurements and misleading capture timing
A packet capture suggests the server takes hundreds of milliseconds to respond, while endpoint telemetry reports low network RTT. Capture location, batching and application delay may explain the discrepancy.
Environment and inputs: Dual-stack routed networks and transport endpoints; validate the complete path and the active operating-system version. Diagnostic/design example; not tested on production equipment.
Collect the evidence
Record capture points, clock synchronization, NIC offloads and whether the measurement spans network acknowledgment or application processing. Compare local acknowledgment timing with end-to-end transaction timing.
Explain the result
Network RTT, server processing and user-visible response time are different intervals. Packet timestamps from unsynchronized hosts cannot be directly subtracted as if they shared one clock.
Plan the fix
Define the latency component being investigated and choose a measurement method appropriate to it. Use synchronized observations or same-point request/response measurements with documented limitations.
Check the result and rollback
Validate conclusions against an independent endpoint or synthetic transaction measure. Revert timing-based attribution if uncertainty exceeds the delay being blamed on a network segment.