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TCP Handshake Test: Measure Connection Establishment Time
Every TCP connection begins with a three-way handshake: SYN, SYN-ACK, and ACK. This handshake adds overhead to every new connection. Our TCP handshake test measures the time each phase takes, helping diagnose server overload, network issues, and TLS overhead separately from data transfer time.
Launch in Mission ControlWhat It Measures
This tool measures the time for each phase of TCP connection establishment: SYN sent to SYN-ACK received (network round-trip time), and ACK sent to connection ready. For HTTPS endpoints, it measures TLS handshake time separately to break down connection overhead precisely.
How It Works
- Opens a raw TCP connection to the target host and port
- Records the exact timestamp of SYN, SYN-ACK, and ACK stages
- For HTTPS hosts, measures TLS ClientHello to ServerFinished timing
- Reports per-stage timing and totals with millisecond precision
Why It Matters
TCP handshake time is the minimum latency floor for any connection. Slow handshakes indicate either high network latency (physical distance), server overload (SYN queue backlog), or poor TLS configuration (redundant certificate validation). Identifying which phase is slow pinpoints the fix needed.
Understanding Your Results
TCP SYN to SYN-ACK should closely match your ping latency to the server. Total TCP handshake (without TLS) should complete in under 100ms for regional servers. TLS handshake adds 20 to 60ms typically. TLS 1.3 requires only one round trip for the handshake vs two for TLS 1.2, saving 20 to 60ms per new connection.
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Run TCP Handshake Test Now →Frequently Asked Questions
What is the TCP three-way handshake?
The TCP three-way handshake establishes a reliable connection between two hosts. The client sends SYN (synchronize), the server responds with SYN-ACK (synchronize-acknowledge), and the client sends ACK (acknowledge). This process must complete before any application data can be exchanged, adding one round-trip time of overhead to every new connection.
How does TLS add to TCP handshake time?
TLS adds its own negotiation on top of the TCP handshake. TLS 1.2 requires two additional round trips. TLS 1.3 reduces this to one round trip with 0-RTT session resumption available for reconnections. Moving from TLS 1.2 to 1.3 can save one full RTT on every new connection.
What is TCP Fast Open and does it help?
TCP Fast Open (TFO) allows application data to be sent during the SYN phase of the handshake for reconnecting clients, eliminating one round-trip delay on subsequent connections. It requires support from both client and server. Linux, macOS, and modern web servers support TFO, though some firewalls block SYN data.
What does a slow SYN-ACK indicate?
A slow SYN-ACK response (significantly higher than your baseline ping) indicates either server-side SYN queue saturation (the server is receiving more connection attempts than it can process, which can indicate a SYN flood attack or severe overload) or routing issues between you and the server.
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