How does the DNA's Active Latency Detection (ALD) work?
The Agent sends pings in groups of three. The pings are not actually ICMP ping requests, but TCP connection setup requests sent to a closed port, port 2408 by default. The expectation is that there is no listener on this socket at the remote server. This will force a connection refusal (an immediate TCP RST) for each ping, providing the DNA console with an accurate round trip measurement to each machine. Connection setup requests are used due to the higher service priority given them by a router, reducing congestion effects and resulting in the fastest possible round trip time. This translates into the most accurate latency measurement during capture. The term ping will continue to be used for convenience in this document.
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