Test a UDP endpoint before buying

5 datagrams answer the first question

Before payment, the endpoint tester checks whether the exact public destination socket admits a probe whose sender field equals 203.23.178.228. This check is free and needs no account.

The test sends real UDP datagrams. It does not simulate a firewall rule in the browser. A short-lived probe session creates a random nonce, sends five numbered datagrams from the same source IP used by the paid feed, and waits for the receiver to acknowledge those nonces through the tool's HTTPS reporting endpoint. The page updates as acknowledgements arrive.

A browser cannot listen on an arbitrary UDP port. The target machine therefore runs the displayed temporary receiver command or integrates the small acknowledgement format into an existing listener. UDP delivery and HTTPS reporting are separate paths. The UDP packet proves inbound reachability. The HTTPS acknowledgement lets the browser learn the result.

Method

Each probe begins with the same protocol family used for destination verification and includes a random session identifier plus a sequence from 1 through 5. The nonce is unguessable for the short session. The receiver checks it, records arrival time, and acknowledges the sequence over HTTPS.

The result uses four values:

sent = 5received = number of distinct acknowledged sequencesloss_percent = 100 * (sent - received) / sentspread_ms = last_udp_arrival_ms - first_udp_arrival_ms

Duplicate acknowledgements do not increase received. Acknowledgements with the wrong nonce or an expired session are ignored. The session expires after 600 seconds, matching the product's challenge lifetime.

For this test, the sender owns 203.23.178.228 throughout the probe. Traffic from an unrelated cloud address would not validate the production allowlist. Delivery targets the visitor's exact public IPv4 value and chosen UDP socket.

The tool validates the address before sending. It rejects private, loopback, link-local, multicast, broadcast, unspecified, and malformed targets. It caps requests per session and per destination. Those controls keep a free diagnostic from becoming a general packet source.

Worked example

Assume the intended receiver is public address 203.0.113.40 on UDP port 9000. The example address is documentation space, so a real test must use an address you control.

The user starts the temporary receiver on the target host, enters its real public IP and port in the page, then presses send. Using fixed sender 203.23.178.228, service transmits sequences 1 through 5. Its receiver sees sequences 1, 2, 4, and 5 and acknowledges them. Sequence 3 does not arrive before the deadline.

The page calculates:

sent = 5received = 4loss_percent = 100 * (5 - 4) / 5 = 20 percent

The result is partial reachability. It proves the source and destination tuple can pass at least some traffic. It also says the five-packet test was not clean. The next step is to inspect host firewall counters, cloud firewall rules, NAT state, and socket receive counters, then repeat.

If all five arrive across repeated tests, the page reports reachable. That is enough to answer whether packets can reach the listener now. It is not enough to establish production capacity.

Read failures by boundary

Zero acknowledgements has several possible causes. The UDP datagrams may not reach the host. The cloud security group may block them. A network firewall or NAT rule may point at another machine. The process may not be bound to the named port. The temporary receiver may receive UDP but fail to reach the HTTPS acknowledgement service.

The command prints local receipt before attempting acknowledgement. If it prints a valid nonce but the page remains waiting, inbound UDP worked and outbound HTTPS reporting failed. If it prints nothing, inspect packet capture and counters on the target.

Use a narrow capture filter:

source host 203.23.178.228 and UDP destination port 9000

When packets reach the interface but not the process, inspect the NIC-to-socket path: kernel firewall, binding, and receive queue. When the interface stays empty, inspect provider rules, routing, public-address mapping, and upstream filtering.

What success proves

Success establishes that the named UDP socket received at least one real 203.23.178.228 datagram during the active 600-second session and reported its nonce. Five of five gives a cleaner reachability signal than one packet because it catches an intermittent drop in a tiny sample.

Success also verifies the operator tested the exact port rather than a nearby TCP service. UDP and TCP firewall rules are different. A listening TCP command on port 9000 says nothing about UDP port 9000.

This pre-purchase test matches paid delivery: Frankfurt-origin raw UDP aimed at the precise socket the visitor registered. Checkout cannot make a receiver that fails all five probes ready.

Limitations

Five packets do not estimate loss at production confidence. One lost packet produces a coarse 20 percent result. Use a longer controlled sample and shred sequence analysis for packet-loss measurement.

The test does not reproduce sustained feed load. It does not exercise short bursts, kernel receive-buffer pressure, decoder throughput, or application queues. Passing the probe can coexist with heavy production loss.

The test does not prove the destination is safe to expose, that its firewall denies other sources, or that source IP filtering is cryptographic authentication. It does not test packet ordering or retransmission because raw UDP provides neither.

NAT mappings can expire, and a port opened by outbound test traffic may close later. Cloud rules can differ across instances or interfaces. Changing the public address triggers verification again under the product workflow.

The tool reports observed delivery, not why a packet failed. Its most valuable result is often a clean boundary: sender dispatched, interface saw nothing, or receiver saw UDP but acknowledgement failed. That evidence turns a vague activation problem into a specific network check.