Uptimerobot: TCP uptime only verifies the three-way TCP handshake
Posted by jpluimers on 2020/12/28
I like uptimerobot a lot (wrote about it earlier, and will write about it soon again), but there are two important things to keep in mind on how it does connection uptime verification:
- HTTP checks: [WayBack] Introducing “HTTP Method Selection” (HEAD/GET/POST/PUT/PATCH/DELETE) | Uptime Robot – Blog
- HTTP requests by default are HEAD for plain HTTP monitors or GET for HTTP keyword monitors, but in the advanced settings, you have options to choose other methods as well: HEAD/GET/POST/PUT/PATCH/DELETE are supported, which means the only unsupported methods (see Hypertext Transfer Protocol: Request Methods – Wikipedia) are TRACE/OPTIONS/CONNECT.
- TCP checks: [WayBack] New Feature – Monitoring Ports | Uptime Robot – Blog
TCP requests only perform the TCP connection three-way handshake (see Transmission Control Protocol: Connection establishment – Wikipedia and Handshaking: TCP three way handshake – Wikipedia).
- This means that for both stock supported TCP ports and custom TCP ports, no protocol specific steps are taken:
- Port 21 (File Transfer Protocol – Wikipedia) does not try to set active or passive
- Port 25 (Simple Mail Transfer Protocol – Wikipedia) does no HELO or EHLO
- Port 110 (Post Office Protocol – Wikipedia) does no APOP, USER or QUIT
- Port 143 (Internet Message Access Protocol – Wikipedia) does no
- The effect is that if for instance the POP3 service is behind an daemon like inetd – Wikipedia, and
inetresponds to TCP, but POP3 does not on the protocol, that uptimerobot still reports that POP3 works. - The exception above is already mentioned: the Hypertext Transfer Protocol – Wikipedia
- This means that for both stock supported TCP ports and custom TCP ports, no protocol specific steps are taken:
If you want to see a few specific TCP protocol tests in action, then check these:
- [WayBack] Online FTP tester
- [WayBack] Test an FTP Server – Wormly
- [Archive.is] Test Smtp
- [WayBack] Test your SSL POP3 Mail Server – Wormly
- [WayBack] Free SSL Web Server Tester – Wormly
- [WayBack] Web-Based Remote Ping Tool – Wormly
I did not find a good site to test IMAP servers in a simple way like the above sites. If anyone has one: please share it in a comment below.
I did find a post with public FTP servers (they are becoming rare): [WayBack] Is there a Public FTP server to test upload and download? – Stack Overflow
The Wiert Corner - irregular stream of stuff 
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