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I have the dumbest problem that has me perplexed.

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SRV1 is the FTP server I'm trying to connect too... from inside my work network (CPU1) SRV2 is ftp.secureftp-test.com (random ftp server that I found, just to verify my computer can FTP out). CPU1 is a couple computers inside my work network. CPU2 is a computer outside of my work network.

I can connect to SRV1&2 from outside the network (CPU2). I know that the servers, users and passwords work on both servers from CPU2. I can connect to SRV2 (ftp.test) from inside my work network (multiple computers, multiple public IPs), but I can't connect to SRV1 (ISP hosted ftp server).

Firewall shouldn't be an issue, I can FTP out to SRV2 (as well as other servers). DNS isn't an issue (everything resolves correctly: I can view website on the same server).

Where can I go to troubleshoot this further? It's not a huge issue (workarounds already in place), but I just can't stand an unanswered riddle.

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And you're sure that your ISP isn't blocking FTP requests that don't originate from their own customers' IP's? –  Ian Atkin Nov 29 '12 at 18:46
    
@IanAtkin They have our public IP's added their input rules. SRV1 wouldn't accept CPU2 otherwise. Forgot to mention that. –  WernerCD Nov 29 '12 at 21:16
    
Please report what happens when doing telnet ftp.srv1.com 21. You should get a classic FTP header like 220---------- Welcome to Pure-FTPd [Srv1] [TLS] ----------. –  Sopalajo de Arrierez Apr 21 at 21:14
    
Please report what happens when scanning port 21TCP to SRV1 from online scanner sites, like this one: t1shopper.com/tools/port-scan –  Sopalajo de Arrierez Apr 21 at 21:15
    
This is longer advice, but could be useful too: if allowed, install nMap (installation of nMap is not agressive for operating systems): nmap.org . Then do nmap ftp.srv1.com -p 21 for FTP port scanning to your FTP SRV1, and later nmap ftp.srv1.com to get a complete TCP port scanning. Paste the results in your initial post. –  Sopalajo de Arrierez Apr 21 at 21:18

1 Answer 1

I would try the next:

1 - ping from cpu1 to srv1

2 - ssh from cpu1 to srv1

If you can ping and establish a ssh session then either srv1 is not answering the FTP request from cpu1 (ISP firewall block) or could be that the ip address/port that cpu1 is using to ftp srv1 is not correct. It could be that cpu1 is using a public IP address that has not been added to ISP firewall rules, it is worth to checking.

I hope you can find out.

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