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Intermittent DCC, behind NAT? #263960 15/10/18 10:52 AM
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Shamrock Offline OP
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Sometimes DCC will work, but most of the time not. There doesn't appear to be any pattern to it. Even running with no router, firewall or AV it's the same. It can be working when I go to bed and not when I get up.

I think I might be behind a NAT firewall being run by my ISP, which I have no control over. My hostname in mIRC starts with natgw-

I've read through all the help files online and tried everything the suggest but nothing seems to make any it better.

I get the error: send incomplete (connection failed) when it fails. Is there any way I can get around this using a VPN or something?

Re: Intermittent DCC, behind NAT? [Re: Shamrock] #263962 15/10/18 11:37 AM
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Raccoon Offline
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You say "Even running with no router." In 2018, this is mostly not possible anymore... you are probably using a router and don't know it, or at least some sort of modem-hybrid equipment that performs some rudimentary network address translation.

One thing that crops up is a change in DCC behavior depending on whether you are connected to an IRC server via SSL or not SSL. When you are not connected via SSL, your equipment may attempt to intercept CTCP DCC packets and perform translation on them, open ports for you, etc. Sometimes it works, often times it breaks things. When you are connected to an IRC server via SSL, your NAT can no longer inspect and augment these same packets, and so it either works suddenly, or it stops working suddenly, whichever boat you happen to be in.

If you have mIRC set to choose a random port from a range of ports, try changing this to just one port, for testing purposes. It may be that some of your ports are forwarding but others are not. Range mismatch? Try selecting big numbers for port values, between 10000 and 64999, so there is less likely a conflict between mIRC and other software.

You should also make sure you use the mirc command /localinfo -u, so that mIRC knows what your public IP address is, and not just your local interface IP. The value of $ip should be your public IP address.

Type: //echo -a $ip
Visit https://www.google.com/search?q=my+ip+address

These should match.

Last edited by Raccoon; 15/10/18 01:35 PM. Reason: Sorry: SSL not SSH.

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Re: Intermittent DCC, behind NAT? [Re: Raccoon] #263964 15/10/18 12:53 PM
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Thanks for your reply Raccoon.

I don't have a router but my internet comes from a dish antenna on the roof, which will most likely have a built in router controlled by the ISP. The old one was made by Mikrotik, (I think they call them routerbords), I forget the brand of the latest one. I believe the system they use is called Wimax - Signal comes from an antenna about 15 miles away.

My external IP address is displaying correctly in mirc. I tried your port suggestions but unfortunately it made no difference.

When DCC works it doesn't work for everyone, some sends will succeed and others fail. It's not even the same people it works or fails for, so I doubt it's SSH.

Re: Intermittent DCC, behind NAT? [Re: Raccoon] #263970 16/10/18 09:28 AM
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Originally Posted By: Raccoon

If you have mIRC set to choose a random port from a range of ports, try changing this to just one port, for testing purposes. It may be that some of your ports are forwarding but others are not. Range mismatch? Try selecting big numbers for port values, between 10000 and 64999, so there is less likely a conflict between mIRC and other software.


I ran a scan on my ports and found one in the eight thousands that's open. I set mirc to use this port by setting it as the first and last port. I ran the server overnight to test it and it succeeded 4 out of 34 times.

Any idea why setting it to an open port made no difference?

Re: Intermittent DCC, behind NAT? [Re: Shamrock] #263979 16/10/18 07:38 PM
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Raccoon Offline
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I don't know. But I do know that you'll have a tough time at scanning your own ports, from the same location, in a meaningful way. What matters are outside scans from a remote terminal going into your home computer network. There are windows programs for opening ports and scanning ports, or you can write mIRC scripts that will do this too with /socklisten and /sockopen. This way you can get positive feedback on whether you can access a port consistently from the same remote location over multiple attempts over time. But you'll still need access to a computer away from home to conduct the scans.

When you have DCC ports reduced to a single port, only one transfer can take place at a time.


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