Postfix behind Iptables masquerade (NAT)

I've been working on a mail server behind iptables masquerade for some days, and it just didn't work, but I found the solution, it may help you.

If you use SMTP server behind NAT, and you get the following errors:

• mail postfix/smtp[7854]: warning: host gmail-smtp-in.l.google.com[173.194.70.26]:25 greeted me with my own hostname mail.example.com
• mail for gmail.com loops back to myself

you should check your iptables configuration. A proper port-forward config:

iptables -A INPUT -p tcp -s 0/0 --sport 1024:65535 -d PUBLICIP --dport 25 -m state --state NEW,ESTABLISHED -j ACCEPT iptables -t nat -A PREROUTING -p tcp --dport 25 -i eth0 -j DNAT --to MAILSERVERPRIVATEIP:25

(Only forward packets from port 25 to your mail server's private IP port 25, if it comes from the outside.)

You can test it on your mail server by telnetting to a foreign smtp server for example:

telnet smtp.gmail.com 25

It should show:

Trying 173.194.70.108...
Connected to gmail-smtp-msa.l.google.com.
Escape character is '^]'.
220 mx.google.com ESMTP r54sm45040303eev.8 - gsmtp

If you see


220- mail.yourdomain.com gsmtp

you config is not good yet.

Cisco router Telnet Debug

On most of Cisco routers, debug informations via telnet is not enabled, so you will not see any debug information when connected via telnet.

To enable it, you need to enable virtual terminal first:
Router# terminal monitor

Next, you have to enable debugging on virtual monitor:

In privileged mode:
Router# undebug all

In configuration mode:

Router(config)# logging monitor debugging

Router(config)# logging on

To disable it:

In privileged mode:
Router# undebug all
Router# terminal no monitor

In configuration mode:

Router(config)# no logging monitor

Counter Strike: GO Classic Competitive ,MapGroup not found'

How to solve: ,,Mapgroup not found" error in CS:GO Classic Competitive:

1.
cd steam/csgo/csgo
nano gamemodes_server.txt

2.
You should find a commented line, starting with a 2:
2//some comment

3.
Delete 2 before the commetn:
//some comment

4.
Restart server

Now it should work, it's a bug, valve somehow left a ,,2" before the line, and because of that, the server thinks, that its the end-of-file, so the map groups are not loaded.

Windows Server 2008 R2 RDP Port Change

You need to do 3 steps to enable and change RDP Port in Windows Server 2008, 2008R2, 2012. You need to do this, if you have more servers at the same IP address, behind a router.

1st step: Enable RDP in System settings. You can go there by right clicking on Computer -> Propreties. Choose Advanced System Settings from the left side menu.

2nd Step: Change RDP Port: Open the registry editor (regedit: open cmd -> regedit.exe). Select HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\TerminalServer\WinStations\RDP-Tcp\PortNumber . Change to decimal mode, and change the port number, then click ok.

3rd Step: Enable the new Port in the Firewall settings. Open Server Manager, Select Firewall Settings in the left menu, right click on Inbound Rouls -> New. Choose TCP, set Port number, and name it.

Thats all. After this you should restart your server, then everything should work fine. Default port for RDP is 3389 (TCP). Enjoy.