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Charles Green
Asked: 2014-11-15 00:12:18 +0800 CST

AWS EC2 Ubuntu 14.04 Instance smtp port forwarding from 25 to 2025

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I am trying to step up port forwarding from port 25 to port 2025 on the same AWS EC2 Ubuntu 14.04 instance using iptables. I am using port 2025 to receive income emails using Alfresco.

The first step I took was to open port 25 for INBOUND traffic in the Security Group using the AWS Console. Next I followed the following steps using a new EC2 Ubuntu instance. My understanding is that the first command allows inbound traffic to port 25. The second command then forwards the traffic from port 25 to port 2025 and then the last step saves (but does not persist the settings).

sudo iptables -A INPUT -p tcp --dport 25 -j ACCEPT
sudo iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 25 -j REDIRECT --to-port 2025
sudo iptables-save

I've confirmed that Alfresco is listening on port 2025 and the iptable settings using the following commands: 

bitnami@ip-172-30-0-000:~$ netstat -an | grep 25

tcp6       0      0 :::2025                 :::*                    LISTEN   


bitnami@ip-172-30-0-000:~$ sudo iptables -t nat -L -n -v
Chain PREROUTING (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target     prot opt in     out     source    destination         
0     0 REDIRECT   tcp  --  eth0   *       0.0.0.0/0    0.0.0.0/0    tcp dpt:25 redir ports 2025

Chain INPUT (policy ACCEPT 0 packets, 0 bytes) 
pkts bytes target     prot opt in     out     source    destination         

Chain OUTPUT (policy ACCEPT 5 packets, 431 bytes)
pkts bytes target     prot opt in     out     source    destination         

Chain POSTROUTING (policy ACCEPT 5 packets, 431 bytes)
pkts bytes target     prot opt in     out     source    destination

When testing the connection with telnet I would expect something like the following however now the connection simply times out.

Expecting: 

Trying 54.85.10.9...
Connected to 54.163.62.000.
Escape character is '^]'.
220 simplycubedholdings.com ESMTP SubEthaSMTP 3.1.6
421 Timeout waiting for data from client.

Actual: 

telnet 54.163.62.000 25
Trying 54.163.62.000...
telnet: connect to address 54.163.62.000: Operation timed out
telnet: Unable to connect to remote host

Any help or direction would be greatly appreciated.

Many thanks,

Charles

iptables

1 Answers

  1. Many thanks to @MichaelHampton. Was finally able to confirm my local ISP was the issue and that the settings were working by launching a second AWS EC2 instance and testing the connection from there.

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