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howtos:misc:proxying_smtp [2015/11/27 23:07 (UTC)]
louigi600 [Scenario 3]
howtos:misc:proxying_smtp [2016/06/20 07:28 (UTC)] (current)
alienbob proxying_smtp renamed to howtos:misc:proxying_smtp (Ended up in the wrong namespace)
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 Here are some scenarios with examples on how you could go about working around the problem. Here are some scenarios with examples on how you could go about working around the problem.
  
-Throughout the scenarios we will be referring so 3 machines:+Throughout the scenarios we will be referring to 3 machines:
  
-  * Machine A with IP address 192.168.0.2 (cannot send meils directly via internet and cannot use Local Mail Relay)+  * Machine A with IP address 192.168.0.2 (cannot send mails directly via internet and cannot relay on Local Mail Relay)
   * Machine B with IP address 192.168.1.2    * Machine B with IP address 192.168.1.2 
   * Local Mail Relay (LMR) with IP address 192.168.2.2   * Local Mail Relay (LMR) with IP address 192.168.2.2
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 ===== Scenario 1 ===== ===== Scenario 1 =====
-Machine A cannot send mails directly (has no local MTA and cannot access directly any other RELAY) +  * Machine A cannot relay on any local or internet MTA 
-but Machine A has access to machine and Machine B can access LMR's port 25 and is allowed to use LMR for relaying mails.+  Machine A can reach Machine on some unused port (1234 in the example below) 
 +  * Machine B can relay thought LMR 
 +  * Machine B can reach LMR's port 25
  
-We can use nc to proxy mail from A to LMR+We can use nc on Machine B to proxy mail from A to LMR. In this example it will appear to LMR as if it was Machine B that is sending the email.
  
 On machine B On machine B
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 ===== Scenario 2 ===== ===== Scenario 2 =====
-Let'suppose that Machine A can reach the LMR but only on port 22 +  * Machine A cannot reach LMR'port 25 
-can we use a ssh tunnel between A and LMR to do the job for us ?+  * Machine A is allowed to relay thought LMR but firewall is preventing it from reaching port 25 on LMR 
 +  * Machine A can reach the LMR but only on port 22. 
 + 
 +We use a ssh tunnel between A and LMR to do the job for us. In this example we are bypassing firewall by using ssh to forward traffic trough a encrypted tunnel. For this to work properly the ssh client that is going to be forwarding needs to be executed by an administrative account.
  
 <note important>This time we will be working exclusively on machine A</note> <note important>This time we will be working exclusively on machine A</note>
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   DATA   DATA
   354 End data with <CR><LF>.<CR><LF>   354 End data with <CR><LF>.<CR><LF>
-  FROM:drao@invallee.it +  FROM:me@localnet.com 
-  TO:drao@invallee.it+  TO:dude@localnet.com
   SUBJECT:test using ssh tunnel   SUBJECT:test using ssh tunnel
   if you get this sending email trough ssh tunnel worked   if you get this sending email trough ssh tunnel worked
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- +===== Scenario 3 =====
-This method may or may not work depending on whether MTA on LMR is configured to allow Machine A to relay trought it. This leads to yet another scenario (see Scenario 3) or an alternative method provided the following conditions are met:+
   * Machine B can relay emails trough LMR    * Machine B can relay emails trough LMR 
 +  * Machine B cannot reach LMR's port 25
 +  * Machine B can access LMR via ssh
   * Machine A has access to Machine B on whatever port we choose to let ssh listen on for forwarding (1024 in the exaple).    * Machine A has access to Machine B on whatever port we choose to let ssh listen on for forwarding (1024 in the exaple). 
  
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 We can then start the ssh socks proxy on Machine B listening on a port Machine A can access: We can then start the ssh socks proxy on Machine B listening on a port Machine A can access:
  
-On machine B+On machine B with a privileged user
   ssh -2 -D 192.168.1.2:1024 -N  192.168.2.2 &   ssh -2 -D 192.168.1.2:1024 -N  192.168.2.2 &
  
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   DATA   DATA
   354 End data with <CR><LF>.<CR><LF>   354 End data with <CR><LF>.<CR><LF>
-  FROM:drao@invallee.it +  FROM:me@localnet.com 
-  TO:drao@invallee.it+  TO:dude@localnet.com
   SUBJECT:test using ssh tunnel   SUBJECT:test using ssh tunnel
   if you get this sending email trough ssh tunnel worked   if you get this sending email trough ssh tunnel worked
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-===== Scenario ===== +===== Scenario ===== 
-Mostly like Scenario 2 but Machine A is not allowed to relay on LMR dew to MTA configuration.+  * Machine A cannot reach LMR's port 25 
 +  * Machine A is not allowed to relay thought LMR  
 +  * Machine A cannot proxy on any other machine that is allowed to relay trough LMR 
 +  * Machine A can reach the LMR but only on port 22. 
 We can still get the whole command to run on the LMR via ssh: We can still get the whole command to run on the LMR via ssh:
 +
 +<note important>This time we will be working exclusively on machine A</note> 
  
   cat << EOF > send_this_mail   cat << EOF > send_this_mail
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 ====== NOTES ====== ====== NOTES ======
-The command we used above is probably a good example of bad unixcraft, let me give a brief explanation on how it works.+The command we used in Scenario 1 is probably a good example of bad unixcraft, let me give a brief explanation on how it works.
 Let's momentarely get rid of the odd use of the fifo by just using this: Let's momentarely get rid of the odd use of the fifo by just using this:
  
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 so now the whole command line looks like this: so now the whole command line looks like this:
   cat /tmp/f | nc -l -p 1234 -s 192.168.1.2 | nc 192.168.2.2 25 >> /tmp/f   cat /tmp/f | nc -l -p 1234 -s 192.168.1.2 | nc 192.168.2.2 25 >> /tmp/f
-it is possible to do the same thing without having to use cat it is a little neater but still bad unixcraft+it is possible to do the same thing without having to use catit is a little neater but still bad unixcraft
   nc -l  -p 1234 -s 192.168.1.2 < /tmp/f |nc 192.168.2.2 25 >> /tmp/f   nc -l  -p 1234 -s 192.168.1.2 < /tmp/f |nc 192.168.2.2 25 >> /tmp/f
  

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