(...replying to myself...)

Ignore my comments about the dst-nat rules.  I misread your posts and thought 
you had said that you successfully managed to connect directly to your SIP 
trunk provider *from your Android phone* and *from within your network*.  Now I 
see that you are using those dst-nat rules to make your FreePBX server 
accessible to remote extensions from the outside, and that your Android phone 
is set up as an extension, *not* that you were registering to your SIP provider 
from your handheld.

My only comment on that would be that requiring a VPN connection rather than 
doing the port-forwarding might be safer and better protect you from toll 
fraud. :)  But at least I see what you are doing with those now.

I haven't tested this theory, but the reason why I suggest you try temporarily 
disabling that drop rule for forwarded traffic with an invalid connection state 
is that everything I've read so far seems to suggest that anything is 
considered an "invalid" connection if it A) doesn't already have an entry in 
connection tracking, and B) it is not a "new" connection, which basically means 
TCP SYN.  Unlike TCP, my understanding is that UDP really doesn't have easily 
definable connection "states", so I'm not actually sure that the 
"connection-state" firewall matcher is compatible with anything other than TCP 
(or that it makes sense to apply it to anything other than TCP).  Again, I have 
not tested or verified this.  But if this is the case, then it's possible that 
rather than ignoring UDP traffic, the filter rule might be blindly tossing 
anything UDP that is being forwarded.  (You did say that you see the packets 
being received from the FreePBX box, but that they were being dropped b
 efore being forwarded...)

If disabling that rule fixes your problem, and you want to keep a rule like 
that in place, you might try making it more specific by adding additional 
matchers, such as "protocol=tcp" and perhaps even "in-interface=<WAN>".

--
Nathan Anderson
First Step Internet, LLC
nath...@fsr.com

On Thursday, January 29, 2015 5:30 PM, Nathan Anderson wrote:

> Are you doing SIP over TCP or UDP from FreePBX?  (Guessing UDP.)
> 
> Are you doing SIP over TCP or UDP from your Android phone that works? 
> (Guessing TCP.) 
> 
> Can you try either disabling the last rule in your firewall filters list
> (action=drop chain=forward connection-state=invalid), and/or also setting
> protocol=tcp on it, and then try to originate SIP traffic from your
> FreePBX server again?   
> 
> They probably aren't harming anything, but unless your SIP trunk provider
> isn't requiring you to send SIP REGISTER to them and instead uses
> IP-based authentication, you don't need all of those dst-nat rules
> pointed at your FreePBX box.  The kernel's connection tracking should be
> able to figure all of that out.    
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