[asterisk-bugs] [Asterisk 0016771]: T.38 with devices behind NAT does not work

[Asterisk Bug Tracker]

A NOTE has been added to this issue. 
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https://issues.asterisk.org/view.php?id=16771 
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Reported By:                ipich
Assigned To:                
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Project:                    Asterisk
Issue ID:                   16771
Category:                   Channels/chan_sip/T.38
Reproducibility:            always
Severity:                   minor
Priority:                   normal
Status:                     feedback
Asterisk Version:           1.6.2.2 
JIRA:                        
Regression:                 No 
Reviewboard Link:            
SVN Branch (only for SVN checkouts, not tarball releases): 1.6.2 
SVN Revision (number only!):  
Request Review:              
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Date Submitted:             2010-02-04 07:42 CST
Last Modified:              2010-02-05 02:52 CST
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Summary:                    T.38 with devices behind NAT does not work
Description: 
I've found trouble described in
https://issues.asterisk.org/view.php?id=10417
There is patch for 1.4, but I have 1.6.2, so it does not work

Scenario is :
Host1 192.168.x.x (NAT IP 100.100.100.100) sends fax host2 200.200.200.200
but after re-invite t.38 session asterisk transmits udptl packets to
internal IP 192.168.x.x
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 (0117770) ipich (reporter) - 2010-02-05 02:52
 https://issues.asterisk.org/view.php?id=16771#c117770 
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"The patch you are referencing added a configuration option which caused
Asterisk to send UDPTL to the IP address of the RTP, and to the port
negotiated for UDPTL. If the port was forwarded then it could work."

It's correct. 
So I've made new tests with another device - Addpac. This device
advertises the same udp port for UDPTL session as the RTP session,
therefore socket is alive and it must faxing but asterisk still transmits
to internal IP rtp port, not nat IP and rtp port. Check my
t38_192.168_for_mantis.log trace

"we get no packets from the other side so we can't use the source IP
address/port"

Sorry for my knowledge base, what you mean 'we get no packets from the
other side'? What type of packets? I've made test for available host from
Asterisk - this is 172.31.255.250, this is not NAT ip and Asterisk pings
that

I've seen that first UDPTL packet from Addpac follows after UDPTL packets
from Asterisk and fax passes. Check my t38_172.31_for_mantis.log trace

So my question is why asterisk transmits to internal IP, I do not see any
attemps (even fail attemps) to transmit to NAT IP. 

Issue History 
Date Modified    Username       Field                    Change               
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2010-02-05 02:52 ipich          Note Added: 0117770                          
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