[Freeswitch-users] Control SDP IP used between internal and external bridge

SIP Tech siptech at onereach.com
Wed Apr 12 02:05:17 MSD 2017

Great work on the FS project guys!  I have a specific use case on a
seasoned freeswitch machine that seems to be giving me problems based on
SDP, working NAT configs, and freeswitch.  First off, NAT works and my
machines are resolvable by internal IP within the network and publicly via
static public IP.  My issue is not a functional NAT issue but how
freeswitch assigns a private or public IP in SDP.  I would like to control
IP used in SDP at bridge, so that I can use private IP or public IP on
demand where I want to instead of letting freeswitch insert it based on
config settings.

My scenario is all controlled via configs within freeswitch.  All machines
have private and public IPs but specific traffic must pass over private IP
and in other places calls must bridge to another FS machine via external
profile and public IP.

Internal Profile= UPD 5080

External Profile= UDP 5060

1. A private call comes into freeswitch A over an MPLS to my internal SIP
profile on UDP 5080.

2. The call then routes from freeswitch A via bridge to freeswitch B via
public IPs on the external profiles using UDP 5060.  Freeswitch B is only
accessible via its public IP address.

3. Freeswitch B routes calls to a 3rd party IVR that gives callers the
option to transfer back to Freeswitch A.  When the caller selects to be
transferred within the IVR freeswitch B makes a bridge back to freeswitch A
using public IPs.
4. Freeswitch A receives the incoming call from freeswitch B public IP to
public IP.

5. Freeswitch A uses another dialplan to route the call back out over the
MPLS using private IP to private IP.

I am running into SDP IP issues and how freeswitch is handing SDP based on
where the call came from and where it needs to go to.  I have spent some
time playing with configs in vars and the profiles around rtp ports and
ext-rtp nat, autonat, etc. I have SDP working how I need it to up to the
last step (4 and 5 above) but I cannot get freeswitch to send its internal
IP out in that last SDP session on bridge back over the MPLS.  The MPLS
only talks private ip to private ip and FSA is sending its public IP in

This is where I am looking for an explicit way to control which SDP IP
(local machine private or public) is sent out on bridge.  Is this
possible?  If not, Is there a better way or alternative way to
approach this scenario in freeswitch?

Thanks guys
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