[Freeswitch-users] NAT issues and "best practices"

Sean Devoy sdevoy at bizfocused.com
Fri Jun 1 05:32:41 MSD 2012

Thanks for the response.


At this point I can say I have  2 working and 1 not working configuration.
Also, thanks for the SIP ALG tip (3 hours too late!)  I turned it on and
things went to crap.


So my WOKING configa are:

<FS w/ local IP> to <FIOS 25MB router> to <Motorla Cable Modem> to <Cisco
RVS4000> to <CISCO SPA-504G phones>

<FS w/ local IP> to <FIOS 25MB router> to <Motorla Cable Modem> to <Linksys
home router ???? > to <CISCO SPA-504G phones>

Calls, MWI, SCA, etc across those 2 configs works PERFECTLY.

I left out <fs> on local lan to <Cisco 504g> is wonderful too.


Unfortunately, the customer setup is:

<FS w/ local IP> to <FIOS 25MB router> to <COMCAST Business Cable Modem> to
<Cisco E1200> to <CISCO SPA-504G phones>

Results are all over the place.  I don't think they can support 2 inbound
calls at the same time.  MWI is spotty, SCA is not working.  Turning on SIP
ALG on Cisco E1200 led to a small riot and has been banished from the
kingdom for every.


I think tomorrow we are getting them a Cisco RVS4000.





From: Ashley Breeden [mailto:ash at url.net.au] 
Sent: Thursday, May 31, 2012 7:52 PM
To: FreeSWITCH Users Help
Subject: Re: [Freeswitch-users] NAT issues and "best practices"


Hi Sean,


Yes SIP and NAT do not play well together.  Most of our customers all use
some form of NAT to access our FreeSWITCH servers, although not double NAT.
I have found that pretty much most of the current mainstream routers and
phones work as long as you have the latest software.  One of the biggest
things I find is that if you have more than one SIP device registered behind
a NAT with SIP ALG you will get very mixed results.


It will also depend on how many devices you have behind the NAT, some
routers seem to have issue processing NAT for more than 10 devices all
originating on port 5060.


Here is a few things I will often do to get a customer to connect via a NAT


- Turn off SIP ALG on the router

- Look for a setting on your VoIP device called Rport, set this to enabled.

- Try putting each phones local SIP port on its own unique port, e.g.
extension 1001 = port 5001, 1002 = port 5002

- Try TCP as the transport protocol


Also have a look here I have been able to get some useful information from
this article - http://wiki.freeswitch.org/wiki/ALG, especially the DG834's
with DOS protection.


Personally I use the following routers with no issues:


- Billion 7401VGP

- Billion 7800NL

- Billion 7404

- Cisco 857/877

- MicroTik seemed to be quite reasonable as well


For Phones I have running:


- Yealink T22,T26,T28,T32,T38

- Snom 360

- Siemens Gigaset



Hope this helps.







On 01/06/2012, at 4:10 AM, Sean Devoy wrote:

HI All,


I have a customer location that has just been a nightmare to implement.  I
am just learning that they "may" have multiple NAT routers in sequence at
their location.  I think I fully understand what NAT is trying to
accomplish. There seem to be different levels and approaches. 


The most basic NAT setup (to me)  is a HOME LAN with multiple PCs where NAT
allows multiple devices to share a single routable IP address on the WAN
side from multiple local devices the LAN side.  Note I said OUTBOUND
initiated connections.  Even FTP can have trouble with this level.  Almost
all inbound traffic is blocked for security.


Clearly for FS we need the switch to be able to punch through from the WAN
to specific local IPs on the LAN to reach specific phones.  This is INBOUND
NAT and brings up many security issues for people.  Even on devices where
you get this "working" you may only be able to support one line per phone or
a single inbound connection at a time.


I understand NAT has PMP and UPnP protocols and FS "supports" both.  What I
can't find is where someone says "Here is a great setup that works with
cheap, available "commodity" hardware from Cisco/Linksys that supports all
the NAT you need for FS."  I don't care if it is PMP or UPnP and I might not
even care why you pick one over the other, although it is probably a "good


Can someone just stand up say "FS works GREAT with the XYZ router in ABC
mode from MY COMPANY using NAT to Cisco phones"?


I have seen some articles about Freeware/Shareware firmware in this devices,
but as a novice I want to limit the unknowns until I get more up to speed.


My specific issue now is that I cannot get SCA to work at the NAT location.
I issued:

sofia_contact 220 at mydomain.com

sofia/external/sip:200@<ip address>:44234,sofia/external/sip:200@<same


Only one phone rings on inbound and the line indicator light does not change
when either is picked up.  Same configuration is working on our LAN with the


I am absolutely ready to by a router to fix these issues, I don't want to
lose this customer.


Thanks for your thoughts,


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