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Notes about routers as they apply to FreeSWITCH™ applications.

Apple AirPort Extreme

Using an Apple AirPort Extreme in NAT-PMP mode, it is pretty much Plug-n-Play. Simply enable NAT-PMP, Port Mapping is not required. FreeSWITCH detects NAT-PMP and enables the required ports. I have tested this using a new AirPort Extreme, Firmware Version 7.4.2. Static IP Address assigned to the WAN, NAT-PMP enabled, FreeSWITCH server assigned a static RFC-1918 address on the LAN. Pointed DNS record for the server to the static address of the router. Installed iSip from the Apple iTunes Store on my iPhone 3GS, registered the client to the DNS of the FreeSWITCH, added user/pass information and was able to place a call through the 3G network thanks to 3G Unrestrictor (jailbroken phone) which is available through the Cydia store. RTP sets up correctly, two-way audio works and this was using stock configs from installing the sample configs.

Let me know if you need more info!

ActionTect MI424WR - Verizon FIOS

I am running Cisco SPA504g and Polycom 335 phones through this NAT Router. I was succesful with 2 different configurations. Using any SINGLE phone does not appear to need any router changes, just the NAT setup on the phones. For multiple phones we first got them working with NDLB-connectile-dysfunction and NDLB-force-rport in each of the user profiles AND enabling SIP ALG on the router.

I was later able to turn OFF SIP ALG (as many people reccomend) with changes in the phones configurations. For each LINE (i.e. SIP Registration) used on each phone I had to configure the LOCAL SIP Port to a unqiue port. It appears that this router has a 1-to-1 mapping of external ports to internal devices with SIP ALG disabled. I am refering to the sip port on the phone end not the FS Server SIP Port.


The DOCSIS combination cable modem and router supplied by Comcast employs a SIP ALG that causes numerous problems with telephony. Users report phones not registering or registering intermittently, calls dropping, NAT traversal problems, and others. Here's an anecdotal exchange on the FreeSWITCH users mailing list from early January, 2016

Comcast Knowledgebase

On Jan 9, 2016, at 11:24 PM, Sean Devoy <> wrote:

> The extension did not have

> <variable name="sip-force-contact" value="NDLB-connectile-dysfunction"/>

> And all the working extensions do have it. I added it.

> I don’t know what else happens when that is set, but I know it makes my extension re-register every 30 seconds (which seems excessive to me). I think that is probably just masking the underlying problem where the Comcast router is dropping the NAT connection after some time period. I am thrilled to have it working, but there must be a cleaner fix. Is there at least a way to extend that 30 second time to 60, 90, 120?

Daniel Corbe <> wrote:
This is slightly off-topic; however, it really is your Comcast-supplied CPE causing this particular issue. You’re better off buying an inexpensive cable modem that only runs in bridge mode and using a router that you have more direct configuration control over. The person that maintained this before you obviously took note of how stupidly aggressive the default timers are on their CPE.

Larry Morley <> wrote:

We had customers experience the same problem - and others apparently stemming from the same root cause - particularly with this ISP. And, it turned out they had experienced the same problems with their phone service when they were receiving it from the company before us.

The cause of that problem, along with others such as users receiving calls from their own extensions several times an hour, 24x7, were ultimately determined to be the result of Comcast having an incompatible SIP ALG enabled on the CPE: a SIP ALG that's properly implemented and properly working shouldn't cause any issues. Also, the users that experienced the worst variants of these problems had a SIP ALG, and apparently other ALGs for other protocols, enabled on their own routers.

Calling Comcast technical support and requesting that they change the "cable router" settings, then power cycling the CPE and the local routers as necessary, invariably solved the problem(s) we'd been experiencing.

Note that in the course of fixing these issues, we discovered that, according to the current DOCSIS specifications, by design, end users aren't supposed to be able to modify much with respect to DOCSIS "cable modem" settings. That's why we decided to go the ISP tech support route first.

We haven't seen a recurrence of any of the problems noted initially since we made the changes noted, well over six months ago.

Hopefully this is of use to someone.

MiFi 2200 - Verizon Version

Running FreeSWITCH on a netbook using this 3G router as a gateway. Plug and Play. No adjustments needed. The reason I'm using FW instead of something more straightforward such as Twinkle is that I wanted to use a WIFI phone that did not traverse NAT well.

See notes in Cisco SPA 3xx/5xx and Polycom Generic sections above on phone settings.