Balance 20 kills VOIP fax

I have been running our fax through a Cisco SPA122 since we switched to Vonage Business. Everything was working fine before the Balance 20 was installed. I am able to receive at least some faxes, but I am unable to send successfully. I can hear the handshake, but get a “fax failure” message about 30-40 seconds afterward.

The SPA122 has two phone lines, the other of which is used for voice and is still working.

What config changes does anyone think I need to make to get my faxes working again?



Try compatibility mode under: Network> Misc. Settings> Service Passthrough Support which turns off SIP ALG. Does that solve the issue?

I gave that change a try and let it run for a day to see if it helped. I was able to get one test fax through but so far that is it. I am still being told that faxes can’t be sent.

Hi Okkman - Do you have multiple WAN’s connected to the Balance 20? Seeing as how some faxes get though but some do not, it may be a load balancing issue and you will have to create an outbound policy for the Fax Machine to use the same link all the time if available. Thanks, Mike

Yes I do. My Outbound policies are currently the defaults (HTTPS Persistence on top, default under it). Can you suggest the correct policy definitions for this situation? I’m not quite that net literate unfortunately.

Under Network> Outbound Policy, add the following rule:

Source = IP address of the FAX machine
Destination = Any
Protocol = Any
Algorithm = Priority (preferred WAN on top, failover WAN below that)

Just for the benefit of anyone else having this problem, I implemented the outbound policy and made the “compatibility mode” change mentioned above and it seems to have taken care of the issue. Thanks Ron!

And today it’s not working, so I spoke too soon…


Same behavior (fax in ok but not fax out)? Please open ticket for us to investigate.

We were having this problem with some IP Phones a while back: A reboot or Peplink settings change would allow our devices to receive calls, but only for a day. The following day, we could originate calls, but not terminate them. We ultimately learned that the only solution was to TOTALLY disable the SIP ALG from a hidden settings page. That resolved the problem permanently for us.


The SIP passthrough at Network > Service Passthrough and Support.cgi page is same.

Anyway thanks for your sharing :up:

Do I have to open a ticket to get to that page?

After logging into the Balance, type in this URL to get to the support.cgi page:

http://<Your device’s IP>/cgi-bin/MANGA/support.cgi

I can see on that page that SIP ALG is already disabled.


Please open ticket if you still having intermittent fax issue.

Hello TK,

My ticket number is 749260 and although the advanced team is working on it, we still have the problem.

Hi okkman,

Noted and thanks for the reply. We shall feedback on the finding soon.