SIP ALG Problems

Using VOIP.MS service I had no problems for months with a single device. Recently I added a second device (an Obi202) and set it up properly (e.g. using its own sub-account at

Started having problems with one device (or the other) failing to register, and it seemed periodic.

I checked the Peplink / Status / Active Sessions and both devices were showing up as expected.

Per advice of VOIP.MS I moved the second device from 5060 to 5080 and it seems more stable now. I did not turn off the Peplink SIP ALG, but did add port 5080 under Peplink/Network/Misc/Service Passthrough/SIP/Define Custom signal port.

My question: do I really need to have the two devices connecting on different ports? One would expect that the Peplink built in ALG should handle this, no?

Edit to add:

At one point when device 1 wasn’t registered, I looked at my account status and it showed that device 2 wasn’t registered, which was backwards from reality. This makes me wonder if the Peplink may have been routing packets meant for device 1 to device 2 or vice-versa.

Edit 2 to add:

Both devices are on the same VLAN, in case that’s relevant.

Please find the forum thread below. This is related to the ISP. Look like you are having the same problem.

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It sounds like f you have multiple SIP devices on port 5060, then the Peplink will do NAT/port translation, and it may choose port 1025 (which many ISPs block) resulting in problems. I’m not clear if this is an ISP problem or a Peplink issue that could be fixed?

In any case, by hard-coding one of my SIP devices to use port 5080 instead of 5060, I’ve had zero problems for over a week.

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Came up against similar VoIP issues with a Pepwave Surf SOHO MK3

My Environment
1x(New GB 8P SW) 1x(i7PC) 2x(Grandstream GX2140) + PEP +Circuit=CableInet


  1. Obvious issue had been SIP traffic dropping after 10 minutes of being in use.
  2. Desktop VoIP Phones would get bounced off the network as if they were locally blacklisted by the PEP router and could not ping from same network.

Steps I took that did not resolve my issue:

  1. Change DHCP segment from default x.x.50.x to x.x.0.x
  2. Change Advanced>Service Pass-through> Standard to Compatibility mode.
  3. Upgraded Firmware to 7.0.3 build 1260
  4. Factory Rest PEP

Steps I took that did resolve issue:

  1. Dashboard > WAN > Details > Enabled “Independant from Backup WANs”

Pepwave Surf SOHO MK3 device is routing traffic improperly and requires intervention to tell router to not use other routes.