SIP ALG Fails without any firewall

[Michael Moore]

The primary interface of our 3CX is connected directly to our comcast internet connection with a static IP. We're not using any firewall on that interface. Everything on the firewall check succeeds except:
testing 3CX SIP Server... failed (How to resolve?)

• stopping service... done
• detecting SIP ALG... failed (How to resolve?)
• testing port 5060... done
• starting service... done
  

Any ideas as to how to resolve? We don't have any devices in between the 3CX and the ISP's router.​

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[lneblett]

You may need to inform Comcast that the modem needs to have its SIP ALG disabled. Many cable modems have such ALGs embedded as some customers do not have their own router and the modem acts as one to include the firewall.

 

[Michael Moore]

Thanks. That's the most obvious answer so you're probably right. I'll open a ticket with Comcast and see if they can check the cable modem's config.