A very unusual PBX Scenario?


I am working on a PBX topology that’s probably very uncommon.

We are a service provider, who are testing SIP trunks with Asterisk. So for now, we are using an SBC to send a trunk (public/client-realm) to the Asterisk PBX and connect through the SBC to the MGC on its private-realm.


  1. SBC Trunk/Asterisk-Server is on : 172.1.10.x/24
  2. SIP phones: 172.1.11.x/24
  3. Public IP: 213.x.x.x/30

All interfaces are routed through a cisco router.

Question is, in such a scenario, would it be possible to:

  1. Configure SIP clients/users from the internet?
  2. TO connect SIP clients from the internet, would configuring port-forwarding on the cisco router alone (from public-ip 213.x.x.x/30:5060 -> 172.1.10.x/24:5060) be enough to register with the asterisk Server?

I’d like to hear your thoughts on whether this is doable or/and if anyone has experimented with something similar.