Two network interfaces

I have a problem with phones logging into my freepbx install remotely. The problem started when my ISP and SIP trunk provider split the services in two network drops. I had to add a second interface to my PC that is running the switch.

I log into the SIP trunks via one interface with a public IP. This public IP is not usable other than to access the sip trunks. All other traffic on the switch goes out over an interface with a internal ip address.

Only phones on the lan can make phone calls. Phones that are logged in from the internet don’t have any audio and disconnect after a few seconds… classic NAT problem.

Under sip settings I have to set the External Address to the IP that is used to access the trunks or they can’t register.

Everything was great when I had only one address to access both SIP trunks and the internet.

This is an incredibly frustrating problem that I have been messing with for weeks.

Looks like you are creating a split-route condition where traffic comes in one interface and leaves another. the remote end sees connections coming from an ip address it has not attempted to talk to and drops packets.

if the interface is only allowed to communicate with your sip provider and is a default gateway for the phone server, it cannot be used for external phone registrations. In this case you could VPN your pones to the local lan and they would act like your local phones.

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i think you need to add the appropriate route commands to ensure that traffic is routed out over the proper nic.


You will need to set up a static route towards your ITSP. It should be a on a special file in the Linux OS. The location is in the /etc/sysconfig/network-scripts

The name of the file should be route-eth1 for example if your ITSP is connected to eth1.
The static route in this file should be like this:

[destination network/cidr] via [ip address of your ITSP router] dev [device name]

for example: via dev eth0

Upon completing this restart the networking service:

service network restart

To verify that the route is in place, type this command:

ip route list


netstat -rn

Thank you,

Daniel Friedman
Trixton LTD.

Tel: 972.72.2557000 Ext.1
Mobile: 972.50.6655579

Email: [email protected]

Hi, I have exactly the same problem, did you get a solution?

I have this kind of problem too, but everything is working fine except when i want to blind transfer
or use always forward to another phone, then after 30 seconds my call drops