This post describes best practice to install and operate a FritzBox behind a Swisscom Internet-Box Router. The steps of course also apply for any other type of router delivered by the internet service provider. Such a setup might be preferred from persons who enjoy the high flexibility of FritzBox routers. Moreover, two approaches are presented how a landline phone number can be integrated, first by an analog interface and second over VoIP.
The basic setup consists of an Internet-Box 2 from Swisscom and a FritzBox 7490 from AVM. The Internet-Box 2 is used to establish the connection to the internet provider, in my case Swisscom. The FritzBox 7490 is connected over the ethernet port 1 to the ethernet port 1 of the Swisscom router. According to the recently tested BBCS equipment list , it would also be possible to connect the FritzBox directly to the service provider via the DSL/VDSL port. In my opinion, however, the option with two routers leads to two major advantages despite the increasing power consumption.
The Swisscom technicians are more willing to support me if there is a problem with the internet line towards my home because I only use original products from them. These products also include tools to debug and monitor the connection quality on my as well as on the provider’s side. Within my home network I should be able to solve any problem on my own.
By connecting the two routers in series I get a demilitarized zone (DMZ) for free. This additional firewall adds another security layer to my computers at home connected to the FritzBox. To improve the security level behind the FritzBox I only open the OpenVPN port on this router and may change the default port number.
The network of the Internet-Box 2 is configured as 192.168.1.0/24 and the FritzBox 172.16.1.0/24. On the Internet-Box a static IP is configured for the FritzBox’s MAC address. OpenVPN is used to access the home network behind the FritzBox over the internet. Therefore, on the Internet-Box, I forward incoming OpenVPN traffic (port 1194 UDP) to the FritzBox. For security reasons I only open this port on the FritzBox and forward it to the OpenVPN server within the home network. I never open any other port e.g. http, https, smtp, pop3 imap on the FritzBox to minimize security risks. All these services may be covered by dedicated servers connected directly to the Internet-Box.
To access the 192.168.1.0/24 network from 172.16.1.0/24 I added the following routing rule to the static IPv4 routing table of the FritzBox.
This configuration has the advantage that any device that is connected to the Internet-Box network can be access from the FritzBox network and even over a VPN connection trough the FritzBox network.
Integrating the Landline Phone
It might be a little outdated to use a landline phone but there are still good reasons to do so. Often the phone number is contained in the internet contract and comes to speak so for free. In companies, landline numbers are still very common and sometimes even required due to regulations e.g. contact information, impressum. There exist different methods to connect a telephone to the Swisscom router. Older phones may have a TT87 or TT89 connector and require a TT83 socket (also known as Reichle-Connector) or a RJ11 respectively RJ14 connector. These phones can either be connected directly to the analog phone connectors of the Internet-Box or with suitable adapter cables. For cordless phones the Internet-Box can be configured as DECT base station. This enables to connect of up to five DECT phones to the Internet-Box. Smartphones can be connected to the Swisscom router by installing the Swisscom Home App. Special settings are required to integrate a SIP phone. For security reasons, it is recommended to create local SIP credentials on the Swisscom router instead of using the external SIP data. The telephone function can be extended to the FritzBox by two approaches.
Connecting the FritzBox over the Analog Telephone Line to the Internet-Box
The first approach uses one analog telephone connector of the Internet-Box and some adapter cables as shown in the picture below. Thereby the adapter 058 from AVM is connected to the Internet-Box followed by the DSL/TEL splitting cable also provided by AVM. The Y-cable is then connected between the first mentioned adapter and the DSL port of the FritzBox.
On the FritzBox web interface the telephone is configured by adding a new telephone number under Telephony –> Telephone Numbers –> New Telephone Number.
Since we use an analog telephone line the
Landline number is selected as shown in the figure below.
In the next step the
analog line is selected.
Then the landline number provided by the service provider is entered without country code. The location information can be entered under Telephony –> Telephone Numbers –> Line Settings. The country and area code can be determined by the dropdown menu.
Finally, the settings for the analog line are stored.
The settings can be tested by making a call to an external number and from an external number.
Connecting the FritzBox with VoIP to the Internet-Box
For the second approach, the FritzBox 7490 is connected as SIP phone to the Internet-Box. For this purpose, the analog landline is deleted and the adapter cable for the analog telephone line between the Internet-Box 2 and the FritzBox 7490 is removed. In a first step, local IP phone credentials are created on the Swisscom router as shown in the figure below. The Internet-Box sets by default the username to something like
phoneuser<magic number>. These credentials may be used to connect a SIP client to the SIP server by this pattern
sip:username@address. That completes the settings on the Swisscom router.
On the FritzBox web interface a new telephone number is added like the steps described for the analog landline number. This time an internet telephone number is selected as outgoing caller ID. This leads to the setup to enter the configuration for the internet telephone as shown below. In the account information the option
Other provider is selected as telephony provider. The
Telephone Number for Registration is
222 and the
Internal Telephone Number in the FritzBox is the landline number provided by Swisscom. Under
Account Information the Internet-Box credentials are entered. All these settings can be obtained from the Internet-Box 2 web interface by clicking the edit button of the local IP phone credential or by viewing the configuration data at the bottom of the same page. Finally
Use telephone number for registration is enabled under
Additional Settings for the Connection.
Next, a summary is generated where the configuration check is enabled.
By the end of this test, the telephony check should be successful as shown in the figure below.
The final configuration looks like this.
On the Swisscom router web interface under the IP phone credentials the status of the FritzBox user should be
Phone registered. One my test the phone by clicking the
Ring test and if that was successful by calling again an external number.
The installation and configuration of the two routers is relatively easy. The numbers of cables can be reduced by integrating the phone using VoIP. The subsequent figure shows the final installation next to the office desk. With proper cable management the installation does not look too bad.
A long-time test showed that the setup works reliable. The telephony function of the FritzBox works well even with the FritzBox Phone App over VPN. Moreover, it is possible to make service provider independent internal phone calls. It is for example possible to call a DECT phone from a VoIP phone and vice versa. This is especially helpful for small businesses who have multiple phones for different people at different places. Furthermore, Softphones e.g. PhonerLite can be connected either to the Internet-Box or the FritzBox.